Question

A man who is a dwarf with achondroplasia and normal vision marries a color-blind woman of normal height. The man's father was six feet tall, and both the woman's parents were of average height. Dwarfism caused by achrondroplasia is autosomal dominant and red-green color blindness is X-linked recessive. How many of their daughters might be expected to be color-blind with achrondroplasia?

Answer 1

Answer:

None of their daughters will be color-blind with achrondroplasia, but half of their children would be expected to have only achrondroplasia

Explanation:

Achrondroplasia is autosomal dominant and the man's father was normal and unaffected (aa) thus we can assume that the man's mother had achrondroplasia (AA or Aa). We can then say the man is Aa, inheriting the dominant allele from his mother. The woman is also aa because she is normal height, thus if we cross Aa with aa, we get 2 x Aa and 2 x aa, therefore half their children will have achrondroplasia.

Because red-green color-blindness is X-linked recessive we the know the woman is XᵇXᵇ because she is an affected female and we know the man is X^BY because he is an unaffected male. A man just needs one copy of the recessive allele to be affected, while females need two copies of the recessive allele. Therefore all of their daughters will receive an X from each parent, the X from their father will be dominant over the allele causing color-blindness, thus none of the daughters will be color-blind but all of their sons will be color-blind.