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1 Cards in this Set
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The gene for color blindness is X-linked recessive. One of the necessary conditions for a female to be color blind is:
(a) A mother who is colorblind. (b) A father who is colorblind. (c) A father and mother who are colorblind. (d) Neither parent to be colorblind, but both to carry the defective gene for colorblindness. |
Since color blindness is X-linked, and a female has two copies of the X chromosome, for her to be colorblind, she must receive two copies of the defective gene; one on each chromosome. Her mother must donate one defective copy and her father must donate one defective copy. Her father has only one X chromosome. Thus, if her father has a defective gene on the X chromosome, it will be passed on to his daughter. He must also be colorblind, since he has only one X chromosome. Her mother can have one or two defective copies, but she need not have two defective copies. Hence the father must be colorblind but the mother need not be colorblind. We can eliminate (A), (C), and (D). (B) remains.
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