The Living EnvironmentThe Living Environment

The study of organisms and The study of organisms and their interactions with the their interactions with the

environment.environment.

TopicsTopics

• Unit 1: EcologyUnit 1: Ecology

• Unit 2: The CellUnit 2: The Cell

• Unit 3: GeneticsUnit 3: Genetics

• Unit 4: History of Biological DiversityUnit 4: History of Biological Diversity

• Unit 5: The Human BodyUnit 5: The Human Body

GENETICS

The science of heredity and the study of how traits are passed on

from generation to generation.

Mendelian Genetics: How Genetics Began• Commonly referred to as the

“father of modern genetics” Gregor Mendel, born in 1822 in what is now the Czech Republic, published the first known findings of heredity in 1866.

• His primary findings were based on the study of pea plants during his 14 year tenure as an Austrian monk in charge of the monastery garden.

Mendelian Genetics• While tending his plants,

Mendel was intrigued by the pea plants because he noticed that some were tall while others were short; some had white flowers and some had purple flowers; some had green peas and others had yellow peas.

• Mendel was determined to try to figure out what determined these different traits as well as others and began experimenting.

Plant Sexual Reproduction• Pollen, produced by the

anther, is transferred to the stigma, travels down the style into the ovary, and fertilizes the ovule producing a seed.

• Self-pollination occurs when pollen is transferred to the stigma of the same plant.

• Cross-pollination occurs when pollen is transferred to the stigma of another plant.

Mendelian Genetics• Mendel began cross

pollinating plants with similar traits and plants with varying traits and recording the outcomes of these crosses in a journal.

• From these various crosses performed over many years, Mendel concluded that traits are passed on from one generation to the next and wrote three laws regarding his findings.

Mendelian Genetics• The Law of Dominance states

that certain traits exhibit dominance over others which are said to be recessive.

• In other words, if two different alleles of the same trait are combined to form offspring, all of the offspring will exhibit the dominant allele.

• The only way for the offspring to express the recessive allele would be for both inherited alleles to be the recessive form of the trait.

Mendelian Genetics• The Law of Segregation, later

proven by the discovery of the process of meiosis, states that each gamete, produced by each parent, receives only one allele of each trait; thus the alleles of each trait are segregated amongst the gametes.

• In other words, each sperm and egg produced only carries one allele for each trait resulting in offspring who receive one allele of each trait from each parent.

Review of Meiosis• Recall that meiosis results

in four daughter cells each containing half the number of chromosomes as the original cell and half the alleles of each gene.

• These daughter cells are also genetically different from the parent cell and from each other due to cross-over that occurs during prophase of meiosis I.

Mendelian Genetics• The Law of Independent

Assortment states that traits are inherited independently of each other.

• For example, with Mendel’s pea plants, the trait for plant height is inherited separately from the trait for pea color or flower color.

• This law does not apply to all traits in all organisms as some traits are genetically linked and are inherited together.

Probability and Punnett Squares• A genotype is a pair of

letters representing a particular genetic makeup, or type of genes. These letters are chosen based on the dominant allele.

• A phenotype is the physical characteristic exhibited by the organism as a result of its genotype.

• An organism’s phenotype is dependant on its genotype.

Probability and Punnett Squares• A homozygous pair of alleles is

represented by any two of the same letters, either both capital or both lowercase. This is known as a purebred trait, where both alleles are identical.

• It is possible for a homozygous trait to be dominant or recessive.

• A heterozygous pair of alleles is represented by two different letters, one capital and one lowercase. This is known as a hybrid trait and will always exhibit the dominant phenotype.

Probability and Punnett Squares

• In the early 1900’s Dr. Reginald Punnett developed the Punnett Square to predict the possible offspring of a cross between two known genotypes.

• Mendel’s journals show that even he was able to produce the ratios of offspring that we can now easily calculate using Punnett Squares.

Probability and Punnett Squares

• A monohybrid cross is a cross involving hybrids of a single trait.

• A monohybrid cross of the F1 generation will always result in 75% of the offspring exhibiting the dominant trait.

• A monohybrid cross results in a genotypic ratio of 1:2:1 and a phenotypic ratio of 3:1.

Probability and Punnett Squares• A dihybrid cross is a cross involving hybrids of two

different traits at the same time using a single Punnett Square.

