HEREDITY
LINKED GENES
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Barbara’s mother must have been colorblind.
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Bill’s mother must have been colorblind.
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Barbara’s father must have been colorblind.
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Bill must be colorblind.
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Detailed explanation-1: -For example, if a mother is a carrier for colorblindness (X+Xc), and a father has normal vision X+Y, then their sons have a 50% chance of colorblindness because they inherit their X chromosome from their mother and their Y chromosome from their father.
Detailed explanation-2: -Females have 2 X chromosomes, one from their mother and one from their father. To have red-green color blindness, both X chromosomes would need to have the gene for red-green color blindness.
Detailed explanation-3: -C is the dominant colour vision allele. c is the recessive counterpart. The genotype of a woman who is colour blind is XcXc. This is because she colour blind, and carries two X-linked colour vision allele.
Detailed explanation-4: -Answer and Explanation: For a female to be red-green colorblind, she must have two recessive alleles since colorblindness is a recessive condition. Therefore, her genotype would have to be X*X* (where * represents the mutated allele). Since she got one allele from each parent, her mother could be either X*X* or X*X.