GeneticsGeneticsGenetics

What is Genetics ?

Genetics is the study of heredity and variation

Examples of genetic variation

1. Domesticated species

2. Human genetics

3. Natural Populations

History of Genetics

•Domestication of animals

•Cultivation of plants

Cultivated varieties

Animal Breeds

Human Genetic Variation

Variance

Which suspect matches the blood stain ?

Bloodstain

Ethical Issues

Boot GM out of animal feed

Cloning

Genetic JournalsGenetic Journals• American Journal of Medical

Genetics Clinical Genetics

• Developmental Genetics Human Molecular Genetics

• Genetics European J. of Human Genetics

• Genetics Selection Evolution Nature Genetics

• Genetika Fungal Genetics and Biology

• Genome Cancer Genetics and Cytogenetics

• Genomics American J. Human Genetics

• Hereditas Opthalmic Genetics

• Japanese Journal of Human Genetics Human Genetics

• Journal of Heredity Current Genetics

• Molecular Biology and Evolution Animal Genetics

• Molecular Ecology Brazilian J. Genetics

• Molecular and General Genetics Biochemical Genetics

• Theoretical and Applied Genetics J. of Medical Genetics

• Trends in Genetics

Basic Concepts of Genetics

Nucleus - contains genetic material

DNA - genetic material

4 bases (nucleotides G, C, A, T)

Gene - functional unit of heredity

sequence of 4 nucleotides

Chromosome -linear DNA molecule

Basic Concepts of Genetics

Cell/nuclear division

•Mitosis (somatic tissue):

identical cells

•Meiosis (germ tissue):

gametes

Basic Concepts of Genetics

• Mendelian Genetics(transmission genetics)

• Molecular Genetics (hereditary material)

Historical Notes

1865 Gregor Mendel

- controlled genetic

experiments (garden peas)

- statistical regularity

- theory of inheritance

Understanding Genetics

• Relationship between:

GENOTYPE

ENVIRONMENT

PHENOTYPE

set of genes morphology

inherited physiology

behaviour

Mendelian Genetics

Requirements:

1. Attributes of the phenotype that

vary among individuals

2. Phenotypic variation caused by

genetic differences

Genotype and Phenotype

• The genotype is our actual genes. We cannot see our genes.

• The phenotype is the physical expression of those genes.

• Genes - cannot be observed directly

• Phenotypes - observed directly

** inheritance of phenotypes used to infer the inheritance of genes

Mendelian Genetics

Mendel’s ExperimentsSeven Pea varieties “True Breeding Lines”

Character “traits” Phenotypes

1. seed shape round, wrinkled

2. seed colour yellow, green

3. flowers (pods) axial, terminal

4. pods full, constricted

5. pods yellow, green

6. flowers violet, white

7. stem tall, dwarf

Fertilization

Gametes carry the genetic information about

an organism.

The male gamete produce Sperm.

The female gametes produce Eggs.

The process in which one gamete is united

with another is called Fertilization.

FertilizationMommy DaddyDaddy

BABYBABY

Self-Fertilization

• When an organism has both male and

female gametes, they are able to self-

fertilize.

Advantages

• easy to grow

• matures in a season

• self-fertilizing

• easy to cross-fertilize

Dominance

• Some characteristics overshadow others when crossed.

• This is referred to as a Dominant trait.

• The unseen trait is said to be Recessive.

• Dominant traits are represented on charts by a capital letter.

• Recessive traits are represented by a lower case letter

Pure Lines(Homozygous)

• When an organism is said to be of pure lines, it means their genotype is two identical alleles.

• TT is the pure line for a tall plant.

• tt is the pure line for a short plant.

Hybrids(Heterozygous)

• When parents of two different pure lines are crossed, the offspring are called hybrids.

• A hybrid’s genotype consists of two different alleles.

• The genotype Tt would be a tall plant hybrid.

Homozygous and Heterozygous

• When an organism has identical alleles, it is said to be homozygous.

• TT, and tt would both be homozygous

• When an organism has two different alleles, it is heterozygous.

• Tt is heterozygous.

Punnett Square

T T

T

T

TT

TT

TT

TT

Cross Pollination

Punnett Square of Cross Pollination

T t

T

T

TT

TT

Tt

Tt

MOM

DAD

Punnett SquarePunnett Square

(Monohybrid Cross)(Monohybrid Cross)

T t

T

t

TT

Tt

Tt

tt

MOM

DAD

Punnett SquarePunnett Square

T t

t

t

Tt

Tt

tt

tt

MOM

DAD

Punnett SquarePunnett Square

t t

t

t

tt

tt

tt

tt

MOM

DAD

Mendel’s Experimental Approach

Suitable experimental organism

• examine few traits in each experiment

• accurate quantitative records

• analyzed data formulated hypotheses

Genetic Analysis (pea shape)

Hypothesis to explain results

1. Hereditary determinants (genes)

2. Each adult plant has a gene pair

F1 plants: one gene dominant phenotype

one gene recessive phenotype

Hypothesis (continued)

3. Members of a gene pair segregate equally

into the gametes

4. Each gamete has only one member of a gene pair

5. Gametes combine at random to form zygote

Hypothesis

Self Fertilization

Test of Equal Segregation Hypothesis

Three parts:

1. Hereditary characteristics are determined by distinct units or factors.

2. For each characteristic, an individual carries two factors, one inherited from each parent.

3. The two factors of each pair segregate from each other and end up in separate gametes.

Principle of Segregation

If a plant is short, what is its genotype?

• It must be homozygous recessive, tt.

If a plant is tall, what is its genotype?

• It could be homozygous dominant, or heterozygous. TT, or Tt.

• To determine which genotype it is we use a test cross.

Test Cross

T t

t

t

Tt

Tt

tt

tt

Heterozygous

Known homozygous

recessive

1/2Tall

1/2Short

Test Cross

T T

t

t

Tt

Tt

Tt

Tt

Homozygous

Known homozygous

recessive

AllTall

N0Short

Genetic Terminology

Genes: hereditary elements • Alleles: forms of a gene: A a

• Heterozygote: Aa

• Homozygotes: AA aa

• Genotype: Genetic makeup

• Phenotype: What we actually see

• Dominance AA, Aa same phenotype

Summary

Experimental:

1. Two pure breeding lines

2. Cross --------> F1 hybrid

3. Self F1 ------> F2

Summary

Results:

1. F1 one phenotype

2. F2 3:1 ratio of 2 phenotypes

Summary

Inference:

1. Single major gene

2. dominant phenotype

3. equal segregation

4. existence of genes inferred