• A dihybrid cross results in a genotype and phenotypic ratio of 9:3:3:1.

• Dihybrid crosses can be used to prove Mendel’s Law of Independent Assortment.

Incomplete Dominance

• Cases in which one allele is not completely dominant over another are called incomplete dominance.

• These traits are sometimes referred to as “blending” traits.

• Examples include pink carnations and palomino horses.

Examples of Incomplete Dominance

+ =

Codominance

• Codominance occurs when both alleles (from each parent) contribute to the phenotype of the offspring because neither is dominant.

• Codominance results in a heterozygous (hybrid) organism such as a roan cow which has both red and white hairs.

Polygenic Traits• Traits controlled by two or more genes are

called polygenic traits.• Polygenic traits often result in a wide range of

phenotypes such as the range of eye colors or the range of skin tones in humans.

The Discovery of DNA• Although Mendel’s journals were

discovered around the turn of the 20th century, scientists lacked the technology to perform genetic research in any greater detail than Mendel himself until about 1940.

• In 1944, Oswald Avery and his team determined that genes were composed of biochemical molecules called DeoxyriboNucleicAcid (DNA).

DNA as a Double Helix• In 1951, Linus Pauling and

Robert Corey determined that proteins like those found in the DNA molecule were a helical type of structure.

• In 1952, Rosalind Franklin using a technique called X-Ray diffraction took a “picture” of the DNA molecule.

• In 1953, James Watson and Francis Crick developed the double-helix model of the structure of DNA.

DNA – The Double-Helix• DNA, sometimes referred

to as a twisted ladder or spiral staircase, is a very long chain molecule, consisting of sub-units called nucleotides.

• Each nucleotide is made up of three basic structures:A sugar called

deoxyriboseA phosphate groupA nitrogenous base

DNA Structure• The backbone of the DNA

structure, or side rails, are formed by the sugar-phosphate groups of each nucleotide.

• Connecting the two rails of the DNA structure are four types of nitrogenous bases:Thymine (T)Adenine (A)Cytosine (C)Guanine (G)

DNA Structure• The side rails of the twisted

ladder are attached by the pairing of the nitrogenous bases extending from each side of the DNA molecule, creating the rungs of the ladder.

• Adenine always pairs with Thymine, while Guanine always pairs with Cytosine, thus creating the base pairs:

A – TG – C

DNA Structure

Chromosome Structure• Chromosomes consist of

tightly packed coils of DNA called chromatin.

• Chromatin consists of a DNA molecule tightly wound around proteins called histones.

• DNA consists of nucleotides which code for individual genes.

• Chromosome Chromatin DNA Gene Largest Smallest

• Chromosome Chromatin DNA Nucleotide

DNA Replication• During DNA replication, the DNA molecule separates

into two strands, then produces two new complimentary strands following the rules of base pairing.

• Each strand of the double-helix serves as a template for the new strand.

DNA Replication• DNA replication is carried out by a series of enzymes.• These enzymes “unzip” the DNA molecule

by breaking the bonds of the base pairs, then synthesize a complimentary strand of DNA for each of the original strands.

DNA Replication

The Structure of RNA• RNA, like DNA, consists

of a long chain of nucleotides, each made up of a sugar, phosphate group, and a nitrogenous base.

• RNA differs from DNA in three main ways:The sugar is ribose.RNA is single stranded.RNA contains Uracil (U)

in place of Thymine.

Function of RNA in Cells• The primary function of RNA in cells is protein

synthesis.• The assembly of amino acids into proteins is

controlled by RNA.• The three main types of RNA are:

mRNA (messenger) rRNA (ribosomal) tRNA (transfer)

Protein Synthesis• RNA is produced within a

cell from a strand of DNA through a process called transcription.

• mRNA is transcribed in the nucleus, enters the cytoplasm, and attaches to a ribosome.

• Next, translation of the mRNA strand occurs with assistance from tRNA within the ribosome, synthesizing proteins from amino acids.

Protein Synthesis• Proteins are made by

joining amino acids into long chains called polypeptides.

• Each polypeptide consists of a combination of any or all of the 20 different amino acids.

• The properties of these proteins are determined by the order in which the amino acids are joined to form the polypeptides.

