1 What phenotypic ratio is expected when a double heterozygo

1. What phenotypic ratio is expected when a double heterozygote in the cis configuration is crossed with a double heterozygote in the trans configuration and the gene are tightly linked. Please show work.

Solution

As, it is mentioned that the genes are tightly linked, there is no chance of crossing over between the genes.Let us represent the cis-double heterozygote as AB//ab and the trans double heterozygote as Ab//aB. So, after the cross, the genotypes will be AB//Ab, AB//aB, aB//Ab and ab//aB. So, 75% of the progeny will show the dominant phenotype and 25% of the progeny will show the recessive phenotype for one gene.