Down syndrome is caused by an extra chromosom | vedclass

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(A) Down syndrome is a chromosomal disorder caused by trisomy of chromosome $21$ ($47, XX, +21$ or $47, XY, +21$).In an affected mother (trisomic,$2n+

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$50$

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(A) Down syndrome is a chromosomal disorder caused by trisomy of chromosome $21$ ($47, XX, +21$ or $47, XY, +21$).In an affected mother (trisomic,$2n+1$),the gametes produced will be $n$ and $n+1$ in equal proportions ($50\%$ each).When these gametes fuse with normal gametes $(n)$ from a normal father,the resulting offspring will be $2n$ (normal) and $2n+1$ (affected) in a $1:1$ ratio.Therefore,$50\%$ of the offspring are expected to inherit the extra chromosome and exhibit the disorder.

Down syndrome is caused by an extra chromosome in the $21$st pair. What percentage of offspring from an affected mother and a normal father will show the effect of this disorder (in $\%$)?

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