Dr. Hatesdogs has been raising exotic fruit flies for decades. Recently, she dis

Question

Dr. Hatesdogs has been raising exotic fruit flies for decades. Recently, she discovered a strain of fruit flies that in the recessive condition have baby blue eyes that she designates as bb. She also has another strain of fruit flies that in the recessive condition have pink wings that are designated as pw. She is able to establish flies that are homozygous for both mutant traits. She mates these two strains with each other. Dr. Hatesdogs then takes phenotypically wild-type females from this cross and mates them with double recessive males. In the resulting testcross progeny, she observes 500 flies that are of the following make-up:

41 with baby blue eyes and pink wings 207 with baby blue eyes only
210 with pink wings only
42 with wild-type phenotype

the wild-type alleles for these two genes are b+ and pw+, the testcross of the F1 flies is (c) b+ pw/b pw+ × b pw/b pw .

Refer to the information above. What is the relationship with respect to location between the two genes, b and pw?

(a) They are far apart on the same chromosome and assorting independently. (b) They are linked and the map distance between them is 41.5 cM.
(c) They are on different chromosomes and assorting independently.
(d) They are linked and 16.6 cM apart.

(e) They are linked and 50.0 cM apart.

Explanation / Answer

Initially she had mated b+b+ / pw pw and bb / pw+pw+

F1 result will be b+ pw / b pw+ (All wild type)

Test cross is b+pw / b pw+ (wild type eyes and wings) crossed with b pw / b pw (baby blue eyes and pink wings)

b+b pw+pw (will have wild types eyes and wings) = parental type = 42

b+b pwpw (wild type eyes and pink wings) = recombinants

bb pw+pw (baby blue eyes and wild type wings)= recombinants

bb pwpw (baby blue eyes and pink wings) = parental type =41

So, recombinants are more than the parental types, So, genes are not linked

The one which is having baby blue eyes only (=207) is not having wild type wings. This means that the unlinked genes are on different chromosomes.

So, (c) They are on different chromosomes and assorting independently:- (is the correct option).

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