Biology Notes, Module 2, Blueprint of Life, by F.A ... · Biology Notes, Module 2, Blueprint of Life, by F.A 4 | P a g e because of the rate in which they reproduce. Economically

Biology Notes, Module 2, Blueprint of Life, by F.A

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Blueprint of Life


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1. Evidence of evolution suggests that the mechanisms of inheritance, accompanied by selection, allow change over many generations

Outline the impact on the evolution of plants and animals of:

– changes in physical conditions in the environment – changes in chemical conditions in the environment – competition for resources

While organisms are so different they also have many common characteristics:

- they all have a similar chemistry – all living things are mainly made of carbon, oxygen, hydrogen and nitrogen which are always connected to form proteins, fats, carbohydrates and nucleic acids

- they are all filled with water - they all have the same fundamental cellular structure – they are all made of cells and the cell membranes all have a

similar chemical structure - they all use DNA and RNA as the same basic type of genetic material - they all (except chemosynthetic bacteria) use enzymes made of protein to control their chemical reactions - they all use the same type of chemical reaction, respiration to make energy available in cells

The “Evolutionary Theory” states that all organisms have a common origin in some initial form of life, which, over billions of years of change in many different directions, has given rise to the vast variety of organisms – present and past. According to this all living things are similar because their basic chemistry has been inherited from this very first organism

Evolution and the changing chemical environment

When life first evolved, it developed in an anoxic environment As these primitive organisms metabolised simple organic molecules, carbon dioxide was released Over millions of years carbon dioxide accumulated and at some stage organisms capable of using this carbon dioxide in photosynthesis evolved and multiplied They produced oxygen as a product from their metabolism which created an environment animals could exploit Animals obtained energy from aerobic respiration

As life altered the chemistry of the atmosphere, so too the chemical changes impacted on evolution

The evolution of organisms because of changes in the chemical environment is not just in the past but affects us now

Example: malaria spreading mosquitoes were thought to be easily eradicated using DDT but as some mosquitoes were already immune to DDT they survived and produced a resistant mosquito population

Example: antibiotics used to treat bacteria-caused disease have become less effective as resistant forms of bacteria have evolved. Drug companies are constantly researching new antibiotics that might be effective against resistant bacteria strains

Evolution and the changing physical environment

The physical environment has changed frequently with rises and falls in the sea levels; even parts of Australia have been covered by oceans or dry land at different times. Such drastic changes in the environment influence evolution

Fossil evidence indicates that many mass extinctions have resulted from changes in the Earth’s physical environment

Example: at the time the continents came together to form Pangea, about 90% of marine mammals became extinct

Example: the best-known mass extinction is that of the dinosaurs for which there are many theories but most of them are due to a climate change. But the environmental change favoured those mammals that evolved best

Example: As Australia drifted north, the continent became drier and the soils became poorer. After once being dominated by lush vegetation, like beech forests sclerophyllous plants such as eucalypts became the more dominant vegetation as they were better adapted to these environmental changes and these plants rapidly became the dominant flora of Australia

Environmental change can favour one group of organisms over another


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Evolution and competition

During the Cretaceous period, the success of mammals was limited because the niches to which they eventually evolved were occupied by species of dinosaur. When the dinosaurs died out mammals had few competitors and diversified to occupy the many available niches in the ecosystem

Long-term competition usually results in the elimination of one of the competing species or the evolution of the competing species to occupy different niches

PRACTICAL Plan, choose equipment or resources and perform a first-hand investigation to model natural selection Aim: To perform a first-hand investigation to model natural selection Background: Consider a hypothetical population of lizards and make the following assumptions for this activity

Three variations of lizards exist: red, orange and yellow

The original population of 30 lizards is composed of 10 red, 10 orange and 10 yellow lizards

Each year the lizards mate at random and each pair produces one offspring according to the table:

Each year after the lizards breed a predatory bird kills one third of them (15 lizards) in the ratio of 3 red : 2 orange : 1 yellow

At the end of the year there remains a population of 30 lizards to begin random breeding once again

No other factors cause changes in the population Method:

1. Take out 10 cards of each colour – represents original population. The remaining cards are used for offspring 2. Shuffle the 30 cards thoroughly and deal out 15 pairs – this represents the random mating of parent lizards 3. Examine the pairs created and use the table above to determine the offspring 4. For those with a ratio create a square spinning top divided into four triangles. For the half ratios 1 and 2 can be one

alternative while 3 and 4 is the other 5. Once the offspring has been determined add the appropriate cards to the population to represent the offspring 6. The new population should have 45 lizards. The predatory bird will eat 15. To determine which individuals are to be

selected use a hexagonal spinning top, marked according to the ratio mentioned above. Spin and remove 15 lizards 7. Repeat steps 2-6 four more times indicating five full generations have gone by 8. Tabulate the results as you go indicating population before and after predation and discuss your results

Conclusion: The resulting population will contain mainly yellow and some orange lizards, but no red this is due to the predatory habits of the bird. It can be assumed this is a result of the environment with yellow and orange lizards being better adapted to hide from these birds. This is a good model of natural selection as it mimics the way adaptation (colour) can be an advantageous for survival and hence the less advantageous trait is slowly bred out of the population. However, this model is basic as it does not take other environmental factors into account and the population being used is very small. Similar results in real life would take millions of years.

