How many chromosomes does a rat have? - briefly
The common laboratory rat possesses a diploid chromosome number of 42 (2n = 42).
How many chromosomes does a rat have? - in detail
Rats possess a diploid chromosome complement of 42 chromosomes, arranged in 21 homologous pairs. The haploid set contains 21 chromosomes, including one pair of sex chromosomes (XX in females, XY in males).
The karyotype consists of:
- 20 autosomal pairs, numbered by decreasing size;
- One pair of sex chromosomes;
- A centromere position that varies among autosomes, producing metacentric, submetacentric and acrocentric forms.
Laboratory strains such as the Sprague‑Dawley and Wistar rats share the 2n = 42 configuration, although minor variations in chromosomal morphology have been recorded. Wild Rattus norvegicus individuals also maintain the same diploid number, confirming stability across the species.
The rat genome was sequenced as part of the Rat Genome Project, providing a reference assembly that maps each of the 42 chromosomes to specific genetic loci. This resource supports biomedical research by linking phenotypic traits to genomic regions, facilitating gene‑function studies and disease‑model development.