Chimpanzees, gorillas, and orangutans all have 48 chromosomes, whereas humans have 46. Human chromosome 2 is a large, metacentric chromosome with G-banding patterns that closely match those found on two different acrocentric chromosomes of the apes. Which statement would BEST explain these findings?
A) A translocation took place in a human ancestor, creating a large metacentric chromosome from the two long arms of the ancestral acrocentric chromosomes. The other small chromosome produced by this translocation was lost.
B) Meiotic nondisjunction gave rise to a nullisomic gamete. The fusion of two nullisomic gametes produced the ancestor of the human species with 46 chromosomes instead of 48.
C) A nonreciprocal translocation and subsequent fusion of the chromosomal fragments created a genome of 46 chromosomes without the loss of any genetic information.
D) Infection by a primate virus created a new chromosome when the viral DNA became a permanent part of the genome. Humans were not affected by this virus, so they did not acquire the extra chromosome.
E) Humans have the correct number of chromosomes. The extra chromosome pair in the other apes is a classic case of tetrasomy as a result of meiotic nondisjunction in the primate ancestor.

Question

Quizplus · Accepted Answer

The best explanation is that a translocation event in a human ancestor fused two acrocentric chromosomes into one metacentric chromosome, resulting in the reduction of chromosome number from 48 to 46.

Chimpanzees, Gorillas, and Orangutans All Have 48 Chromosomes, Whereas Humans