PRACTICAL Analyse information from secondary sources to prepare a case study to show how environmental change can lead to changes in a species Case study – Myxomatosis and Calicivirus

European rabbits were introduced to Australia in 1859 and have been an ecological and economical pest. Ecologically they threaten the survival and existence of native plants and animals. The rabbits compete with the native animals for the same food and because they can reproduce so quickly they drive the native fauna away. Similarly because they are in such large numbers they consume the vegetation at such a rate that the native plants also struggle to survive. Predators are never much of a problem

Parents Offspring

Red x red Red

Yellow x yellow Yellow

Red x yellow Orange

Orange x orange ¼ red : ½ orange : ¼ yellow

Red x orange ½ red : ½ orange

Yellow x orange ½ yellow : ½ orange


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because of the rate in which they reproduce. Economically they are seen as a pest to farmers especially those who farm vegetables as the rabbits eat their produce. And for other farmers they eat the pasture that their livestock need. To control the numbers of rabbits a virus called myxomatosis was introduced in 1950. This virus is carried by fleas or mosquitos and causes the myxomatosis disease in the rabbits. While the virus was initially extremely successful as the years went on the rabbits developed a resistance and the virus itself had decreased in virulence. In response to this a second method to control rabbit numbers was introduced – the calicivirus, which only affected rabbits. The virus is spread by direct contact between rabbits and causes death within 24 hours of infection. The virus was accidentally released in 1995 from an island in South Australia where it was being tested but proved to be extremely successful and it was officially released in 1996. While the effects are being monitored throughout Australia it can be assumed that just as the myxomatosis virus decreased in virulence and the rabbits formed a resistance to it the calicivirus could be the same. Scientists must therefore continue their research within this field. Describe, using specific examples, how the theory of evolution is supported by the following areas of study:

– paleontology, including fossils that have been considered as transitional forms – biogeography – comparative embryology – comparative anatomy – biochemistry

Biological evolution states that all organisms have developed from pre-existing organisms

The theory of evolution can be tested by examining fossils and comparing organisms to see whether predictions made hold true

The evidence for evolution includes the following: - the fossil record and transition fossils - biogeography - comparative embryology - comparative anatomy - biochemical similarities

Fossils

The fossil record shows a change from simple organisms in the oldest rocks to complex organisms in the youngest rocks

Transitional fossils have characteristics of different groups of organisms and therefore suggest a common ancestry (e.g. Archaeopteryx which shows characteristics of both birds and reptiles – it had feathers, beak and wishbone of a bird but showed some reptilian features like teeth in its beak, claws on its wings, unfused (free) bones in its ‘hand’ and a long jointed bony tail)

Similarity of fossils to present day organisms (e.g. number of fossils similar to modern day horse have been found and similarity in skeletons are best explained through common ancestry and evolutionary change according to environment and other factors)

Biogeography

The distribution of fossil and living plants and animals according to geographic regions is consistent with the theory that these organisms evolved from ancestral species within their geographic region (e.g. follows the theory of continental drift which is supported by fossil evidence)

Comparative embryology

The similarity of embryonic development suggests evolution from a common ancestor (e.g. the similarity of embryos across many vertebrates is a complex example of homology – structures of the embryo appear to be similar in anatomy but the structures carry out different functions as they develop into organs of the body)

Comparative anatomy

Homologous structures demonstrate common ancestry

Structures of organisms have similar anatomy but are adapted for a variety of functions (e.g. pentadactyl/forelimbs have similar basic structure in a number of different animals even if they serve completely different functions)

Biochemical similarities

All organisms share the same basic chemistry, they all: - consist primarily of organic compounds


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- share a common genetic code of DNA or RNA - rely on enzymes to control chemical reactions - share the same cell membrane structure - rely on respiration to make energy available for cellular processes (except chemosynthetic bacteria)

Amino acid sequences of proteins are more similar among closely related organisms than less closely related organisms (e.g. cytochrome-c is used to compare amino acid sequences, is a protein needed to make energy available in virtually all living things, on analysis it shows that the human sequence and monkey sequence are only different in one spot, i.e. one change in human DNA could produce the cytochrome-c of a monkey and therefore shows monkeys and humans are closely related)

PRACTICAL Perform a first-hand investigation or gather information from secondary sources (including photographs / diagrams / models) to observe, analyse and compare the structure of a range of vertebrate forelimbs Comparative anatomy

Comparative anatomy is the study of differences and similarities in the structure between organisms

Modern-day vertebrates are easily grouped into classes because they possess quite distinct features however, many have underlying similarities that suggest that they are more closely related than it appears

Pentadactyl limb (5-digit limb) – in evolved form, is found in many vertebrates and suggests they all have a common ancestor

The following diagram shows the pentadactyl limb of seemingly very different organisms but they all share similar structure – homologous structure with slight adaptations to suit their specific uses

PRACTICAL Use available evidence to analyse, using a named example, how advances in technology have changed scientific thinking about evolutionary relationships DNA hybridisation

DNA hybridisation is a process whereby the DNA of different species can be compared

The process uses heat to unwind and separate strands that make up the double helix. Segments of DNA from two different species are treated and then cooled together. On cooling hydrogen bonds form between the two single strands and the bonded section rewind forming a double helix again. Degree of bonding reflects the degree of base pairing between the two strands

The greater the number of hydrogen bonds between the strands, the greater the genetic similarity between the two species

This evidence provides support for Darwin’s theory where humans are considered to have evolved from apes


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Biochemical analysis – amino acids

This type of biochemical analysis compares the amino acid sequences of certain proteins between two different species, this can determine how closely related the species are

A protein found in haemoglobin, is often used for this analysis as it is common in a variety of organisms – cytochrome-c

Studies comparing amino acid sequences show that in one of the four chains, containing 146 amino acids is identical in chimpanzees and humans and 145 of the amino acids are the same in gorillas - further supports Darwin’s origin of man theory

Explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for divergent evolution and convergent evolution In 1858 Charles Darwin was nearing the end of his book “The Origin of the Species” which outlined his theory of evolution but at

this same time Alfred Wallace had independently developed a similar theory

Since Darwin was able to provide more comprehensive evidence for the theory, he is give greater credit than Wallace

They argued that some organisms possess characteristics more suited to their environment than others and were therefore more likely to survive and pass their characteristics on to their offspring. Gradually, over many generations, new organisms better adapted to their environment would evolve – this mechanism was called natural selection and also became known as ‘survival of the fittest’ (fitness in terms of natural selection not only refers to being healthy and well adapted to the environment but also to the reproductive capacity of the individual – e.g. mule is strong and well adapted but sterile)

Mendel had established the basic rules of genetics in the late 1850s but his work did not become well known until the turn of the century. Therefore Darwin did not know how characteristics were inherited. Nor did he known how the variations were essential for natural selection and evolution originated

