Mendelian Genetics

Page
3

Slide 25

Did the observed ratio match the theoretical ratio?

The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled

Mendel’s observed ratio was 2.96:1

The discrepancy is due to statistical error

The larger the sample the more nearly the results approximate to the theoretical ratio

Slide 26

Generation “Gap”

Parental P1 Generation = the parental generation in a breeding experiment.

F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation)

From breeding individuals from the P1 generation

F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation)

From breeding individuals from the F1 generation

Slide 27

Following the Generations

Cross 2 Pure Plants TT x tt

Results in all Hybrids Tt

Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt

Slide 28

Monohybrid Crosses

Slide 29

Trait: Seed Shape

Alleles: R – Round r – Wrinkled

Cross: Round seeds x Wrinkled seeds

RR x rr

P1 Monohybrid Cross

R

R

r

r

Rr

Rr

Rr

Rr

Genotype: Rr

Phenotype: Round

Genotypic Ratio: All alike

Phenotypic Ratio: All alike

Slide 30

P1 Monohybrid Cross Review

Homozygous dominant x Homozygous recessive

Offspring all Heterozygous (hybrids)

Offspring called F1 generation

Genotypic & Phenotypic ratio is ALL ALIKE

Slide 31

Trait: Seed Shape

Alleles: R – Round r – Wrinkled

Cross: Round seeds x Round seeds

Rr x Rr

F1 Monohybrid Cross

R

r

r

R

RR

rr

Rr

Rr

Genotype: RR, Rr, rr

Phenotype: Round & wrinkled

G.Ratio: 1:2:1

P.Ratio: 3:1

Slide 32

F1 Monohybrid Cross Review

Heterozygous x heterozygous

Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr

Offspring called F2 generation

Genotypic ratio is 1:2:1

Phenotypic Ratio is 3:1

Slide 33

What Do the Peas Look Like?

Slide 34