Question

this pedigree is showing colorblindness which is sex - linked recessive.
what is the genotype of an affected male?
○ ( x^{b}x^{b} )
○ ( x^{b}y )
● ( x^{b}y )
○ ( x^{b}x^{b} )

Explanation:

Step1: Analyze the sex - linked recessive trait

Colorblindness is a sex - linked recessive trait. Males have one X and one Y chromosome (\( XY \)).

Step2: Determine the genotype of an affected male

For a male to be affected (show the recessive trait), he must have the recessive allele on his X chromosome. Let \( X^{b} \) represent the recessive allele for colorblindness. So the genotype of an affected male is \( X^{b}Y \).

• \( X^{b}X^{b} \) is the genotype of an affected female (not male).
• \( X^{B}Y \) is the genotype of a normal male.
• \( X^{B}X^{b} \) is the genotype of a carrier female (not male).

Answer:

C. \( X^{b}Y \)