Isolation

Isolation acts as a mechanism of evolution, allowing populations to evolve separately so that over a long period of time the separate populations no longer interbreed and thus become different species (e.g. Finches on the Galapagos islands)

Adaptive radiation

As organisms spread into new habitats, over millions of years they evolve, adapting to environments they inhabit – adaptive radiation (e.g. following the mass extinction of dinosaurs mammals adapted to occupy many vacant niches in ecosystems)

Divergent evolution

Divergent evolution is a consequence of adaptive radiation

Divergent evolution occurs when isolated populations of one ancestral species change over geological time to give rise to many new species, each of which show features that equip it to survive and reproduce under its particular selection pressures

Example: Darwin used the finches he found on the Galapagos islands to examine divergent evolution – beaks varied according to different selection pressures (the ability to crack nuts, or extract nectar etc) while coming from same ancestral background

Convergent evolution

Convergent evolution occurs over geological time when natural selection acts on distantly unrelated species to produce superficial similarities that are not due to shared ancestry but reflect the fact that the species are adapted to a similar way of life

Example: sharks and dolphins are similar in appearance but are not closely related. Similarity results from living in the same environment and being subject to similar selection pressures that favour streamlined shape for rapid movement through water

PRACTICAL Analyse information from secondary sources on the historical development of theories of evolution and use available evidence to assess social and political influences on these developments


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Historical developments of the theories of evolution:

1735 – Linnaeus published the classification system in which he classified apes and humans together. There was some idea of evolution in classification but the idea was strongly resisted

Late 1700s – Eramus Darwin (grandfather of Charles Darwin) first suggested that all life came from a single source

1809 – Lamarck put forward the first theory of evolution which suggested variation developed due to the ‘use’ or ‘disuse’ of body parts. These changes were passed to the offspring. His theory was proved incorrect but he challenged creationism and helped make Darwin’s ideas more acceptable

1859 – Darwin published the book On the Origins of Species by Means of Natural Selection and showed how the theory applied to humans in 1871 in the book Descent of Man

Early 1900s – Scientists refined Darwin’s theory Social and political influences on these developments:

Creationism was and still is the main barrier for the acceptance of evolution as certain religions believe that God created everything in six days and that organisms have not changed and are not related (mainly based around Christian beliefs which were very strong in the 19th century with the church also being political entity in many places)

In the 1920s Protestants campaigned against the anti-biblical ideas of evolution

Several states in the USA passed laws banning the teaching of evolution in public schools

2. Gregor Mendel’s experiments helped advance our knowledge of the inheritance of characteristics

PRACTICAL Perform an investigation to construct pedigrees or family trees, trace the inheritance of selected characteristics and discuss their current use Background:

A pedigree is a family tree showing a line of descent and is used to trace the occurrence of inherited traits in parents and offspring through a number of generations

By convention – circles represent females and squares, males. A line between a square and circle represents a union and a line down indicates offspring from the union

Filled in symbols represent individuals displaying the phenotype being studied

Pattern 1: - son and father are both affected - characteristic is dominant and therefore offspring must have at least one affected parent - heterozygous individuals will be affected - two affected parents can produce an unaffected child (both parents would be heterozygous)

Pattern 2: - daughter is affected but neither parent is - characteristic is recessive and the offspring are homozygous e.g. bb - both parents must be heterozygous (Bb) - heterozygous parents will be unaffected - two affected parents will always have an affected child

Pedigrees allow a pattern of inheritance to be traced throughout the generations of the family which can identify the probability of a child suffering from a certain genetic disease

Huntington’s chorea is an example of a dominant genetic disease:

Bb bb

Bb Bb

bb BB

Bb


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Cystic fibrosis is an example of a recessive genetic disease:

Outline the experiments carried out by Gregor Mendel

Gregor Mendel developed much of the early knowledge of genetics from breeding experiments with peas

An example of a characteristic he studied is the height of pea plants: 1. Mendel bred two groups of pea plants – tall and short, over a number of generations until all the offspring were identical to

the parents (they were pure-breeding plants), they were known as the P or parental generation 2. He crossed two groups by manually transferring pollen grains from one flower to another – the offspring were all tall pea

plants and were known as the F1 generation (F = filial = a son, in Latin) 3. Mendel then allowed the F1 generation to interbreed to obtain an F2 generation from which he obtained both tall and small

offspring in the ratio of three tall: one small – he obviously tested a great number but that was the simplified ratio

From his experiments he made two major statements which became laws of genetics: - The law of segregation: there are two factors or units in plants (called genes today) that control each

characteristic. In reproduction these two factors segregate, one factor appearing in every gamete which recombine at fertilisation, they do not merge but remain separated

- The law of independent assortment: when the pairs of factors segregate, they do so independently of the other pairs of factors. They are distributed into gametes independently of other pairs of factors (now we know that this law applies in all cases except where genes are situated on the same chromosome. It is chromosomes and not genes that separate and are distributed independently)

Some factors (genes) are dominant, that is, they alone are expressed in the presence of another recessive gene

It is possible to predict the numbers and types of offspring by performing a large number of crossing experiments as Mendel did

Describe the aspects of the experimental techniques used by Mendel that led to his success The success of Mendel’s experiments on the pea plants in his garden from which he could obtain results for analysis and

predictions is due to five factors: 1. He studied a large number of characteristics in the plants 2. He carried out a large number of crosses 3. He used pure breeding lines 4. He made exact counts of characteristics, which produced quantitative data that could be analysed simply 5. Previous researchers studying heredity had investigated the whole plant or animal – Mendel studied separate, identifiable

characteristics that occurred in pairs (e.g. round or wrinkled seed, purple or white flower, tall or short plant height)

Bb

BB

Bb

bb

Bb

bb

bb


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Describe outcomes of monohybrid crosses involving simple dominance using Mendel’s explanations PRACTICAL Solve problems involving monohybrid crosses using Punnett Squares or other appropriate techniques A monohybrid cross is mating between two parents in which only one pair of genes, that is one characteristic, is considered

