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?
Down's syndrome is the result of trisomy in which chromosome number $21st$ contains an extra copy of chromosome $(2 A+1)$ Affected mother will produce $50 \%$ normal egg cells and rest $50 \%$ eggs are of abnormal type. In normal case
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$n$-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.
Mendelian Disorder is a type of genetic disorder that is caused due to alterations in one gene or abnormalities in the genome. These disorders can be seen since birth and can be deduced using the Pedigree Analysis.
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