Question

4. Two healthy parents have nine healthy children, but their tenth child exhibits severe mental and physical issues. What is the most likely cause?


A. chromosomal inversion

B. Autosomal Recessive disease

C. Autosomal Dominant disease

D. Chromosome 21 Non-disjunction

E. All of the above

Answer 1

Answer- chromosome 21 non disjunction.

Nondisjunction of chromosome 21 results in Down's syndrome which results in mental retardation , physically stunted growth , mongoloid appearence . It is a chromosomal abnormality due to an extra arm or part of chromosome 21 . The parents will be healthy.

However , it could also be an autosomal recessive disorder because in autosomal recessive disorders if parents appear healthy and even one child is affected ,its because parents are Heterozygous for the condition so appear normal and 25% chance the offsprings might be affected . Affected child from healthy parents is charecteristic of autosomal recessive trait.

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