Question

An achondroplastic male dwarf with 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. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.

How many of their sons would be color-blind and of normal height?
a.all
b.one out of four
c.none
d.three out of four
d.half

Answer 1

In the given scenario, half of the sons would be color-blind and of normal height because all sons would inherit color blindness from their mother, and have a 50% chance of inheriting the non-dwarf allele from their father.

Step-by-step explanation:

The question deals with two genetic traits: achondroplastic dwarfism, which is autosomal dominant, and red-green color blindness, which is X-linked recessive. The male in this scenario is a dwarf with normal vision and the female is of normal height but color-blind. Since achondroplastic dwarfism is dominant, all children of a dwarf will either be of normal height or dwarf, regardless of the height of the other parent. Therefore, normal height happens only if they inherit a non-dwarf allele from the achondroplastic dwarf parent.

About the color blindness, males have one X and one Y chromosome. If a male inherits an X chromosome with the color blindness allele, he will exhibit color blindness, since there is no corresponding gene on the Y chromosome to counter the recessive trait. In this case, as the mother is color-blind, all her sons will inherit her only X chromosome, which carries the color blindness allele. As such, all sons of this couple will be color-blind, but only half of them will be of normal height because they have a 50% chance of inheriting the non-dwarf allele from their father.