Question

Here I am stuck between B and D

22. If a gene is autosomal dominant, what pedigree traits does it show?

     A) If neither parent is affected, the offspring have a 25% probability of being affected

     B) One parent of an affected offspring must be affected

     C) If a parent is affected, approximately 25% of offspring will be affected

     D) If both parents are affected, 100% of offspring will be affected

Answer 1

B is thr answer.

*If neither parent is affected, then offspring has 25% of disease. This is the case of sutosomal recessive.

Parents: Aa × Aa

Gametes	A	a
A	AA	Aa
a	Aa	aa ( disease)

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B) The one parent should be affected, then offsprings are affected. Because the dominant allele is found only in affected individual in autosomal dominant trait. The parent has affected allele which is passed to the offspring which are also affected.

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C) If a parent is affected, then 25% if the offspring affected. It is not found in autosomal dominant trait.

For example: AA × aa

These parents have affected offspring only.

Aa × aa

In this case, 50% are affected which has Aa genotype.

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D) D is wrong because when Aa × Aa parents are found, then 75% are affected.

Similarly, AA × Aa parents have all affected offspring.

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Hence answer is B.