Chimpanzees, gorillas, and orangutans have DNA sequences that are almost identical to those of humans; however, these genes are found on 24 pairs of chromosomes in apes, while humans have 23 pairs. The C2 chromosome in humans is a large chromosome with similar banding pattern and DNA sequences to two smaller chromosomes in apes (C2 and C4). In addition it appears to have both a vestigial second centromere and telomere sequences in the middle of the strand.
-What could explain these observations?
A)The human ancestor originally had 24 pairs but complete fusion of C2 and C4 occurred, reducing the total number of chromosomes.
B)A nondisjunction event must have occurred in the human ancestor, increasing the overall ploidy.
C)The loss of a chromosome is due to a deletion event in the human ancestor.
D)C2 must have undergone an inversion with C4.
E)There is not enough information to speculate.

Question

Quizplus · Accepted Answer

The similarities in DNA sequences and banding patterns suggest that the human ancestor originally had 24 pairs of chromosomes, but a fusion event occurred between C2 and C4, resulting in a reduced number of chromosomes in humans. The vestigial centromere and telomere sequences on C2 further support this hypothesis.

Chimpanzees, Gorillas, and Orangutans Have DNA Sequences That Are Almost