A mother has Down syndrome,and the father is | vedclass

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(C) Down syndrome is a chromosomal disorder caused by the presence of an extra copy of chromosome $21$ (trisomy $21$).In a mother with Down syndrome,t

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(C) Down syndrome is a chromosomal disorder caused by the presence of an extra copy of chromosome $21$ (trisomy $21$).In a mother with Down syndrome,the genotype is $47, XX, +21$.During meiosis,the mother produces two types of gametes: $50 \%$ with $23$ chromosomes (normal) and $50 \%$ with $24$ chromosomes (containing the extra chromosome $21$).The father is normal $(46, XY)$,producing normal gametes with $23$ chromosomes.When the mother's gamete with $24$ chromosomes fuses with the father's normal gamete ($23$ chromosomes),the resulting zygote will have $47$ chromosomes,leading to Down syndrome.Since $50 \%$ of the mother's gametes carry the extra chromosome,there is a $50 \%$ probability that the offspring will inherit the condition.

$A$ mother has Down syndrome,and the father is normal. What is the probability of their offspring having Down syndrome (in $\%$)?

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