Question

Which of the following would not be observed in a pedigree if a genetic disorder was inherited in a recessive manner?

A. Two unaffected parents have an affected offspring.
B. Two affected parents have an unaffected offspring.
C. One affected and one unaffected parent have an unaffected offspring.
D. All of the above are possible for a recessive disorder.

Answer 1

Option B, where two affected parents have an unaffected offspring, would not be observed in a pedigree if a genetic disorder was inherited in a recessive manner, since affected individuals must have two copies of the recessive allele.

Step-by-step explanation:

In the context of a genetic disorder inherited in a recessive manner, option B (Two affected parents have an unaffected offspring) would not occur. When a disorder is recessive, affected individuals must have two copies of the recessive allele (homozygous recessive). Therefore, if both parents are affected, they would not have an unaffected offspring since they can only pass on the recessive allele associated with the disorder.

Two unaffected parents having an affected offspring (option A) is possible if both parents are carriers (heterozygous), and one affected and one unaffected parent have an unaffected offspring (option C) is also possible if the affected parent is homozygous recessive and the unaffected parent is homozygous dominant.