Genetics and Heredity

Our Hero Gregor Mendel

Mendle’s Pea Experiment

Height-Tall vs Short Seed Shape-Round vs Wrinkled Seed Color-Yellow vs green Flower Color- Purple vs White Flower Position- Axial vs Terminal Pod shape- Inflated vs Constricted Pod Color- Green vs yellow

Anatomy of a Flower

Making A Punnett Square

GametesTT X tt

Male Female

Completed SquareTT

MaleX tt

Female

T

T

t t

Terminology

Homozygous-two of the same alleles for a given trait

Dominant

Recessive Heterozygous-each cell of an organism contains two different

alleles for a given trait

Example:

Tt X Tt

More Terminology Genotypic Ratio- the combination of alleles for a given trait (gene

combination) Phenotypic Ratio- a ratio of what the offspring look like

Test of SegregationTest cross

Rr X rr RR X rr

Mendle’s Conclusions

Principle of Dominance- one form of a hereditary trait (dominant), dominates or prevents the expression of the recessive trait.

Principle of Segregation- during gamete formation the pair of genes responsible for each trait separates so that each gamete receives only one gene for each trait.

Incomplete Dominance

Dihybrid Cross

THE PRINCIPLE OF INDEPENDENT ASSORTMENT

GENES FOR DIFFERENT TRAITS SEGREGATE INDEPENDENTLY DURING GAMETE FORMATION

Multiple Alleles-Codominance

Blood type A

Blood type B

Blood type AB

Blood type O

IAIA IA iO

IBIB IBiO

IAIB

iOiO

G e n o t y p e s

Mendel’s Work Revisited

In the early 1900’s Walter Sutton observed meiosis in grasshoppers. He concluded that chromosomes do indeed behave like Mendel had thought. It also started the idea that genes are on the chromosomes.

Thomas Hunt Morgan

His work was on fruit flies Experimented with the sex chromosomes X and Y chromosomes differ between the

sexes so they are called sex chromosomes

The other chromosomes are called autosomes

Sex DeterminationMale Female

Sex-Linked Inheritance

XRXR XrYRed Eyed Female White Eyed Male

Can We Get A White Eyed Female?XRXr XrY

Red Eyed Female White Eyed Male