A Punnett square is a grid that can be used when making monohybrid crosses – Mendel used this to explain the crosses and work out the ratios of the genotypes and phenotypes

Example: a black hybrid guinea pig has the genotype (Bb) where the black gene (B) is dominant and the white gene (b) is recessive. Two hybrid black guinea pigs were mated (Bb X Bb)

BB: Bb: bb black: white 25%: 50%: 25% 75%: 25%

The results for crossing experiments are bases on probability. They give predictions for large numbers of offspring but do not give the order in which the offspring are produced

Distinguish between homozygous and heterozygous genotypes in monohybrid crosses Distinguish between the terms allele and gene, using examples Explain the relationship between dominant and recessive alleles and phenotype using examples Genes are situated on chromosomes, each gene may be represented as a band on the diagram of a chromosome. In a double-

stranded chromosome, each gene is represented twice, opposite each other, which allows for division at mitosis

Chromosomes occur in pairs (except meiotic cells – gametes) corresponding pairs are called homologous chromosomes

Along each member of the homologous pair are corresponding pairs of genes which are called alleles. Alleles are not necessarily identical but they code for the same characteristic (i.e. one allele may be dominant to the other, explained below)

When alleles are different – heterozygous, when alleles are same – homozygous (individual pure-bred for that characteristic)

One allele may be dominant over the other in heterozygous individuals. The non-dominant gene allele is recessive. The dominant allele’s character is always expressed but the recessive allele is only expressed in the absence of the dominant one

Genotype (remember GENE) is the actual pair of genes containing information for a characteristic. E.g. Bb is the genotype

Phenotype (remember PHYSICAL) is the physical appearance, the observable characteristic that results from the genotype. E.g. Bb and BB both produce black guinea pigs, they have the same phenotype but different genotype

PRACTICAL Process information from secondary sources to describe an example of hybridisation with a species and explain the purposes Hybridisation

Mendel’s model provided scientists with ideas that could be used to improve agricultural crops by carrying out systematic crosses between different varieties of one species to form hybrids that had new combinations of desirable characters

There are two different types of hybridisation but both aim to create new and better combinations of characters: 1) crossing different varieties of one species to produce new varieties 2) crossing different but closely related species

B b

B BB Bb b Bb bb


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Hybridisation does not always create improvement. In hybridisation between species, hybrid organism may be unviable (unable to survive) or infertile (sterile – as in mules which are a cross between a horse and a donkey)

Hybridisation or crossbreeding has been used with commercial animals to increase yields. For example, in beef cattle, increased birth weights have been observed in hybrid calves from the crosses of two different breeds such as Hereford x Angus, compared with true breed crosses such as Hereford x Hereford. Birth weights increased further when these hybrids were outcrossed with yet another breed ((Hereford x Angus) x Shorthorn)

In many cases, true-breeding lines carry some deleterious alleles. When two different lines are crossed, the process of hybridisation introduces favourable alleles into the resulting F1 hybrids. If the favourable alleles are dominant they will mask the deleterious alleles but if they are recessive they will not be expressed until the F2 or later generation)

In the late 19th and early 20th century William Farrer pioneered Australian wheat research using systematic crossbreeding to improve bread wheat. The first wheat to be grown in Australia was an old English variety that ripened too late to survive hot summers and was affected by fungal diseases. By carrying out artificial crosses he produced wheat that had properties like:

- earlier ripening to suit the shorter growing season in Australia - improved baking quality - improved yield (grams per head) - resistance to the fungal disease known as bunt

In general, hybrid plants are more vigorous and higher yielding compared with true-breeding parents – called hybrid vigour

Outline reasons why the importance of Mendel’s work was not recognised until some time after it was published Its not certain why Mendel’s finding were ignored but here are some possible reasons:

Mendel only presented his paper to a small number of scientists, and has his work was radically different from previous research, they may not have understood it

Mendel was not part of the established scientific community, he was a monk who worked quietly in a monastery with assistants

Mendel’s work used statistics and mathematical calculations and applied these to genetics, other scientists may not have been able to understand these calculations, they were scientists not mathematicians

3. Chromosomal structure provides the key to inheritance Outline the roles of Sutton and Boveri in identifying the importance of chromosomes In 1896, Boveri crossed two different species of sea urchins. He found that the resulting hybrid larvae had characteristics of

both parents. He then collected eggs from the first species of sea urchin and vigorously shook the eggs so that they became enucleated fragments. He then mixed these fragments with sperm from the second species. The resulting larva showed no characteristics of the female parent and he therefore concluded that inheritance was due to “something” present in the nucleus and that this “something” was absent from the cytoplasm

Sutton used the research of many other scientists; he synthesized all their research. He recognised that chromosomes provided a mechanism for the operation of Mendel’s laws and could account for the properties of Mendel’s factors, such as the segregation of alleles and the independent assortment of genes

Boveri’s and Sutton’s study of the behaviour of chromosomes led to the realization that: - genes are part of chromosomes

- the behaviour of chromosomes in meiosis explains the segregation and assortment of genes Explain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes Explain the role of gamete formation and sexual reproduction in variability of offspring There are two laws of genetics to describe the segregation and recombination of genes (which Mendel theorized)


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- The law of segregation there are two genes that control each characteristic, during reproduction these two factors segregate with one factor appearing in every gamete. The factors recombine at fertilization – they do not blend, but match together

- The law of independent assortment when the pairs of factors segregate they do so independently of the other pairs of factors, they are distributed into gametes independently. This law applies in all cases except where genes are located on the same chromosome – the chromosomes (not the genes) separate

Genes on the same chromosome do not always assort independently of each other – Mendel did not detect this

Corresponding pairs of chromosomes may intertwine during meiosis, break and rejoin so that parts of different chromosomes are switched over – this is crossing over

Crossing over results in increased genetic variation in the offspring – Mendel was not aware of crossing over

Crossing over results in the exchange of genes between homologous chromosomes

The re-assortment of genes and segregation of alleles to produce new genetic combinations is known as recombination and is a major cause of variation in offspring of the same parents

