Humans have 46 chromosomes, whereas chimpanzees have 48 chromosomes in their diploid body cells. This means humans have 23 homologous pairs and chimpanzees have 24 pairs.
Species | Diploid body cell | Haploid gamete |
|---|---|---|
Human (Homo sapiens) | 46 chromosomes: 23 pairs | 23 chromosomes |
Chimpanzee (Pan troglodytes) | 48 chromosomes: 24 pairs | 24 chromosomes |
The difference is explained by a chromosome fusion in the human evolutionary lineage. Two chromosomes found separately in other great apes correspond closely to human chromosome 2. In an ancestor of humans, these two ancestral chromosomes fused end to end, reducing the diploid chromosome number from 48 to 46 without necessarily causing a major loss of genetic information.
Several observations support this explanation. Human chromosome 2 has DNA sequences resembling telomeres, normally located at chromosome ends, within the chromosome. It also contains evidence of a second, inactive centromere, consistent with two ancestral chromosomes becoming one. Its gene sequences and banding patterns correspond to those on two separate chimpanzee chromosomes.
A common misconception is that more chromosomes mean a more complex or more advanced organism. This is incorrect: chromosome number does not measure biological complexity. Humans and chimpanzees remain genetically similar because chromosome fusion mainly changed how genetic material was packaged, not the presence of every gene.
Exam technique: This is part of A3.1, Diversity of organisms, for both SL and HL. For a question asking you to state the numbers, give 46 for humans and 48 for chimpanzees. If asked to the difference or , link human chromosome 2 to fusion and support the claim using internal telomere sequences, the inactive centromere, or corresponding chromosome sequences.
