Question

15) Colorblindness is an X-linked recessive trait (“D” results in normal vision, whereas “d” results in colorblindness). A man has normal color vision. In addition, he is heterozygous (Bb) for an autosomal gene that causes extreme sensitivity to strep throat when homozygous recessive. a) What proportion of his sperm will be “bD”? b) If he marries a woman who is heterozygous for both traits, what proportion of their children will be daughters that are colorblind and sensitive to strep throat? c) What proportion of the children from part b will be sons that are colorblind and sensitive to strep throat?

Answer 1

Male genotype : X^D Y Bb

Gametes: X^DB, X^Db,  YB, Yb

Ansa) Proportion of sperm will be bD or bX^D is =1/4

Ansb) p genotype: X^DX^d Bb. x X^D Y Bb

Gametes : X^DB, X^Db,X^d B, X^db X^DB, X^Db, YB, Yb

F1

XDXDBB	XDXDBb	XDXdBB	XDXdBb
XDXDBb	XDXDbb	XDXdBb	XDXdbb
XDYBB	XDY Bb	XdY BB	XdY Bb
XDYBb	XDY bb	XdY Bb	XdY bb

Proportion of their daughter to be both colourblind and sensitive to sreppthroat is 0.

C) Proportion their son to be colourblind and sensitive tostrep throat is1/8.