Principles of Inheritance and Variation Question 179
179. 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?
(a) $25 %$
(b) $100 %$
(c) $75 %$
(d) $50 %$
Show Answer
Answer : d
Hints & Solution
(d) $50 %$ of ova will have $(n+1)$ chromosome which would, on fertilisation, yield abnormal zygotes $(n+1)+(n)=2 n+1$.
