How many chromosomes does a house mouse have? - briefly
The house mouse (Mus musculus) possesses a diploid chromosome number of 40, organized as 20 homologous pairs. This count is consistent across laboratory and wild populations.
How many chromosomes does a house mouse have? - in detail
The house mouse (Mus musculus) possesses a diploid chromosome complement of 40, organized as 20 homologous pairs. Among these, 19 pairs are autosomes and one pair constitutes the sex chromosomes (XY in males, XX in females). The autosomal set includes a mixture of metacentric, submetacentric, and acrocentric chromosomes, with sizes ranging from the largest chromosome 1 (~5 % of the genome) to the smallest chromosome 19.
Karyotypic analyses of laboratory strains confirm the 2n = 40 count, although minor variations can occur in wild populations due to Robertsonian translocations that fuse two acrocentric chromosomes into a single metacentric chromosome. Such rearrangements alter the number of visible chromosomes but preserve the total genetic content.
The mouse genome is fully sequenced, allowing precise mapping of genes to specific chromosomal locations. Approximately 2.7 gigabases of DNA are distributed across the 40 chromosomes, with an average gene density of roughly 12 genes per megabase. This dense arrangement facilitates genetic studies, as recombination rates and linkage maps are well characterized for each chromosome.
In comparative cytogenetics, the mouse chromosome number contrasts with that of the human genome (46 chromosomes) and aligns closely with other rodents, which typically exhibit diploid numbers between 30 and 44. The conserved 2n = 40 in Mus musculus serves as a reference point for evolutionary investigations of chromosomal rearrangements across the Muridae family.