Question

genetics

Analyze the following fruit fly cross. In this cross there are two autosomal traits that are influenced by two distinct genes and the F2 generation came from crossing an F1 male with an F1 female. P: true breeding grey eyed; brown bodied males x true breeding red eyed; black bodied females F1: all offspring are red eyed; brown bodied F2: ? When the F1 flies are allowed to self cross, what percentage of F2 flies will have both brown bodies and red eyes if the genes are completely linked (round to the nearest percent)

Answer 1

Answer: 50% of the F2 progeny will have both brown bodies and red eyes.

Explanation: Let the allele for red eyes be ‘R’ therefore allele for grey eyes will be ‘r’

Let the allele for brown body be ‘B’ then the allele for black body will be ‘b’

P (parents) are true breeding grey eyed, brown bodied male, the genotype will be rrBB, the gamates produced by them will be rB

And true breeding, red eyed, black bodied female will have the genotype as RRbb, gamates produced will be Rb

The F1 generation will be having the genotype as RrBb

And the phenotype will be red eyed, brown bodied as mentioned

Now if the genes were not linked then the gamates produced would have been of four types RB, Rb, rB and rb

But since the genes are completely linked the genes for both the characters are inherited as a single unit hence the type of gamates produced will be

rB and Rb by F1 generation

Hence we will get following combinations of the offspring

gamates	rB	Rb
rB	rrBB grey eyed, brown bodied	RrBb Red eyed, brown bodied
Rb	RrBb Red eyed, brown bodied	RRbb Red eyed, black bodied

Hence the percentage of red eyed, brown bodied offspring will be 50%

Note: Red eye and brown body are considered as the dominant characters as they appear in the F1 generation not allowing the expression of grey eye and black body characters.

Since the traits mentioned are autosomal hence the genders of the offspring are not considered.