Independent assortment versus genetic linkage

(a) For this dihybrid, four genetically different gametes are expected at 25% each when the genes assort independently. (b) When genes are linked, parental gametes are significantly more frequent than expected by chance, and their individual and combined frequencies are much greater than nonparental gametes(a) For this dihybrid, four genetically different gametes are expected at 25% each when the genes assort independently. (b) When genes are linked, parental gametes are significantly more frequent than expected by chance, and their individual and combined frequencies are much greater than nonparental gametes

(a) Independent assortment CentromereA B a b P as: an X _ .- a AABB aabb Gamete formation Gamete formation A l B a l .- ab “:6 '0‘ A . Gamete union Genesasson flu. c:- independentlY- a b AaBb l Gamete iormation Genotype Phenotype Frequency A B AB a b Parental ab - --3 =25% gametes(=50%) a a8 .- as: =25% A b Nonparental Ab 3:.- =25% gametes(=50%) \ Independent assortment predicts 25% of each gamete type, with parental and nonparental gametes each totaling 50%. (b) Genetic linkage D d E P d m Syntenic genes are m x a? close to one another. De E DDee (De/De) ddEE (dE/dE) Gamete formation Gamete formation l De l dE m De dE Gamete union m . Crossover may occur F1 m between homologs. d E DdEe (De/dE) | Gamete formation l Genotype Phenotype Frequency De >> 25% Parental dE >> 25% gametes (>>50%) DE << 25% Nonparental de << 25% gametes (<<50%) Parental gametes are significantly more frequent (>>) and nonparental gametes significantly less frequent (<<) than predicted by independent assortment.