Question

In tigers, a recessive allele causes an absence of fur pigmentation (a white tiger) and a cross-eyed condition.

Part A
If two phenotypically normal tigers that are heterozygous at this locus are mated, what percentage of their offspring will be cross-eyed? Express your answer using the percent symbol and no spaces (for example, 10%).
Part B What percentage of cross-eyed tigers will be white? Express your answer using the percent symbol and no spaces (for example, 10%).

Answer 1

A) 25%

B) 100%

Step-by-step explanation:

This involves a single gene. Let's assume the gene is Z. The dominant allele (Z) produces a tiger with normal phenotype i.e. presence of fur pigmentation and no cross eye while the recessive allele (z) produces a tiger with no fur pigmentation (white) and cross-eye.

According to the question, a heterozygous tiger will have normal phenotype because the dominant allele (Z) is masking the expression of the recessive pair (z). Hence, in a cross between Zz and Zz (two heterozygous tigers), four possible offsprings will be produced, in which three(3) will be phenotypically normal (Zz) and one(1) will be phenotypically recessive (zz) i.e. possess cross-eye and white furs. Hence, the percentage of cross-eyed (recessive) tiger offsprings will be 1/4 × 100 = 25%. (See attached image)

For question B; The recessive allele for the gene induces both lack of fur pigmentation and cross-eyed phenotypes I.e. The two recessive phenotypes are caused by the same recessive alleles on the same locus. This means that a tiger that is cross-eyed must also be white-furred or lack fur pigmentation. Hence, the percentage of having a cross-eyed tiger that is white is 100%.