Karyotype of the mouse (Mus musculus)

The standard karyotype of the mouse consists
of 19 chromosome pairs in addition to the X and
Y chromosomes. All chromosomes except the X
and Y are telocentric and of similar size (1).
However, they differ in their banding patterns,
characteristic for each chromosome pair, and
therefore are individually distinct. Certain
strains of mice may show variants of the karyotype
(2). These variants arise from fusion of certain
of the chromosomes. In the example shown
here, only chromosome pairs 1, 15, 19, and X
correspond with those of the standard karyotype,
while the others consist of fused chromosomes,
e. g., chromosomes 4 and 2, chromosomes
8 and 3, etc. Structural rearrangements
of the karyotype occurred with the separation
of different species in evolution.