Meiosis and sexual reproduction cause variation in a species population

PRACTICAL Process information from secondary sources to construct a model that demonstrates meiosis and the process of crossing over, segregation of chromosomes and the production haploid gametes

Human body cells contain the diploid number of 46 chromosomes

Egg and sperm cells each have 23 chromosomes, where 23 denotes the haploid number

Meiosis is the process that produces gametes with half the number of chromosomes seen in somatic cells and is the precursor cell to the gametes

After fertilization, when the egg nucleus and sperm nucleus fuse, the diploid number of chromosomes is restored

In most animals, meiosis occurs in the ovaries of females and the testes of males

In plants, meiosis occurs as part of egg and pollen formation

When gametes are produced by meiosis two features are seen: - each gamete contains only one member of each homologous pair of chromosomes - any member of one pair can be found with any member of another pair of chromosomes

Meiosis halves the chromosome number but some chromosomes come out of the process spliced with part of their homologue – this is a result of crossing over


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Describe the chemical nature of chromosomes and genes

A chromosome is made up of 40% DNA and 60% protein (histone)

Short lengths of DNA make up genes so genes have the same composition as DNA (nucleotides, see next dot point)

Identify that DNA is a double-stranded molecule twisted into a helix with each strand, comprised of a sugar-phosphate backbone and attached bases, adenine (A), thymine (T), cytosine (C) and guanine (G), connected to a complementary strand by pairing the bases, A-T and G-C The genetic material DNA is a complex molecule built from many basic building blocks called nucleotides

There are four different kinds of nucleotides found in DNA, but they all have a sugar (deoxyribose) part, a phosphate part and a nitrogen-containing base. The four different bases are adenine (A), thymine (T), cytosine (C) and guanine (G)

There are complementary base pairing, A-T and G-C – the resulting DNA molecule is a ladder-like double helix strand

Phosphate P P

1. Starting point: cell with two pairs of single stranded homologous chromosomes

(diploid number: 2n = 4) 2. Early in meiosis, each chromosome replicates to become double stranded 3. The homologous chromosomes align and pair closely or synapse. One or more

exchanges or crossovers occur between a matching segment of one chromosome with a strand in its paired homologue. Crossing over produces new combinations of genetic instructions. The chromosomes then line up across the equator of the cell. Different arrangements are possible

4. The homologous chromosomes separate (disjoin) from each other when their

centromeres are pulled to opposite poles. The disjunction of each homologous pair is independent of any others. (e.g. if the red chromosome goes to the left hand side this does not influence which of the longer chromosomes will go to the right)

5. The resulting two products each have two double stranded chromosomes, one long

and one short 6. The strands of each replicated chromosome disjoin so the single stranded

chromosome moves in opposite directions. The separation of the single stranded copies of each chromosome is independent of that of other chromosomes

7. End point: typically, four cells result from meiosis with each end product containing

the haploid number of chromosomes (started with 2n=4, process produces four cells each with n=2)

8.


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Describe the inheritance of sex-linked genes, and alleles that exhibit co-dominance and explain why these do not produce simple Mendelian ratios

Explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance Incomplete dominance

Not all genes show dominance and recessiveness. Sometimes neither gene dominates, both are expressed in the presence of each other – incomplete dominance

Example: snapdragons – pink flowers are a result of there being a gene for red pigment and a gene for white pigment, neither is dominant or recessive and are hence both expressed

Co-dominance

Co-dominance occurs when both alleles are present but there is no blending effect

Example: roan cattle have patches of red and white as a result of both genes being expressed separately without blending

Mendel only chose characteristics that showed dominance and recessiveness, otherwise it would have been too difficult to interpret results with their primitive knowledge of genetics

Sex linkage

Sex is genetically determined – females have two X chromosomes and males have an X and a Y chromosome

Sex linked genes are those located on the sex chromosomes, usually the X chromosome has the gene and the Y chromosome does not, this gives a unique pattern of inheritance

Haemophilia (disorder where blood does not clot meaning a cut may risk bleeding to death) and colour-blindness (inability to distinguish between certain colours) are both due to a sex linked trait in humans. They are due to the recessive allele of a gene on the X chromosome. Being recessive, if present in a female but she also has the dominant allele the recessive trait is not expressed. However as males only have one X chromosome, if the recessive allele is present the trait is expressed and this explains why more men suffer from these two disorders than females

PRACTICAL Solve problems involving co-dominance and sex linkage Solve problems by using strategies such as Punnett squares to develop a range of possible outcomes for a particular problem

Example: In a cross where neither parent is colour-blind but the mother is a carrier for the condition what is the chance of: (a) a male child being colour-blind (b) a female child being colour-blind

The gametes are found for each parent then combined using a Punnett square to determine the genotype of the offspring. From the above results, there is a 50% chance a male child will be colour-blind but no chance for colour-blindness in a female child. However, 50% of the female offspring will be carriers

Describe the work of Morgan that led to the understanding of sex linkage Morgan bred fruit flies and noticed a male fly with white eyes among the offspring of red-eyed parents. He decided to

investigate by breeding this fly with normal, red-eyed females. All of the F1 generation had red eyes. However, when the F1 generation bred the F2 generation contained some white-eyed flies and all of them were males. Morgan hypothesized that the white-eyed characteristic was sex-limited and that the genes for sex-limited characteristics were on the X chromosome

Sex linkage means that info for some non-sexual characteristics is found on the X chromosome. This is a problem when genetic deficiency occurs, especially in males. If there is a deficiency, it is usually on the X chromosome. Females, have two X

XNY / XNXn XN Xn

XN XNXN XNXn

Y XNY XnY

Sugar Base A T


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chromosomes so have a 2nd normal gene to fall back on (it is rare that both alleles are deficient) but males only have one X chromosome the result is a deficiency which is sex-linked

Example: haemophilia – the gene that controls the synthesis of an important factor that contributes towards blood clotting is situated on the X chromosome. In males where this gene is deficient, an insufficient amount of blooding clotting factor is made so bleeding can not be stopped. Nowadays the clotting factor can be synthesized and supplied to sufferers. Females are more usually carriers of the defective gene as it is very rare for two defective genes to be present in a female. Female carriers have a 50% chance of passing the gene to their sons, so it is a much more common condition in males

