Cytogenetic Studies of Malayan Gaur (Bos Gaurus Hubbacki), Sahiwal-Friesian Cattle and Their Hybrid Backcrosses

In early April 1983, a stranded Malaysian gaur (Bos gaurus hubbacki) mated with a group of Sahiwal-Friesian dairy heifers and this resulted in the birth of an inter-specific hybrid calf named SELEMBU. In this study, chromosome analysis of four Malayan gaur (Bos gaurus hubbacki), ten Sahiwal-Friesian cattle and seven hybrid backcrosses was undertaken to determine their karyotype status and differences. The gaur and cattle has chromosome complements of 2n = 56 and 2n = 60, respectively. Two types of chromosomal arrangements of the backcrosses were observed; namely an intermediate to the parental species (2n = 58) and a cattle type (2n = 60). The backcrosses with 2n = 60 shared similar chromosomal arrangement and banding characteristics of the cattle. Backcrosses with 2n = 58 exhibited the non-homology of two submetacentric and two acrocentric autosomes, where the variations were inherited from the parental species that possessed different karyotypes. A comparison of the gaur with cattle, as the model of the ancestors of the modern bovids, showed structural and characteristic differences in their karyotypes. The gaur exhibited two pairs of submetacentric chromosomes and lacked two chromosome pairs, which had resulted from Robertsonian translocations during their karyotype evolution. Banded karyotypes revealed extensive similarities of chromosomes 1 and 2 of the Malayan gaur to the homologous acrocentric chromosomes of cattle. For the first time, chromosome 1 of the gaur was identified to contain an ancient origin inverted segment compared to cattle, which was homozygous in all the studied gaur samples. The intensity of the C-bands on chromosomes 1 and 2 suggested that the translocations occurred at different periods of time during the karyotype evolution.

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