The Genetic Code• The “language” of mRNA

instructions is called the genetic code.

• This code is written in a language that has only four letters, AUCG.

• The code is read three letters at a time so that each word of the coded message is three bases long.

• Each three letter word is known as a codon.

The Genetic Code

• A codon consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide.

• There are 64 possible three-base codons.

• Some amino acids can be specified by more than one codon.

Amino Acids

The Roles of RNA and DNA• DNA acts as the “master

plan” and is stored safely within the nucleus of the cells of an organism.

• DNA controls every action of a cell and essentially every characteristic of an organism by producing “blueprints” in the form of RNA which will translate into proteins that control cellular functions and characteristics.

Genetic Mutations• Mutations are changes in

the DNA sequence that affect genetic information.

• Gene mutations result from changes in a single gene.

• Chromosomal mutations involve changes in whole chromosomes.

• Mutations can be beneficial to an organism, deleterious to an organism, or have no effect at all.

Gene Mutations• Mutations that affect one nucleotide are called point

mutations.• Some point mutations substitute one nucleotide for

another, resulting in a change in the translated amino acid in a protein.

Gene Mutations

• If a nucleotide is inserted or deleted, a frameshift mutation can occur.

• Frameshift mutations typically result in big changes in the translated amino acids of the protein, often altering the protein so it is unable to perform its normal functions.

Chromosomal Mutations• Chromosomal mutations

involve changes in the number or structure of chromosomes.

• These mutations can result in the deletion of genes from chromosomes, the inversion of genetic code, translocation, and duplication of genes on chromosomes.

Human Traits• A pedigree is a diagram used to show how a particular

genetic trait is passed down from generation to generation – a genetic family tree.

• Squares represent males and circles represent females. A horizontal line connecting a square and circle illustrates a parental generation. Siblings are always drawn with the oldest to the left, youngest to the right.

Pedigrees• Pedigrees can illustrate carriers of a genetic trait, as

well as those exhibiting the effects of the trait.• Fully shaded squares/circles represent individuals

who exhibit the trait. (Homozygous dom./rec.)• Half shaded squares/circles represent individuals who

carry the trait but who do not exhibit the effects of the trait. (Heterozygous)

Pedigree of the Royal Family

Human Heredity• A karyotype is a micrograph

of the pairs of homologous chromosomes, taken during mitosis.

• Human cells each contain 22 pairs of autosomes and one pair of sex chromosomes equaling a total of 23 pairs (or 46) total chromosomes.

• Females have identical sex chromosomes (XX) while males have two different sex chromosomes (XY).

Autosomal Recessive Disorders

Autosomal Dominant Disorders

Sex-linked Genes• Many genes are found on the X and Y chromosomes

and are therefore referred to as sex-linked genes.• More than 100 sex-linked disorders have been

mapped on the X chromosome.• Sex-linked disorders include:

ColorblindnessHemophiliaDuchenne Muscular

Dystrophy

Colorblind Test

Sex-linked Disorders

Chromosomal Disorders• A typical chromosomal disorder results from an error

during meiosis called non-disjunction; when chromosomes do not separate evenly resulting in trisomy, or three copies of a particular chromosome instead of the usual two copies.

• Non-disjunction typically leaves some gametes containing only one copy of a chromosome, known as monosomy.

Chromosomal Disorders

• Alterations of chromosome number are serious, often fatal disorders.

• Down Syndrome, or trisomy 21, occurs due to non-disjunction resulting in offspring with 47 chromosomes; an extra chromosome # 21.

Chromosomal Disorders• Non-disjunction in sex

chromosomes can lead to disorders such as Turners Syndrome (X) and Kleinfelter’s Syndrome (XXY).

• Individuals with either of these disorders are sterile and therefore cannot reproduce and pass on their genetic disorder.

Extra Genetic Material Disorders

Chromosomal Disorders

• Cri-du-chat is a genetic deletion disorder whereby a part of the #5 chromosome was deleted during DNA replication.

• Typical effects of this disorder include mental retardation, pinched facial characteristics, and a cat-like cry.

Genetic Deletion Disorders

Multifactorial Chromosome Abnormalities

DNA Analysis• Gel electrophoresis is a

technique used to separate DNA fragments.

