Genetics Special Cases Incomplete Dominance One allele cannot

Genetics : Special Cases

Incomplete Dominance One allele cannot completely dominate the other. A new trait is produced

Incomplete Dominance

Incomplete Dominance �Example: snapdragons (flower) red (R) x white flower (r) RR = red flower R rr = white flower r Rr = pink flower r R

Incomplete Dominance R R r Rr Rr Genotypes: Rr Genotypic Ratio: all alike Phenotypes: Pink Phenotypic Ratio: all alike

Incomplete Dominance �Example: snapdragons (flower) red (R) x white flower (r) RR = red flower rr = white flower Rr = pink flower R R r r

Incomplete Dominance R r RR Rr Rr rr Genotypes: RR, Rr, rr Genotypic Ratio: 1: 2: 1 Phenotypes: Red : Pink : White Phenotypic Ratio: 1: 2: 1

Incomplete Dominance In snapdragons, red (RR) flowers and white flowers (WW) are incompletely dominant and when crossed produce a new phenotype: pink flowers (RW). Cross a red (RR) flower with a pink flower (RW) 1. What is the probability of having white offspring? 2. What is the probability of having Pink offspring? 3. What is the probability of having Red offspring? 4. What is the probability of having Heterozygous offspring? 5. What is the probability of having Homozygous offspring?

Codominance �When both dominant alleles show in the offspring

Sex – Linked Traits �Traits (genes) genes located on the sex chromosomes XX genotype for females XY genotype for males �Sex – linked traits are usually carried on the X chromosome

Sex – Linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color XX chromosome - female Xy chromosome - male

Sex – Linked Trait Problem �Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r Remember: the Y chromosome in males XR y does not carry this trait. RR = red eyed Rr = red eyed rr = white eyed Xy = male XX = female Xr Xr

Sex – Linked Trait XR Xr y Xr XR Xr Xr y 50% red eyed female 50% white eyed male

Multiple Allele Traits �Traits having more than one allele that can be found in a population �Example: Human Blood Types has 3 alleles rather than 2 There are four distinctly different Blood types

Multiple Allele Problem �Example: homozygous female Type B (IBIB) x heterozygous male Type A (IAi) IB IB IA I AI B i I Bi Genotypes= IAIB, IBi Genotypic Ratio=2: 2 Phenotypes=AB, B Phenotypic Ratio=2: 2

Multiple Allele Problem male Type O (ii) ii x female type AB (IAIB) Example: IA IB i I Ai I Bi 1/2 = IAi 1/2 = IBi

Multiple Allele �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) X girl - type AB (IAIB)

Multiple Allelle �Answer: IA IB i i I AI B ii Parents: genotypes = IAi and IBi phenotypes = A and B

Female Carriers

Polygenic Traits �Traits that are controlled by several genes at the same time �Example: Human Eye Color Alleles : A, a, B, b, C, c Dark Brown = AABBCC Green = Aa. Bb. Cc Light Blue = aabbcc