The studies of mammalian chromosomes have constituted an effective area of investigation to explain their relationship. The entire chromosome set of a species is known as a karyotype. Many rodent species show a tendency for extensive chromosomal variability within species and species complexes. The use of molecular methods to provide more insight into the taxonomy and phylogeny of Cricetomys was recommended. Karyotypic studies were carried out on the African Giant rat, (Cricetomys gambianus, Waterhouse-1840) with the aim of determining its chromosome number, length, centromeric indices and nomenclature. The chromosomes were prepared from the conventional bone marrow of 10 African Giant rats – five male and five female Giant rats, treated intraperitoneally with 2 ml of 0.04% colchicines for 3 hours. Chromosomes in well-spread cells were counted and measured using KaryoType computer software. Arm lengths, centromeric indices and nomenclature were determined from these measurements and were expressed in micrometre (μm). The chromosomes were classified based on the centromeric indices obtained as metacentrics, submetacentrics, acrocentrics, subacrocentrics and telocentrics. Ideograms were also constructed from the measurements. Photomicrographs of well-spread mitotic metaphase chromosomes were used to construct a standard karyotype for the species. A diploid chromosome number of 2n = 80 with an autosomal fundamental number (NFa) of 66 to 95 were obtained for the species of C. gambianus used in this study. From the constructed idiogram, there was gradual decrease in length from one chromosome pair to another. The mean chromosomal arm lengths were siginificantly (P < 0.05) higher in the males compared to those of their female counterparts. There was no significant difference in the centomeric indices. The chromosomal nomenclatures were predominantly terminal. The chromosomal numbers, lengths, autosomal fundamental numbers and nomenclatures were similar with those xviii found in Benin Republic, Senegal, Niger Republic, Cameroun and other countries. The comparative species of the Texas banner-tailed Kangaroo rat, Dipodomys spectabilis has a diploid chromosome number of 2n = 72, and an autosomal fundamental number (NFa) of 70, which was closely related to that of the Cricetomys.
CHROMOSOMAL PATTERNS AND VARIABILITY IN THE AFRICAN GIANT RAT (Cricetomys gambianus, WATERHOUSE-1840)