Chromosome profile of Indian elephants ( Elephas maximus indicus)

Abstract

A karyological study in Indian elephants using peripheral venous blood collected from 7 tuskers, 7 cow elephants and one makhna belonging to some temples and private owners of Trichur District was undertaken with objectives of a) to evolve a technique for chromosome studies of elephants. b) to find out the chromosome number in Indian elephants, and c) to suggest sex chromosome mechanism in sex determination. Standardization of technique Comparison of efficacy of phytohaemagglutinin – M (Difco) and Poke – weed mitogen (GIBCO), in two different culture media namely TC 199 and RPMI – 1640, as mitogens showed that phyto – haemagglutinin – M yielded a mitotic index of 0.33 and 0.66 per cent in medium TC 199 and RPMI – 1640 respectively; poke – weed mitogen yielded a mitotic index of 5.33 and 5.66 per cent respectively in TC 199 and RPMI – 1640. Statistical analysis revealed that the efficacy of the two different media used was not significantly different, whereas the efficacy of two mitogens differed significantly at five per cent level. Poke – weed mitogen was found to be better than phytohaemagglutinin – M as far as indusing mitoses in elephant lymphocyte cultures over a 72 hour culture period was concerned. Colchicine treatment using 0.1 ml colchicine solution (0.0001%) for a period of one hour yielded satisfactory chromosome preparations. Karyotype The karyotype of the tusker, cow elephant and makhna revealed a diploid chromosome number of 2n = 56, comprising of 54 autosomes and 2 sex chromosomes. The autosomes were classified into 6 submetacentric and 21 acrocentric chromosomes. The X – chromosome was a submetacentric in all the three groups of elephants whereas the Y – chromosome was a small acrocentric in the tusker as well as the makhna. Analysis of relative length of chromosomes showed that the largest chromosome pair measured a relative length of 6.973 per cent and the smallest chromosome was the Y – chromosome measuring a relative length of 1.710 per cent. Position of centromere on the basis of centromeric index suggested that the centromere was farthest from the centre of the chromosome in the second autosome pair and nearest to the centre in the X – chromosome among the submetacentric chromosomes. Neither autosomes nor sex chromosomes possessed satellites on karyological examination. The elephants studied exhibited XX/XY sex chromosome mechanism. The cow elephant possessed XX sex chromosome complement while both tusker and makhna possessed XY sex chromosome complement. A comparison between the karyotypes of tusker and makhna did not show any variation in (a) basic number, (b) relative length (C) position of centromere, (d) absence of satellites on the chromosomes and (e) the sex chromosome complement. It may be concluded that tusklessness in makhna is not associated with either euploidy or aneuploidy.