Outline ways in which the environment may affect the expression of a gene in an individual The environmental factors which may influence the expression of a gene in an individual include:

- nutrition/diet - socio-economic background - oxygen deprivation at birth - peers - traumatic event such as deaths or accidents

Example: many Australian children have genes for medium length bones and strong muscles whereas North African’s genes code for longer bones and less muscle. The Sydney boy will be more likely to achieve the maximum bone length and muscle strength allowed for by his genes, and therefore more likely to fulfil his genetic potential and this is because the Sydney environment is more favourable than that of North Africa. For optimum growth many substances must be synthesized inside the body and therefore is controlled by the presence of raw materials like diet

PRACTICAL Identify data sources and perform a first-hand investigation to demonstrate the effect of environment on phenotype Background: Hydrangea plants produce blooms that vary depending on the acidity or alkalinity (pH) of the soil in which they are growing. The colour is due to pigments known as anthocyanins which are located in membrane-bound sacs within the petal cells Aim: To demonstrate the effect of environment on phenotype Method:

1. Acquire six hydrangea plants each of similar size, age and all of same species, obtain specimens currently in bloom 2. Pot each in an identical fashion with equal amounts of the same potting mix and equal amounts of sunlight and water 3. To three add a small quantity of acid to the water – make sure it is not too concentrated 4. To the other three add a small quantity of a base/alkali to the water – again making sure it is not too concentrated 5. After a few days of watering record any changes in the plant, play special attention to the flowers

Results: The plants with acidic soil will have bright blue flowers while the plants in basic/alkaline soil will have pale pink or off-white flowers Conclusion: The acidity of the soil is an environmental change that changes the colour of the flowers (phenotype). To further test this, a larger experimental group maybe used but will still yield the same results


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4. The structure of DNA can be changed and such changes may be reflected in the phenotype of the affected organism

Describe the process of DNA replication and explain its significance DNA replication is the conversion of single-strand chromosomes to double-stranded chromosomes in a living cell at between

one mitosis and the next – during mitosis double-stranded chromosomes divide into single-stranded chromosomes

Enzymes unravel the double helix slowly, nucleotides containing complementary bases line up along each polynucleotide and the bases attach to form two new double helixes that are carbon copies of the original

DNA replication occurs between gamete formation and the growth of a new organism after fertilization – this is necessary because when gametes are made (in meiosis), they have single stranded chromosomes

Outline, using a simple model, the process by which DNA controls the production of polypeptides PRACTICAL Perform a first-hand investigation or process information from secondary sources to develop a simple model for polypeptide synthesis

All genes (DNA) contain coded information in the form of a base sequence, for most genes the coded information is a set of instructions for the joining of amino acids to form polypeptides and proteins

Initially DNA molecules unzip and the DNA is transcribed into the single stranded mRNA molecule

Messenger RNA (mRNA – single strand of nucleotide bases with ribose sugar and the thymine replaced by uracil) is an intermediary in this information flow and carries the information from the DNA to the cytoplasm

The coded DNA is first transcribed to RNA and then translated into a specific sequence of amino acids in a polypeptide

The information in some genes does not result in the output of proteins, these genes produce other kinds of RNA such as transfer RNAs (tRNA) and ribosomal RNAs (rRNA)

In this case the RNAs formed are not an intermediate step but end products: - tRNAs are the carrier molecules that transport amino acids to ribosomes - rRNAs form part of the structure of ribosomes and cell organelles where translation occurs

Explain the relationship between proteins and polypeptides A chromosome is a large DNA double helix with protein attached

Information in

DNA

transcription Information in

mRNA

translation Amino acid sequence in polypeptide

Information in

DNA

Information flow tRNA and rRNA

end products


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Genes are situated along chromosomes, a gene is a length of DNA containing info for synthesis of a specific polypeptide

A polypeptide is a long chain of amino acids that makes up a protein and may be coiled in a particular arrangement in space

PRACTICAL Analyse information from secondary sources to outline the evidence that led to Beadle and Tatum ‘one gene – one protein’ hypothesis and to explain why this was altered to ‘one gene – one polypeptide’ hypothesis

In the 1940s Beadle and Tatum used bread mould to investigate nutritional mutations. Using X-rays, they produced mould that was unable to produce a specific amino acid, the mould was unable to grow unless the amino acid was added

They showed that genes controlled biochemical processes and hypothesised that for each gene there was one protein

The enzymes that they studied consisted of one polypeptide but many more complex enzymes (proteins) exist and consist of chains of polypeptides so the hypothesis has been changed to the “one gene – one polypeptide” hypothesis

Explain how mutations in DNA may lead to the generation of new alleles

A mutation is a change in a gene – it involves some change in the base sequence of the DNA composing the gene. It can be a substitution of one or more bases for others, deletion of bases or insertion of bases

Gene mutation produces new alleles of genes in various species and so generates genetic variation

If the mutation takes place in an essential part of the gene, the protein specified by the gene will also be altered

Example: sickle cell anaemia is caused by the substitution of only one base in the DNA

Many proteins are enzymes that catalyse chemical reactions. Mutation affect chemical reactions due to the changed sequence

Example: albinism – a mutation (altered gene) causes the production of an altered enzyme for synthesizing the skin pigment melanin. Albinos are characterised by pale skin and pink eyes, they have increased susceptibility to skin cancer

Discuss evidence for the mutagenic nature of radiation

Rate of mutation can be increased by certain environmental factors called mutagens - some chemicals, X-rays and UV light

Some mutations are believed to be changes in the genes that control cell division and this can result in cancer

The Chernobyl nuclear accident in Ukraine (1986) increased the incidence of cancer and is believed to peak in 2005. The radioactive material continues to spread, usually by floodwaters into reservoirs and catchments of neighbouring countries

PRACTICAL Process information to construct a flow chart that shows that changes in DNA sequences can result in changes in cell activity

