Refer to the following information to answer the questions below.

a man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. the man's father was 6 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.

what proportion of their sons would be color-blind and of normal height?

1/4

Explanation:

Let achondroplastic dwarfism be controlled by gene A

Let red green color blindness be controlled by gene Xc

Man : He is dwarf so he will be either AA or Aa since its a dominant trait.  His father had normal height so he must be aa. He will pass on one "a" allele to his son. Hence, the man's genotype is Aa. He has normal vision and colorblindness is recessive X-linked trait so his total genotype is AaXCY

Woman : She has normal height so her genotype is aa. She is colorblind hence her total genotype will be aaXcXc.

When,  

AaXCY   X   aaXcXc :

If we check the crosses individually:

    A     a

a  Aa   aa

a  Aa   aa

      XC      Y

Xc  XCXc  XcY

Xc  XCXc  XcY

All the sons will be colorblind (XcY) and half of the children will have normal height (aa). Out of these children half will be sons so total probability of having a colourblind son with normal height will be :

1 * 1/2 * 1/2 = 1/4

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