AP BIOLOGY

HEREDITY

MULTIPLE ALLELES

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Look at this cross:XB XB and Xb YWhat proportion/percent of the male children are colorblind?
A
100%
B
75%
C
25%
D
0%
Explanation: 

Detailed explanation-1: -It’s estimated that up to eight per cent of boys have some degree of colour blindness (also known as colour vision deficiency or CVD), whereas less than one per cent of girls do. That’s about one in 12 boys, and around one in 200 girls. What causes colour blindness?

Detailed explanation-2: -If it is only present on one, the female will only be a carrier and likely not express the trait. Since males only have on X chromosome, if it is present, it will be expressed. So if a female is color blind, her genotype would be XbXb, and a man with normal vision would have the genotype XBY.

Detailed explanation-3: -Males have 1 X chromosome and 1 Y chromosome, and females have 2 X chromosomes. The genes that can give you red-green color blindness are passed down on the X chromosome. Since it’s passed down on the X chromosome, red-green color blindness is more common in men.

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