Down's syndrome is caused by an extra copy of | vedclass

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(D) Down's syndrome is a chromosomal disorder caused by trisomy of chromosome $21$. An affected mother has $47$ chromosomes (including an extra $21$st

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(D) Down's syndrome is a chromosomal disorder caused by trisomy of chromosome $21$. An affected mother has $47$ chromosomes (including an extra $21$st chromosome),while a normal father has $46$ chromosomes. During meiosis in the mother,the gametes produced will have either $23$ or $24$ chromosomes. Specifically,$50\%$ of the eggs will carry the extra $21$st chromosome. When these eggs are fertilized by normal sperm ($23$ chromosomes) from the father,$50\%$ of the resulting zygotes will have $47$ chromosomes (trisomy $21$),leading to Down's syndrome. Therefore,$50\%$ of the offspring are expected to be affected.

Down's syndrome is caused by an extra copy of chromosome number $21$. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder (in $\%$)?

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