If there is a substitution for a single base pair on a DNA strand such as a G-C replaced by A-T, then this results in a changed amino acid codon forming a different polypeptide. If one base pair is lost from the sequence there will be a shift along the DNA molecule producing different polypeptides

The following flow chart shows the reaction if thymine is lost from the start of a DNA sequence:

DNA ACG TCT ATT TGC GAC GTA TT

Functional enzyme

UGC AGA UAA ACG CUG CAU AA

Dysfunctional enzyme

mRNA

Amino acid

polypeptide

TAC GTC TAT TTG CGA CGT ATT

AUG CAG AUA AAC GCU GCA UAA

met gin lie asn ala ala stop

cis arg stop


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Cell activity is controlled by enzymes which are formed from chains of polypeptides. If the chain of amino acids forming the polypeptide is not in the right sequence, then the enzyme formed will not be functional and may even stop prematurely

Explain how an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection

Mutations may be an advantage or a disadvantage to organisms- usually unfavourable. They occur naturally as errors when genes are copied, so there is a small %age of natural mutations in a population for every gene. Mutations are believed to have a significant role in evolution, those favourable produce variations that may be naturally selected, resulting in evolution

Darwin knew that characteristics were passed from one generation to the next but did not know the mechanism. Mendel showed characteristics were inherited as ‘genes’. Boveri and Sutton recognised chromosome behaviour explained how genes are inherited. DNA proved to be the material that coded for each gene – DNA is passed from one generation to the next

Darwin knew that variation within a population was essential for natural selection to operate but did not know the source. DNA codes for characteristics. Thus changes in the DNA sequence, mutations, cause variations that may be inherited

PRACTICAL Process and analyse information from secondary sources to explain a modern example of ‘natural’ selection

Some organisms like bacteria produce large numbers of offspring of which some may carry genes that give them resistance to antibiotics. These individuals are able to survive and reproduce with reduced competition from other members of the same species and hence each generation produces a greater number of these resistant individuals. This is the dilemma that medical experts are facing as antibiotic resistant strains of bacteria become more common and antibiotics become less effective

A similar situation occurs with insects and insecticides - the adaptations increase the organisms chance of survival and hence the frequencies of these genes in the population increase – “survival of the fittest”

Describe the concept of punctuated equilibrium in evolution and how it differs from the gradual process proposed by Darwin Darwin proposed that evolutionary change occurred gradually over thousands of years – but in the 1970s the theory of

punctuated equilibrium was proposed

Punctuated equilibrium states that most species adapt until they reach a stable stage and are in a state of equilibrium with their environment. This equilibrium may last millions of years but may be punctuated by rapid evolutionary change (in terms of evolution rapid means thousands of years)

The concept of punctuated equilibrium helps explain why the fossil record is incomplete, if evolutionary change happens in a short time span then the intermediate forms would not be around long enough to become fossilized and it becomes almost impossible to pinpoint this change in ancient layers of rock

PRACTICAL Process information from secondary sources to describe and analyse the relative importance of the work of:

- James Watson - Francis Crick

- Rosalind Franklin - Maurice Wilkins

in determining the structure of DNA and the impact of the quality of collaboration and effective communication in scientific research

Scientific discoveries are rarely the work of one person but tend to result from teams of people bringing together different skills. The teams maybe working or may be scattered around the world working independently in different laboratories

Rosalind Franklin and Maurice Wilkins were from King’s College London while James Watson and Francis Crick were from Cambridge University. Rosalind Franklin was a woman working in a male dominated field. Her work using X-ray crystallography showed DNA had characteristics of a helix and she wished to gather more evidence of this result. However Maurice Wilkins showed her results to Watson and Crick without her permission or knowledge. This info was enough to


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encourage Watson and Crick to develop their model of the double helix for the structure of DNA. Rosalind Franklin was given no recognition for her work. She died in 1958 and Watson, Crick and Wilkins received Nobel prizes for their work in 1962

5. Current reproductive technologies and genetic engineering have the potential

to alter the path of evolution Identify how the following current reproductive techniques may alter the genetic composition of a population:

– artificial insemination – artificial pollination – cloning

It is advantageous for a population of organisms to maintain genetic variability, as it provides the opportunity for natural

selection to operate and for the population to evolve and survive

Many organisms have adaptations promoting genetic diversity like: - cross-pollination and fertilization - meiosis and the crossing over of chromosomes

Humans often want to breed organisms with desirable characteristics and this is done by artificial selection or selective breeding – organisms with desirable traits are chosen and mated

Two techniques used in artificial selection are: - artificial insemination - artificial pollination

Artificial insemination

Artificial insemination (AI) involves collecting the sperm from a male and inserting it into the vagina of a female. The sperm swims to the egg, which is fertilized

AI is useful in breeding because: - it increases the chance that sperm from the selected male fertilizes the egg of the selected female - it can be used when it is difficult or costly to bring the female and male together - the sperm used can be frozen in liquid nitrogen and transported across the country or around the world (i.e. a

prized English bull can be bred with a prized Australian cow without having to transport either animal)

One disadvantage of AI is that it reduces the chance of random crosses and hence reduces genetic variability in the population

AI is also practiced by humans – sperm banks have been established to keep and collect sperm (the characteristics of the male are recorded and the female may choose the sperm from a male whose characteristics seems desirable to her). This practice allows the woman, in couples in which the male is sterile, to have children


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Artificial pollination

In plants, plant breeders use artificial pollination (AP) to breed plants with selected characteristics

Mendel used AP to ensure the right crosses occurred in his experiments

In AP, the pollen from the male anther is brushed onto the female stigma and the pollinated flower is then covered to prevent pollination from other flowers. This technique is especially advantageous in the breeding of strains of plants

AP reduces genetic diversity if it is used to breed a population of plants with the same set of similar desirable characteristics Hybrids

Selective breeding produces organisms that are homozygous for many genes. This is disadvantageous as organisms that are homozygous for many genes are usually less vigorous than those that are heterozygous for many genes. And if homozygous for many genes then there is a greater chance that it will display a disadvantageous characteristic due to a pair of recessive alleles. This problem is sometimes overcome by hybridisation

