Abstract
Chromosomes were studied in regenerating cells derived from 5 partially hepatectomized rats weighing 240 to 360g. Several previous investigators have reported that polyploid cells occurred in the regenerating rat liver at more than 40% of metaphase cells in cell population (Biesele 1944, Makino and Tanaka 1953, Gläss 1958). However, the frequency of the polyploid cells in the present study were found to be substantially lower than the reported cases by the previous workers; it was only 11.2% on an average ranging from 22 to 3 per cent. Aneuploid cells were also very few in number, and most of the cells observed had a normal diploid number of the rat (2n, 42).
Detailed karyotype analyses were made on well-spread metaphase cells taken from the regenerating liver and supplementally on those from the normal embryonic liver grown in vitro. The results showed that all of the diploid cells analyzed had a normal chromosome constitution of the rat. Two representative karyotypes were shown in Figs. 1 and 2. As shown in the figures, the chromosomes can be classified into 5 different autosomal groups (I-V) and the sex elements. The X chromosome was recognized as one of the acrocentrics which ranks between the 3rd and 4th autosomal pairs. The Y chromosome was identified in the male complement to the smallest acrocentric element approximately corresponding in size to the 17th autosomal pair. The results of the karyotype analyses are in general agreement with those reported by Tjio and Levan (1956), Makino (1957) and particularly by Hungerford and Nowell (1963).
