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. What would best explain these findings?
a) 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.
b) A Robertsonian 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.
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) 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.
