Abstract
The diploid chromosome number in the common house rat of Allahabad, Rattus rattus rufescens Gray., is 42 with XX/XY sex determining mechanism. The autosomes consists of 13 pairs of telocentrics (T or t) and 7 pairs of metacentrics (M or m). X is a medium-size, telocentric (T), ranking 5th or 6th in the order of length, in the complement, and constitutes 5.55 % of the total haploid length. Y is variable in size. Several karyotypic anomalies, such as the presence of an unpaired, large Sin or T chromosome, heteromorphic pair 1, close association of one of the homologues each of pairs 7 and 4, 7 and 12 and pair I and a large telocentric chromo-some, are reported.
