Mendel’s 1 st Law - Segregation Each individual has two alleles (copies) of every gene. These alleles separate during sperm/egg cell formation Mendel’s 2 nd Law – Independent Assortment During gamete formation, different pairs of alleles segregate independently of each other

A a B b Potential gametes A B1/4 A b1/4 a B1/4 a b1/4

AB & abAb & aB

X X P F1 F2 100 aa bbAA BB Aa Bb AB Ab aB ab

X F1 F X P BB CCbb cc Bb Cc BCbCBcbc

Gametes All parental50% parental 50% recombinant

X F1 F BCbC bc BC RF = 10.7 % so 10.7 m.u.

DCO lead to underestimation of genetic map distances Solution is to use three point cross

A female Drosophila is heterozygous at three autosomal linked gene loci: e+ brown bodyeebony body h+hairless legshhairy legs c+straight wingsccurvy wings In order to map these genes, this heterozygote is crossed to a homozygous male recessive fly and the following phenotypes of progeny were obtained: e h c 356 e+ h+ c+347 e+ h c2 e h+ c+3 e h c+42 e h+ c19 e+ h+ c53 e+ h c Why didn’t we do the cross the other way round i.e. with a heterozygous male?(1) Which is the middle gene?(2) Calculate the map distances between the genes.(4) Is there any evidence of interference? (2)