Question

Question text

In drosophila (fruit flies):

• The yellow gene is on the X-chromosome, the gene product plays a role in body colour. Wild type flies are a light brown/tan in colour, homozygote yellow mutants have a more yellow shaded body colour. We'll use y⁺ to represent the wild type allele, and y to represent the mutant allele. y⁺ is dominant to y.
• The vestigial gene is on chromosome 2. Homozygote vestigial mutants have very short wings, and cannot fly. We'll use vg⁺ to represent the wild type allele, and vg to represent the mutant allele. vg⁺ is dominant to vg.
• The scarlet gene is on chromosome 3. Homozygote scarlet mutants have bright red eyes, while wild type flies have darker brownish-red eyes. We'll use st⁺ to represent the wild type allele, and st to represent the mutant allele. st⁺ is dominant to st.
• Males are usually XY, and females are usually XX

You cross two flies. The female has the mutant phenotype for all three traits (homozygote recessive for all three genes). The male has the wild type phenotype for all three traits, and you know he is heterozygote for scarlet and vestigial.  

Which offspring phenotype will you see the least of? Explain your answer.

• Females that have scarlet eyes and yellow bodies, if wing size doesn't matter (i.e., can have either very short wings or normal wings).
• Males that have normal wings and yellow bodies, if eye colour doesn't matter (i.e., can have either very short wings or normal wings).
• Males with scarlet eyes and wild type/normal looking bodies, if wing size doesn't matter (i.e., can have either very short wings or normal wings).

Answer 1

Cross has been made between female with all three traits as mutant and male has all wild type phenotype but heterozygote for scarlet and vestigial

yyvgvgstst x yy+vgvg+stst+

yvgst,

so, the offspring obtained will be

	yvgst	yvg+st	yvg+st+	y+vgst	y+vg+st	y+vgst+	yvg+st+	y+vg+st+
yvgst	yyvgvgstst	yyvgvg+stst	yyvgvg+stst+	yy+vgvgstst	yy+vgvg+stst	yy+vgvg+stst+	yyvgvg+stst+	yy+vgvg+stst+
yvgst	yyvgvgstst	yyvgvg+stst	yyvgvg+stst+	yy+vgvgstst	yy+vgvg+stst	yy+vgvg+stst+	yyvgvg+stst+	yy+vgvg+stst+

Phenotypically offspring with all mutant type allele i.e., only two. while all others will be higher in no.