Variation and Selectionvariation

Objectives:*State the differences between continuous and

discontinuous variation**Identify and explain the examples of variation

*** Differentiate between inherited and environmental variations

Home work: due in on 25/10Describe how you would investigate the effect of an environmental variation on the growth of plants of genetically identical nature. Give full practical details that ensure that you have designed a valid investigation.

Starter• In what ways are these people different?• Which characteristics are due to genetics and

which are environmental?

We are similar to chimps and monkeys in many ways but we are significantly different from them. This is why we do not belong to the same species.

In Biology variation means :

•Differences between species – used in constructing keys•Differences within a speciesWe will concentrate only on the second point here as we have looked at the first in classification unit.

There are ……. types of variation within a speciesThey are :

Discontinuous variation

Discontinuous variations are entirely genetically controlledThey cannot be altered by external conditions.

You are either male or female, there are no intermediates

Your ABO blood group is either A, B, AB or O

Genetic defects such as colour blindness, albinism,achondroplastic dwarfism, sickle cell anaemia are all genetically controlled and expressed in a discontinuous way

You either have these conditions or you do not. There are no intermediate states. Data about such variations can only be plotted as ------ Other examples of discontinuous variations are:

Discontinuous variation

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percentagein populationof Britain

Discontinuous variation in blood group. The figures cannotbe made to fit a smooth curve because there are no intermediates

Blood groups

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Continuous variation describes the situation in which there area great many intermediates between the extremes and there are no clear divisions between the intermediates .

For example, there is a range of heights in this class. If you divide the class into groups. People do not belong to one or other of a small number of distinct categories.If you are divided into groups (e.g. !65cm -170cm etc) you can plot a frequency histogram. Mean height will be in the middle of the range corresponding to the group with largest number of you

Variations such as these are under genetic control but there are several pairs of genes involved.

The genome AA BB CC DD might give tall feature while the genome aa bb cc dd might be responsible for shortness.*

Genomes AaBbCcDd or AABbCCdd or aaBBccDd and all the other possible combinations would give intermediate heights

Continuous variation16

Hair colour variation

There are as many categoriesof hair colour asthere are children

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Continuous variation also occurs when the characteristicsare controlled by the genes and the environment

Your height will depend on the genes you inherit and on the amount of food you eat during your growing period, or exercise you do, or the age that you go through your growth spurts.Other examples can be length of your index finger.In plants it can be length of leaves.

The next slide shows the range of heights of army recruits

Continuous variation

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thousandsof men

height in inches

There seem to be distinct categories of height but this is becausemeasurements are made to the nearest inch

Graph of heights

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If measurements could be made to the nearest millimetrethere would be a smooth transition in the heights

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This is how continuous variation would appear in a graph

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Inheritance vs Environment16

Identical twins .Just how identical are they?

Identical twins separated at birth.Just how different are they?

Mexican hat plants asexually reproduce to make lots of tiny plantlets around the leaves. You can detach them grow them as individual plants . Any variation you see wil be …………………

Inherited variations result from the activity of genesThey are genetically controlled

Genetically controlled variations cannot be altered

For example, hair colour, skin colour*, blood group,finger prints and sex cannot be changed naturally

Acquired & inherited

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Mutations

Objectives:*Define the term mutation and describe Down’s syndrome as an example of mutation**Describe the possible effects of radiation and certain chemicals on the rate of mutations***Describe sickle cell anaemia as an example of mutation

Starter: Make two lineshttp://biology-animations.blogspot.com/2011/07/genetic-mutation-animation.html

Mutation• Mutations cause new forms of genes.• They alter the sequence of the DNA.• Most mutations are spontaneous or natural and only present

in body cells (eg) skin cells, nerve cells, red blood cells.• However some mutations are present in the reproductive cells,

sperm and egg cells.

• These mutations can be inherited and so passed on to the person’s offspring.• Some mutations occur completely spontaneously, but some are caused by:

– U-V light– Exposure to x-rays– Exposure to radiation– Exposes to certain chemicals(BENZPYRENE in cigarette smoke)

Result in body cells-cancer, in sex cells variations in offspring

A mutation is a spontaneous change in a gene or Chromosome that may cause a change in phenotype. Somecan be harmful, some beneficial and some have no effect Gene mutations may arise when a gene fails to make an exactcopy of itself during replication prior to meiosis or mitosis. Eg. Eye colour in fruit fly.

Chromosome mutations can result from: Damage to, or loss of a chromosome

Incomplete separation of chromosomes at meiosis leading to extra chromosomes in one gamete Part of a chromosome becoming attached to another chromosome (translocation) Doubling the whole set of chromosomes

Mutations14

MutantAlbino a mutation for gene controlling melanin production

Chromosome mutations in humans usually result in spontaneous abortion of the foetus But a proportion survive e.g.

Downs syndrome. The affected person has one extra chromosome in their genome (i.e. 47 instead of 46 chromosomes) This happens during meiosis when an egg cell is formed .In egg the 21st chromosome doesn’t separate properly causing an egg with 24 chromosomes.

This results in characteristic facial features, varying degrees of mental impairment and, usually, a very cheerful disposition

Klinefelters syndrome. The affected male has an extra X chromosome (XXY)

The person appears to be a normal male but he is infertile

Chromosome mutations in humans

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Gene mutations often arise as a result of damage to or faulty replication of DNAIf a nucleotide is not copied accurately, the triplet which containsthe fault will not code for the correct amino acid

A protein with an incorrect amino acid will not function properly If the protein is an enzyme, this means that the enzyme will not workThe cell chemistry will be disrupted if an essential enzyme failsto function normally This means that most gene mutations have a damaging effecton the cells and the whole organism.

