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ID: 35265 • Letter: P
Question
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On average, what proportion of the genome in two full sisters (sisters who have the same two biological parents) would be exactly the same? Assume no crossing over occurs. Note: The question is restricted to considering sisters to avoid the complication of the sex chromosomes. Your answer should be expressed as a %. 3. (5 pts.) Gregor and Barbara are planning to have children, but they?re co cerned because Gregor?s brother has galactosemia (an autosomal recessive disease). Coincidentally, Barbara recently discovered that her great-grandmother had; iso bad galactosemia. Barbara has a sister who has three, healthy children (i.e. no actosemia). What is the probability that Gregor and Barbara?s first child will have galactosemia? Express your answer as a reduced fraction.Explanation / Answer
1)
The rules of autosomal recessive condition are:
So, based on the given data, both gregor and Barbara does not affected, thus they may be normal or carriers.
Gregor bother has disease (complete heterozygous), hence Gregor mother and father are carriers and his grandparents are affected, thus Gregor is a carrier for the trait. Barbara great grandmother had disease, hence Barbara mother or father may be affected, and hence it passed to the Barbara and her sister. But, her sister may be not received (25% are normal), hence her children’s do not have this trait.
Hence, both Barbara and Gregor are carriers. So, the first child has 1/4th or 25% chance of occurrence.