Question

Baldness is a dominant trait that is influenced by an individual's sex. a man will become bald if he has the genotype bb or bb. a man who is bb will not become bald. a woman will have thinning hair, but not become totally bald, if she is bb. a woman will not become bald, or have thinning hair, if she is bb or bb.

what will be the outcome if a woman who is xxbb produces a child with a man who is xybb?
a
there is a 75% chance that the child will be a female who will have thinning hair.

b
there is a 50% chance that the child will be a male who will become bald.

c
there is a 12.5% chance that the child will be a male who will not become bald.

d
there is a 25% chance that the child will be a female who will not have thinning hair.

Answer 1

The outcome of a cross between a woman who is homozygous for the baldness trait but phenotypically normal (incorrectly noted as XXbb but should be XBXb) and a man who is heterozygous for the baldness trait and bald (XB Y), is that there is a 25% chance that the child will be a female who will not have thinning hair.

Step-by-step explanation:

If a woman who is XXbb (homozygous for the baldness trait but phenotypically normal due to being female) has a child with a man who is XYBb (heterozygous for the baldness trait and bald), then we have to consider all possible combinations of their alleles and the sex of the offspring. Because a mother can only pass on an X chromosome and the father can pass on either an X or a Y, the sex of the baby is determined by the father with a 50% chance for each sex. When considering the baldness trait, a male who inherits the recessive allele will be bald (bb), and a female with at least one B allele will not show baldness (Bb or BB).

However, the question as presented contains a typo in the genotype representation regarding the male alleles which should be XB and Y for a male to express baldness dominantly when only one allele is needed. If we correct this and work with a typical dominant and recessive representation (B for the bald allele and b for the non-bald allele), we can analyze the cross with a Punnett square.

For correct prediction, we use B and b for the baldness trait, where B is dominant. The genotypes are:

Woman: XBXb (although mentioned as XXbb, treated as a typo)

Man: XBY

Offspring possibilities:

50% females:

50% males:

Therefore, the correct answer would be: D - there is a 25% chance that the child will be a female who will not have thinning hair.

Answer 2

C. There is a 12.5% chance that the child will be a male who will not become bald. This is because the man is xybb, which means he has one copy of the baldness gene (B) and one copy of the non-baldness gene (b). The woman is xxbb, which means she has two copies of the non-baldness gene. Since the man has one copy of the baldness gene, there is a 50% chance that any male offspring will inherit the baldness gene, and a 50% chance that any female offspring will inherit the non-baldness gene. Therefore, the chances of the male offspring not inheriting the baldness gene (and not becoming bald) is 50% * 50% = 12.5%.