Question

In Nitrovian flyti, with biological systems identical to those of earth fruit flies, there is a phenotype, Tofutti, in which the flyti are strictly vegetarian. If a true-breeding female (non-vegetarian) is mated with a vegetarian male, they produce 1000 F1 offspring in the following counts: 523 non-vegetarian female flyti; 477 non-vegetarian male flyti. In a reciprocal cross, the numbers of F1 offspring produced are: 502 non-vegetarian female flyti; 498 vegetarian male flyti. The most likely explanation for these results is:

A. The gene coding for Tofutti is X-linked dominant.
B. The gene coding for Tofutti is autosomal dominant and homozygous lethal.
C. The gene coding for Tofutti is X-linked recessive.
D. There is insufficient information to answer this question.
E. The gene coding for Tofutti is autosomal recessive and homozygous lethal.

Answer 1

C. The gene coding for Tofutti is X-linked recessive.

Step-by-step explanation:

In first cross :

non vegetarian female X vegetarian male = The entire progeny is non vegetarian.

In second cross :

vegetarian female X non vegetarian male = all females are non vegetarian and all males are vegetarian

If the gene for this trait is X-linked recessive then the above results can be explained as follows :

First cross : XTXT X XtY :

XT XT

Xt XTXt XTXt

Y XTY XTY

All males have dominant XT allele so they all will be non vegetarian. All females are heterozygous so they will also be non vegetarian.

Second cross : XtXt X XTY :

Xt Xt

XT XTXt XTXt

Y XtY XtY

All males have recessive Xt allele so they all will be vegetarian. All females have one dominant XT allele so they all will be non vegetarian.