Answer to Question #108563 in Genetics for J

Question

A fruit fly that heterozygous for gray body with vestigial wings (b+ b+ vg+ vg) is mated with one that is true-breeding for black body with normal wings (b b+ vg vg). The genes for body color and wing structure are on the same chromosome. From previous research you know that they are 19 map units apart.

What are the possible offspring that could come from this cross? Label the offspring parental or recombinant.



What is the phenotypic ratio you would expect if the genes were on separate chromosomes?



What is the phenotypic ratio you would expect knowing that they are only 19 units apart

Answer 1

Parental genotypes are:

• b⁺ b⁺ vg⁺ vg - gray body and vestigal wings
• b b⁺ vg vg - black body and normal wings

The possible offspring are:

• b⁺ b vg⁺ vg - black body and vestigal wings (recombinant)
• b⁺ b vg vg - black body and normal wings (parental)
• b⁺ b⁺ vg⁺ vg - gray body and vestigal vings (parental)
• b⁺ b⁺ vg vg - gray body and normal wings (recombinant)

The phenotypic ratio if genes were on separate chromosomes:

• 0.25 or 1/4: b⁺ b vg⁺ vg
• 0.25 or 1/4: b⁺ b vg vg
• 0.25 or 1/4: b⁺ b⁺ vg⁺ vg
• 0.25 or 1/4: b⁺ b⁺ vg vg

The recombination of parental chromosomes would not change the phenotypic ratio of the offspring as the recombination would result in the formation of the same gametes. For example, a fruit fly with genotype b⁺ b⁺ vg⁺ vg produces gametes b⁺vg⁺ and b⁺vg with and without recombination.