If children are born to a female with Down syndrome a normal male how many will have down syndrome?

Question

Trisomy 21 or Down syndrome occurs when there is a normal diploid chromosomal complement of 46 chromosomes, plus one extra copy of chromosome 21. Such individuals thus have 47 chromosomes. There is impaired fertility of both sexes, but females are more likely to be fertile than males. If children are born to a female with Down syndrome and a male with the normal complement of 46 chromosomes, what proportion of the offspring will be expected to have Down syndrome?

Answer 1

The chance that the offspring acquired an extra chromosome in chromosome 21 is 50%. But nondisjunction in chromosome 21 may occur in either meiosis I or meiosis II, which makes the probability that the offsprings will have the trisomy 21 syndrome.

Remember, Down's Syndrome is the effect of nondisjunction(failure of chromosomes to separate during either meiosis I or II) of chromosome 21 so anything can happen.

Answer 2

I don't know