Question

1. In an insect species, number of abdominal segments is determined by alleles of one gene. The dominant E allele determines eight segments, while the recessive e allele results in seven segments. A second unlinked gene determines body color. The dominant B allele determines brown color, while the recessive b allele results in yellow color. A homozygous 8-segmented, yellow insect is crossed with a homozygous 7-segmented, brown insect. What proportion of the gametes made by the F₁s carry at least one recessive allele?

   7/16

   3/4

   1/4

   3/8

   1/2

Answer 1

Given allele for dominant trait of eight segments be “E” and the allele for recessive trait of seven segments be “e”

Also, allele for brown color body is “B” and “b” is the allele for yellow color body.

Genotype of homozygous 8-segmented, yellow insect – EEbb

Genotype of homozygous 7-segmented, brown insect – eeBB

Gamete for of homozygous 8-segmented, yellow insect – Eb, Eb, Eb, Eb

Gamete for of homozygous7-segmented, brown insect – eB, eB, eB, eB

The following offspring’s will be produced –

	Eb	Eb	Eb	Eb
eB	EeBb	EeBb	EeBb	EeBb
eB	EeBb	EeBb	EeBb	EeBb
eB	EeBb	EeBb	EeBb	EeBb
eB	EeBb	EeBb	EeBb	EeBb

Genotype of all offspring – EeBb

Phenotype of all offspring – 8-segmented, brown insect

Gamete of EeBb – EB, Eb, eB, eb

Out of four gametes 3 have recessive allele

Thus, the probability of having gametes with recessive allele = 3/4