Beyond Mendelian Genetics Incomplete Dominance Mendel was lucky

Beyond Mendelian Genetics: Incomplete Dominance Mendel was lucky! Traits he chose in the pea plant showed up very clearly… One allele was dominant over another, so phenotypes were easy to recognize. But sometimes phenotypes are not very obvious…

Incomplete Dominance Snapdragon flowers come in many colors. If you cross a red snapdragon (RR) with a white snapdragon (rr) You get PINK flowers (Rr)! RR rr Genes show incomplete dominance when the heterozygous phenotype is intermediate (a blend of the two Rr alleles).

Incomplete dominance When F 1 generation (all pink flowers) is self pollinated, the F 2 generation is 1: 2: 1 red, pink, white Incomplete Dominance R r R R Rr Rr rr

Incomplete dominance What happens if you cross a pink with a white? A pink with a red?

Codominance • Two alleles are expressed (multiple alleles) in heterozygous individuals. • Example: blood type • • 1. 2. 3. 4. Phenotye type A B AB O = = Genotype(s) IAIA or IAi IBIB or IBi I AI B ii copyright cmassengale 5

Codominance Problem • Example: • homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IA i IB I AI B I Bi copyright cmassengale 1/2 = IAIB 1/2 = IBi 6

Another Codominance Problem • Example: male Type O (ii) x female type AB (IAIB) IA IB i I Ai I Bi copyright cmassengale 1/2 = IAi 1/2 = IBi 7

Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? • boy - type O (ii) • girl - type AB (IAIB) copyright cmassengale 8

Codominance • Answer: IB i IA i I AI B I Ai ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale 9