Solutions For An Introduction to Genetic Analysis Chapter 3 Problem 55P

The most probable explanation for the above pedigree would be that the mother in generation I experienced a mutation in a progenitor cell of her egg cells. The two males of generation II who died received egg cells that had undergone cytoplasmic segregation of defective mitochondria before fertilization. The two females of the same generation received a mixture of both defective and normal mitochondria.

The spontaneous abortion seen in the first lady of generation II was due to extensive cytoplasmic segregation in her germ cells. The defective mitochondria were accumulated in the zygote resulting in fetal abortion.

The spontaneous abortion seen in the second lady of generation II is also due to the same reason. This lady had two normal children which were result of opposite cytoplasmic segregation. The normal mitochondria were accumulated. This woman also shows three affected children who later died. This was due to partial cytoplasmic segregation in the egg stage. So fetal abortion was not seen.