How many chromosomes does a black rat have? - briefly
The black rat (Rattus rattus) has a diploid chromosome count of 42.
How many chromosomes does a black rat have? - in detail
The black rat (Rattus rattus) has a diploid chromosome complement of 42 (2n = 42). This number is consistent across most laboratory and wild populations studied to date.
The karyotype consists of:
- 21 pairs of autosomes, ranging from large metacentric to small acrocentric chromosomes.
- A single pair of sex chromosomes, with the male genotype XY and the female genotype XX.
Chromosome analysis has been performed using standard G‑banding and more recent fluorescence in situ hybridization (FISH) techniques. These methods confirm the presence of 20 metacentric or submetacentric autosomes and one small acrocentric pair. The sex chromosomes are typically identified by their distinct size and banding patterns.
Comparative cytogenetics shows that the chromosome count matches that of the common house mouse (Mus musculus) but differs from the brown rat (Rattus norvegicus), which has 42 chromosomes as well but displays a slightly altered morphology of the smallest autosomes.
Variations such as minor structural rearrangements (e.g., pericentric inversions) have been reported in isolated populations, yet the overall diploid number remains unchanged. No viable polyploid or aneuploid forms have been documented in natural settings.
Understanding this chromosomal configuration aids in taxonomic classification, evolutionary studies, and the interpretation of genetic experiments involving Rattus rattus.