Genetic characterisation of buffaloes in Kerala using cytogenetic technique

Abstract

Buffaloes from four districts of Kerala formed the materials for this study. Blood samples were collected from external jugular/ear vein, in heparinised tubes. The technique employed was peripheral leukocyte culture technique. Out of the three different mitogens viz., pokeweed mitogen (PWM), phytohemaggultinin (PHA). and a mixture of these two. the mixture of PWM and PHA was found superior in inducing mitosis. A significant interaction between the mitogens and time of addition of mitotic arrester into the medium was observed. The mixture of PWM and PHA at an incubation time of 71 hours was found to produce best results in culture of buffalo lymphocytes followed by PWM at 70 hours. Ideal concentration of colcemid as mitotic arrester in this study was found to be 2 µg and 3 µg per ml of culture media, when the time of action of colcemid was retained for one hour.

Out of the 54 animals studied 45 had 2n=50, 5 had 2n=48 and rest 4 had 2n=49. In all the three chromosome types of animals 10 submetacentric chromosomes were observed. The sex chromosomes were similar in all the three types. Number of acrocentric autosomes was 38, 36 and 37 in the three classes respectively. The buffaloes having diploid chromosome number of 49 had two non homologues submetacentric chromosomes, one being the largest of the whole complement and one acrocentric was without a pair. The longest submetacentric autosome of swamp type had a relative length of 6.925+0.152 whereas in river type it had a relative length of 7.228+0.094. The smallest submetacentric autosome was having an average relative length of 4.911+0.118 and 5.05+0.107 in swamp type and river type respectively.

Relative lengths of longest acrocentric autosome in swamp type and river type were) 4.953+0.13 and 4.618 + 0.095 respectively. The shortest acrocentric in swamp type showed a relative length of 2.301+0.034 whereas in river type the shortest chromosome had a relative length of 2.064+0.275. The X chromosome was largest acrocentric chromosome of the complement. The Y chromosome was acrocentric and took a position of 22 in descending order based on relative length in the river buffaloes, whereas it occupied 20th position in swamp type. The X chromosome in swamp type had the relative length of 6.228 + 0.099 and that of river type was 6.220+0.136. The Y chromosome of swamp type and river type had relative length of 2.675+0.188 and 2.550+0.095 respectively. In terms of relative length X chromosome occupied fourth position in comparison to submetacentric autosomes of river type, whereas it was third position in swamp type. In swamp buffaloes arm ratio ranged from 1.479+0.055 in fifth to 2.183+0.169 in first submetacentric autosome. In river type the largest arm ratio was 2.289+0.221 in first chromosome and the smallest was 1.542+0.158 in fifth chromosome. The highest centromere index of 40.4+0.9 was obtained for fifth chromosome and the smallest centromere index of 33.2 + 2.1 was for first chromosome of swamp type. In river buffaloes fifth chromosome had a centromere index of 40.4+1.9 and first chromosome had the centromere index of 31.2+2.4. The observation of chromosome polymorphism in buffaloes of Kerala State have to be borne in mind prior to drawing breeding strategies in buffaloes for improved production potential and productive efficiency.