How many chromosomes does a decorative rat have? - briefly
A decorative rat has a diploid chromosome number of 42, identical to that of the standard laboratory rat (Rattus norvegicus). This reflects the species’ conserved karyotype.
How many chromosomes does a decorative rat have? - in detail
The domestic ornamental rat, derived from Rattus norvegicus, possesses a diploid chromosome complement of 42 (2n = 42). This count matches that of the wild Norway rat and reflects the species’ conserved karyotype across laboratory and pet lines.
Key characteristics of the rat karyotype include:
- Six pairs of large metacentric chromosomes (pairs 1–6)
- Six pairs of medium-sized submetacentric chromosomes (pairs 7–12)
- Six pairs of small acrocentric chromosomes (pairs 13–18)
- One pair of sex chromosomes: XX in females, XY in males
The chromosome number remains stable in breeding programs; spontaneous aneuploidies are rare but can arise from mutagenic exposure or chromosomal rearrangements, occasionally producing viable sublines with altered phenotypes.
Research on the genome of ornamental rats confirms that the 42‑chromosome set carries approximately 2.75 Gb of DNA, encoding roughly 23,000 protein‑coding genes. This genomic architecture underlies the species’ suitability for genetic studies and contributes to the predictable inheritance of coat color, pattern, and other traits valued by hobbyists.