How many chromosomes does a gray rat have? - briefly
The gray rat has a diploid chromosome number of 42. This consists of 21 pairs of autosomes together with the sex chromosomes.
How many chromosomes does a gray rat have? - in detail
The gray rat (Rattus norvegicus) possesses a diploid chromosome number of 42, arranged in 21 homologous pairs. This count includes 20 pairs of autosomes and one pair of sex chromosomes (XX in females, XY in males).
Chromosome composition:
- Autosomes: 20 pairs, numbered from the largest (pair 1) to the smallest (pair 20).
- Sex chromosomes: one X and one Y chromosome in males; two X chromosomes in females.
Karyotypic features:
- Metacentric and submetacentric morphology predominates among the larger autosomes.
- Subtelocentric and acrocentric forms appear in the smaller autosomes.
- The Y chromosome is the smallest element, lacking a homologous counterpart in females.
Methods used to establish the count:
- Giemsa staining of metaphase spreads from bone‑marrow or fibroblast cultures.
- Fluorescence in situ hybridisation (FISH) for precise identification of individual chromosomes.
Comparative context: other rodent species display different numbers, for example the house mouse (Mus musculus) has 40 chromosomes, while the Norway rat’s close relative, the black rat (Rattus rattus), also carries 42 chromosomes.
The established chromosome number forms the basis for genetic mapping, disease‑model development, and evolutionary studies within the species.