. Downs 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. 50%

b. 25%

c. 100%

d. 75%

Best Answer

Solution ||| Down’s syndrome is the result of trisomy in which chromosome number 21st contains an extra copy of chromosome (2A + 1) Affected mother will produce 50% normal egg cells and rest 50% eggs are of abnormal type. In normal case

downs syndrome is caused by an extra

n — normal egg

Fusion of normal egg with a normal sperm (comes from father) produces a normal offspring while fusion of abnormal egg with a normal sperm will produce an abnormal offspring.

 

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