Chromosome Number

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True Likely Speculative

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Humans have 23 pairs of chromosomes while great apes have 24 pairs. Human chromosome 2, a large metacentric chromosome, is the product of a fusion between two smaller telocentric chromosomes found in the other great apes. This fusion resulted in humans having one less chromosome pair than apes. Remnant sequences of telomeres can be identified at the fusion point in band 2q13. Remnants of the second (now inactive) centromere are present in bands 2q21.3 to 2q22.1.

The Human Difference:

Humans carry one fewer chromosome than chimpanzees, bonobos, gorillas and orangutans. The human difference is a derived feature.

Universality in Human Populations:

The chromosome number is universally shared among humans.

Mechanisms Responsible for the Difference:

The creation of human chromosome 2 involved fusion of two smaller telocentric chromosomes.

References:

Peter S. Harper: First Years of Human Chromosomes. The Beginnings of Human Cytogenetics. Scion Publishing, 2006.
Yunis and Prakash (1982). "The origin of man: a chromosomal pictorial legacy". Science 215: 1525–1530. doi:10.1126/science.7063861. PMID 7063861

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