Principles Of Inheritance And Variation Ques 160
160. 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?
25%
(b) 100%
75%
50%
Show Answer
Answer : d
Hints & Solution
(d) 50% of ova will have $(n+1)$ chromosomes which would, on fertilisation, yield abnormal zygotes $(n+1)+(n)=2n+1$.
BETA
