Gregor Mendel and Genetics

The Work of Mendel• Genetics = scientific study of heredity• Heredity = characteristics that are

passed on to the next generation• Gregor Mendel (1800’s)

– Grew up as a peasant farmer– Austrian Monk, high school science

teacher, in charge of monastery gardens.– Used garden peas for experiments

Mendel was successful because: peas are self-pollinating (inherit all

characteristics from plant that bore them)

Had true breeding stock = basis for experiment

Can cross pollinate (uses 2 parents) Controlled experiment Kept careful records !

Traits studied

Chose several traits that were true-breeding and had two distinct forms

Seed shape: round vs wrinkled

Seed color: Yellow vs green Gray seed coat vs white seed coat Smooth pod shape vs constricted pod Pod color = green vs yellow Flower position = axial vs terminal Height = tall vs short

Mendel’s ExperimentP = parental generation, original pair, true

breeding, tall x shortCross pollination:F1 generation = first filial generation

results in hybrids (from parents with contrasting traits)

results: all tallSelf pollination:F2 generation = second filial generation

¾ tall, ¼ short

MENDEL’S CONCLUSION:

“Factors” governed the expression of each trait (factors now called ?)

Each trait = controlled by a pair of genes, two factors

(ex. 1 for tall, 1 for short)

Allele = different forms of a trait, one of the gene pair

Principle of Dominance

• 1 of the genes in a pair may prevent the other gene from being expressed.

• Dominant gene = one which masks the other in a pair

• Recessive gene = one which is hidden (may reappear in F2)

• Dominant allele = expressed by a capital letter (ex. Y = yellow)

• Recessive allele = lower case (ex. y = green)

Principle of Segregation

• Members of each pair of genes separate during gamete formation **********