Gene mutations23

Sickle cell anaemia(inherited)Inherited diseases are caused by faulty alleles, most of which are recessive

People with SCA are homozygous(HsHs) for this allele. However heterozygous people (HsHN) are carriers of the disease and have no problems but they are resistant to malaria as parasites can’t enter their RBC which is a mutation favoured by nature . The alleles are codominant (incomplete dominance) so heterozygous RBCs are a mixture of both.1. What is the probability of children getting SCA if both parents are heterozygous?

1 in 4 or 25%

Natural Selection

Objectives:*Describe how the best adapted individuals survive to pass on their genes to their offspring**State that competition leads to differential survival

Starter:What is natural selection?Use the first objective to answer

The process by which organisms well adapted to their environments have a greater chance to breed and pass on their genes to the next generation than those that are less well adapted.

h/w due in on 31/10

The factors for natural selection:VariationOver – populationCompetition leading to differential survivalAdaptationEvolution

Variation

Caused by gene mutation . Some are advantageous to the individuals that expresses them e.g. camouflage

Caused by sexual reproduction. During meiosis the alleles of different genes are reshuffled to give new combination in the gametes. During fertilisation alleles from two different individuals are combined in the same nucleus

Over-population: How does it help in natural selection?

In spite of plants and animals producing millions of gametes many of which get fertilised the population remains stable. This is because most of the eggs e.g. in sockeye salmon are eaten by predators, or young ones die from disease or starvation . Similarly many poppy seeds may be eaten by birds or not dispersed in the right place or no water or nutrition. Although enough is produced so that the population is stable

Competition: How does competition help in natural selection?

Organisms surviving the early stages of life compete for resources like plants for water, light, space and nutrients animals for food, water, territories and mates. The struggle for existence. This leads to survival of some who are successful competitors.( differential survival ) This is because they have features that help them gain the resources they need. Competition is most within the same species as they need the same resources. Individuals of different species also compete but it is not as fierce e.g. one feeds at night other feeds during the day.

Adaptation : How does it help natural selection?

The organisms that survive are the best adapted to their particular environment because of their inherited features and they grow rapidly, breed successfully to pass on their genes to their offsprings.

Evolution : How does it help natural selection?

If the environment does not change the naturally selected population does not change much. Extremely variant ones do not survive e.g. very long or short winged female sparrows are killed by stormy weather before they can breed. If environment changes some survive changed conditions because of the right features and compete and breed successfully. Natural selection brings about changes in species over time leading to evolution. The idea first proposed by …..?

Antibiotic Resistance :

Normal bacterialPopulation

Resistant because of mutation

Non resistant

Antibiotic taken for infection

Resistant bacteria grow due to mutation which enables them to produce an enzyme that break down the antibiotics and reproduce but non resistant ones stop growing or reproducing or killedAntibiotic

continued

All non resistant bacteria killed Selection has taken place for resistant ones

Artificial Selection and Genetic Engineering

Objectives:*Describe the role of artificial selection with examples in producing varieties of animals and plants with increased economic importance**Define the term genetic engineering***Describe how bacteria can be genetically engineered to produce human insulinStarter: What characteristics would be selectively breed for in farm animals?

Mark your homework Copy and fill in blanks with words provided.

Mutations can occur _________ when DNA is incorrectly copied during replication. Gene mutation may start in a single ________ of one cell. As the cells _________ to produce more cells, the number of cells carrying the new form increase. Mutations that occur in body cells can cause __________ cell division, resulting in cancer. Most mutations are ___________. However, they also play a part in how species ________. Changing by acquiring new forms of old genes is how living things have evolved by ________ ________.

evolve naturally natural harmful selection

nucleus divide uncontrollable

evolve

naturally

natural

harmful

selection

nucleus divide

uncontrollable

All correct A*, 1 wrong A, 2 wrongs B, 3 wrongs C , 4 wrongs D, 5 wrongs E, 6 wrongs F, 7 or more wrongs U

H/w due in on 1/11Answer either Core question:Describe the procedure a farmer would take to improve the milk yield of a herd of cows.orExtension question:List the stages that show how the insulin gene was removed from a human cell and grown in a bacterial cell.

Selective breeding or Artificial Selection• Process:

– Select wanted characteristics e.g. fast growth, high yield , disease resistance, docile nature, short stem(so less straw)

– Select individuals with characteristics– Cross breed– Select suitable offspring– Cross breed over many generations

• Advantages:– Improved agricultural yields

• Disadvantages:– Reduce gene pool leading; to reduction in variation

accumulation of harmful recessive characteristics due to inbreeding. e.g. lameness in dog due to underdeveloped hip joints

Why do these mice glow in the dark?It’s because they’ve had a jellyfish gene inserted into their DNA.

The gene codes for a fluorescent protein.

With the jellyfish gene in their cells, the mice make the protein and glow too.

So Genetic engineering is a process by which a section of DNA(gene) from one organism is inserted into the DNA of another organism. This allows transfer of genes between unrelated species who can’t breed with each other hence can’t be achieved by artificial selection

This is an example of recombinant DNA technology, more commonly called genetic engineering

Genetic engineering of bacteria

Genetic engineering of plants