Question

In Drosophila melanogaster, vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color. Morgan crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. The F1 females were crossed to homozygous recessive males to produce testcross progeny. Morgan calculated the map distance to be 17 map units. Which of the following is correct about the testcross progeny? In Drosophila melanogaster, vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color. Morgan crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. The F1 females were crossed to homozygous recessive males to produce testcross progeny. Morgan calculated the map distance to be 17 map units. Which of the following is correct about the testcross progeny? gray-bodied, normal-winged flies PLUS black-bodied, vestigial-winged flies = 17% of the total black-bodied, normal-winged flies = 17% of the total black-bodied, vestigial-winged flies = 17% of the total black-bodied, normal-winged flies PLUS gray-bodied, vestigial-winged flies = 17% of the total

Answer 1

gray bodied, normal-winged flies plus black bodies, vestigial-winged flies = 17%.

Step-by-step explanation:

Answer 2

The correct answer is gray bodied, normal-winged flies plus black bodies, vestigial-winged flies = 17%.

In the given case, the genes are linked, thus, there is no independent assortment. B is gray body (dominant), b is black body (recessive), W is normal wings (dominant), and w is vestigial wings (recessive).

The parent generation would be: bbWW × BBww

After crossing the parent generation, the F₁ generation would be BbWw

Even so, during forming gametes for the F₂ generation, one basically cannot arrange or randomly assort the alleles. One has to take into consideration that the chromosomes are Bw and bW, thus, they will produce crossovers.

25% Bw-Bw, 50% Bw-bW, 25% bW-bW

As there is a crossover event, so one cannot get an F₂ who was BW (gray bodied and normal winged), or bw (black bodies and vestigial winged). Hence, the mentioned answer indicates or suggests towards all the order of instance or occurrence where a crossover event has occurred that associates back to the map units.