• Separating DNA fragments is useful in mapping a DNA fingerprint in order to solve criminal investigations and to perform genomic evaluations.

Gel Electrophoresis• DNA is extracted from a

cell(s), then cut into segments using a restriction enzyme.

• The DNA segments are then separated using gel electrophoresis.

• The segments are injected into wells at one end of an agarose gel.

• Once electricity is applied across the gel, the segments of DNA will spread across the gel.

Gel Electrophoresis

Gel Electrophoresis• These segments can be viewed under UV light.• A special camera is then used to photograph the gel

for comparison purposes or for use in court.

DNA Fingerprinting

• Short segments will travel further down the gel while long segments will stay closer to the wells.

• DNA fingerprinting can be used to identify a suspect in a criminal investigation or determine the father of a child.

Human Genome Project

• The Human Genome Project began in 1990, headed up in the US by James Watson, and was completed in June 2000, after a collaborative effort by geneticists around the globe.

• The goal was to determine the sequence of base pairs for the entire human genome and map all 30,000 genes in a human DNA strand.

• 1. There are approx. 30,000 genes in human beings, the same range as in mice and twice that of roundworms. Understanding how these genes express themselves will provide clues to how diseases are caused.

• 2. All human races are 99.99 % alike, so racial differences are genetically insignificant. This could mean we all descended from the original mother who was from Africa.

• 3. Most genetic mutation occur in the male of the species. So men are agents of change. They are also more likely to be responsible for genetic disorders.

• 4. Genomics has led to advances in genetic archaeology and has improved our understanding of how we evolved as humans and diverged from apes 25 million years ago. It also tells how our body works, including the mystery behind how the sense of taste works.

Key Findings of the Project…

Genetic Engineering• Genetic engineering is the purposeful altering or

selection of certain traits in an organism.• Selective breeding is an indirect method of genetic

engineering.• Selective breeding is the purposeful mating of

organisms with particular traits in order to produce offspring that exhibit the desired trait(s).

Genetic Engineering• Hybridization is a method

of selective breeding whereby two parents, each exhibiting different desired traits are crossed to produce a more desirable product.

• Inbreeding is the continued breeding of individuals with the desired characteristics, typically between members of the same “family” or same group of offspring.

Genetic Engineering: Manipulating DNA• DNA can be cut and

pasted to form a “new” strand of DNA called recombinant DNA.

• Enzymes are used to cut and paste the strands of DNA.

• PCR is a technique used to build recombinant DNA.

• The recombinant DNA can then be inserted into an organism, thus altering their genetic code.

Genetic Engineering: Cell Transformation• During transformation,

a cell takes in DNA from outside the cell.

• This external piece of DNA becomes part of the cell’s DNA.

• Plasmids are small, circular DNA molecules commonly found in bacteria.

• Once reinserted into bacterial cells, those cells can be used to transform other cells.

Genetic Engineering: Cell Transformation• Bacteria cells containing the recombinant DNA

plasmid can be used to alter the DNA in plant or animal cells in order to alter that organism’s genetic code.

• This procedure might be performed to genetically engineer a plant to have better resistance to insects or a cow to produce more milk.

Genetic Engineering: Cell Transformation

Genetic Engineering: Transgenic Organisms

• Transgenic organisms are genetically engineered organisms, created by inserting a gene(s) from one organism into another.

• Genetically modified organisms are created to study various traits in different organisms as well as to produce more useful organisms such as livestock that produce more growth hormone.

Genetic Cloning

• Genetic cloning involves the artificial reproduction of an organism that will be genetically identical to its parent organism.

• The first organism reported as being successfully cloned was a sheep named ‘Dolly’, reportedly cloned in Scotland in 1996.

Genetic Cloning• Dolly was cloned by inserting the DNA from a somatic

cell of one sheep into the egg cell, whose nucleus had been removed, of another sheep; then electrically stimulating the egg and implanting the embryo into the uterus of the surrogate mother.

Genetic Cloning• It has long been theorized that extinct organisms

might be resurrected if we could collect the organisms’ DNA from fossilized remains.

• The recently discovered baby mammoth will soon undergo a cloning-like process in an attempt to resurrect this long extinct creature.

• However, an ethical question must first be answered…should it be done if we can manage to do it?

• Mammoth Resurrection