Hybridisation is when two different strains of plants or animals are interbred to produce a hybrid strain

Example: the most productive strain of sugar cane is a hybrid of noble cane (produced large amounts of sugar but was very susceptible to disease) and wild cane (produced almost no sugar but was very resistant to disease). The resulting hybrid produced large amounts of sugar and was disease resistant

The only disadvantage of hybridisation is that hybrids are heterozygous for many genes and the next cross has 50% chance of forming homozygous offspring, relate to above

Cloning

Selective breeding can produce populations with desirable characteristics but as it relies on sexual reproduction some genetic variability is always likely to occur as a result of meiosis, random assortment of chromosomes and crossing over

Often horticulturalists want to reproduce plants that are not just similar but genetically identical. This can be done by cloning – cuttings from parent stock are planted out. This has advantages for the farmer as the plants have identical requirements and under the same environmental conditions grow in similar ways to produce similar yields at about the same time. However as these cloned crops are identical every organism in the population is susceptible to the same diseases. This means if a disease breaks out it spreads rapidly, devastating the population without any potential for the natural selection of immune varieties

While cloning in plants had been practiced for thousands of years, the cloning of complex animals had proved difficult

In 1998, a team of Scottish scientists led by Ian Wilmot cloned a sheep (Dolly) from a cell taken from a sheep’s mammary gland. They destroyed the nucleus of an egg cell and replaced it with the nucleus taken from the mammary cells of an adult sheep. The egg cell with its new donor nucleus developed into a sheep with an identical genetic makeup to its parent

Cloning is an expensive process with limited advantages over other reproductive techniques. At present cloning in mammals is unlikely to be used extensively for reproduction because it is expensive and difficult. Cloning in mammals is more likely to be combined with other biotechnology to produce cloned organs and tissues for use in transplants

PRACTICAL Process information from secondary sources to describe a methodology used in cloning

Cloning is the process of making genetically identical copies of an organism without using the process of sexual reproduction – both plants and animals have been successfully cloned

Cloning plants

Recently, plants have been cloned using tissue culture propagation. Tissue from the roots is taken and the root cells separated. These cells are then grown (cultured) in a nutrient-rich medium where they become unspecialized (the unspecialized cells are called calluses). After treatment with the appropriate plant hormones the calluses develop into seedlings that go on to grow into fully mature plants that are genetically identical to their ‘parent’ plant

Rare orchids have been cultured using this technique. The Wollemi Pine has also been cloned to preserve the species Cloning in animals

Progress in cloning animal species has not been as rapid as in plants


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Current techniques require an unfertilized egg cell acting as a ‘host’ for genetic material from a specialised cell. The donor cell is enucleated and the nucleus from the cell species to be cloned is inserted. An electrical stimulus is used to fuse the nucleus with the egg cell and stimulate cell division. At a certain stage in cell division, the embryo is introduced into the surrogate mother where it continues its development. When born, offspring is genetically identical to the animal that donated the nucleus

Outline the processes used to produce transgenic species and include examples of this process and reasons for its use With development of new technologies in biotechnology scientists can now introduce genes directly from one organism to

another. This is done by removing a gene from one organism and injecting it into the egg of another. The gene then becomes part of the egg’s DNA. The egg develops into an organism that has the injected DNA within its cell nuclei. When the gene is injected into a different species the new organism is called transgenic

Various techniques exist for transferring DNA into a host cell, they include: - micro-injection of the DNA of a gene - transfer using a virus to carry the DNA of the gene (viral vector) - use of an electric pulse (electroporation) - use of ballistics (the ‘gene gun’)

The specific genes are isolated by one of the following methods: - isolating it from chromosomal DNA - chemically synthesizing it from nucleotide sub-units - making a copy of it from a template

Example: In Scandinavia farmers experience difficulty in growing strawberries. A transgenic strawberry has been developed that contains a gene from salmon. The transgenic strawberry is able to grow better in the cold

Example: The quality of sheep wool is enhanced by the presence of an amino acid called cysteine. Sheep can not synthesise cysteine so scientists are developing a transgenic sheep that has the gene for cysteine production in it from alfalfa plants. Once introduced the sheep will grow and breed passing the trait on

The production of transgenic species has a number of advantages: - genes responsible for a single desired characteristic can be transferred across species - human material can be produced in transgenic species so disease maybe treated by a special milk from a

transgenic cow

However while there are advantages there are many ethical and practical concerns

Discuss the potential impact of the use of reproductive technologies on genetic diversity of species using a named plant and animal example that have been genetically altered Genetic engineering, especially in the production of transgenic species has the potential to increase the genetic diversity of a

species. However it may also lead to the decrease of genetic diversity as the crops developed may produce higher yields and farmers wanting to compete may have to grow these ‘superior’ crops in order to make a profit

Example: in Australia and USA tomatoes have been genetically engineered to have long shelf-life and excellent taste

Example: salmon have been genetically modified (using bGH – bovine growth hormone) so that they grow bigger than normal salmon. Female salmon are attracted to and mate more often with larger males. If the transgenic salmon where to escape into the wild population then wild females would prefer to mate with the larger transgenic males and the transgene would spread rapidly in the natural population

PRACTICAL Analyse information from secondary sources to identify examples of the use of transgenic species and use available evidence to debate the ethical issues arising from the development and use of transgenic species Transgenic organisms have DNA derived from other species incorporated into their genome – done by genetic engineering

techniques. Both plants and animals have been modified in this way to create ‘improved’ strains of a particular species

Ethical concerns include:


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- Man is tampering with nature too much - Side-effects of GE foods are still unknown and are being eaten without proper research and testing - There are major drawbacks if these implemented genes cross over to wild species and there is possibility of

massive detrimental effects to ecosystems

For examples of transgenic species look at the above two dot points

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Biology Notes, Module 2, Blueprint of Life, by F.A ... · Biology Notes, Module 2, Blueprint of Life, by F.A 4 | P a g e because of the rate in which they reproduce. Economically