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Question
A man and a women who both appear normal have a child together, who has sickle cell anaemia. Sickle cell anaemia is an autosomal recessive trait. The woman becomes pregnant again and is told that she is carrying fraternal twins. What is the probability that both of the couple's twins will develop sickle cell anaemia
A man and a women who both appear normal have a child together, who has sickle cell anaemia. Sickle cell anaemia is an autosomal recessive trait. The woman becomes pregnant again and is told that she is carrying fraternal twins. What is the probability that both of the couple's twins will develop sickle cell anaemia
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Solution
The correct option is A 1/16
Fraternal twins are two different eggs fertilized to different zygotes. Let the recessive gene be "a". The genotype of the first child is "aa" as he/she is affected by the disease. This implies that normal parents could be of Aa genotype. The probability of having an infected progeny is 1/4 according to the cross between parents. Hence, for two children(fraternal twins individual fertilized eggs), the probability will be (1/4)*(1/4)=1/16.
So, the correct option is '1/16'.
Fraternal twins are two different eggs fertilized to different zygotes. Let the recessive gene be "a". The genotype of the first child is "aa" as he/she is affected by the disease. This implies that normal parents could be of Aa genotype. The probability of having an infected progeny is 1/4 according to the cross between parents. Hence, for two children(fraternal twins individual fertilized eggs), the probability will be (1/4)*(1/4)=1/16.
So, the correct option is '1/16'.
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