In guinea pigs, two genes that affect coat color and coat texture are on the sam
ID: 161749 • Letter: I
Question
In guinea pigs, two genes that affect coat color and coat texture are on the same autosomal chromosome. Brown (BL) is dominant to blonde (bl), and smooth (R) is dominant to rough (r). You set up crosses in which one parent is heterozygous and the other is homozygous for the recessive alleles and get the following results: 36 brown, smooth 29 blondes, rough 18 brown, rough 17 blondes, smooth Determine the orientation of dominant vs. recessive alleles on the heterozygous parent's chromosomes. Calculate the distance between the coat color and coat texture genes and draw the genetic map.Explanation / Answer
a) The heterozygous parent has B, b and R, r aleles. SO the orientation of allels on chromosome is: BR//br. Since they are heterozygotes, they carry both dominant and recessive allele of both the genes on chromosomes. // indicates the homologous chromosomes.
b) When no recombinatioin takes place between these two alleles, then all parental types are formed like BR//br and br//br. (36 and 29 in the given table). If recombination occurs between B and R genes then, Bb//rr and bb//Rr (18 and 17 in table) are produced.
So distance between the genes = single cross over events between B and R / total progeny
= 18+17 / 100
= 0.35 mU.