Trisomy of chromosome No 13 in spontaneous mammary tumors of GR, C3H, and noninbred Swiss mice.

Karyotype analyses were conducted on spontaneous mammary tumors of 11 GR, 2 C3H, and 2 noninbred Swiss mice with the use of trypsin-Giemsa banding procedures. All tumors manifested trisomy of chromosome No 13 in most cells, and all except 1 tumor had cells with a model chromosome number of 40.