Mukundan, GRaghunandanan, K VKAU2020-10-232020-10-231988171011https://krishikosh.egranth.ac.in/handle/1/5810153682PhDA study was undertaken to evaluate and compare the chromosomal status of Local non – descript, half – bred Jersey, half – bred Holstein Friesian and Jersey cattle and to assess the incidence of chromosomal aberrations causing physiological disorders. The cattle owned by Kerala Agricultural University. Indo – Swiss Project and farmers formed the material for the study. In all, 102 animals consisting of 71 normal and 31 abnormal, were subjected to the study. Peripheral blood leukocyte culture technique with heparinised whole blood was used for chromosome analysis. The medium was TC 199 with phytohaemagglutinin M as mitotic inducer and colchicine as mitotic arrester. The cells in metaphase were harvested and air dried smears stained with Giemsa. Good spreads were photographed and karyotypes prepared. The efficiency of medium was tested using mitotic drive and mitotic index, which were between 32 to 33 per cent and 5 to 6 per cent respectively. Colchicine treatment of 0.1 ml (0.0001%) for 1 hour yielded clear visible chromosome spreads. The blood samples stored for varying time at 50C indicated that the whole blood transported in ice bath (50 C) is to be used within 12 hours after collection for lymphocyte culture. In normal cattle, diploid chromosome number was found to be 2n = 60 with 29 pairs of autosomes and one pair sex chromosome. The males were heterogametic. All the autosomes were acrocentric in Local, half – bred Jersey, half – bred Friesian and Jersey whereas the x chromosome was biarmed and a large submetacentric in all the genetic groups. The Y chromosome was polymorphic being acrocentric in Local and submetacentric in exotic bulls. No satellite was observed in any of the chromosomes. The relative length of largest and smallest autosomes were 6.5080 and 1.3473 per cent in Local, 6.4735 and 1.2250 per cent in half – bred Jersey, 6.2190 and 1.3788 per cent in half – bred Friesian and 6.9125 and 1.3096 per cent in Jersey respectively. The difference in relative length of autosomes between different genetic groups was not found to be significant. The relative length of x chromosome was 7.2838 per cent, 7.0313 per cent, 6.5138 per cent and 6.3166 per cent in Local, half – bred Jersey, half - bred Friesian and pure Jersey respectively. The differences between genetic groups were significant. In the karyotypic array based on relative length, the x chromosome occupied a first position in Local, half – bred Jersey, half – bred Friesian whereas in Jersey it was in between first and second pair of autosomes. The relative length of Y chromosome was 2.9415 per cent, 2.5745 per cent and 2.9375 per cent in Local, Jersey and Holstein Friesian respectively. The difference Local and Holstein Friesian was not significant. In karyological array the Y chromosome occupied a position between 15th and 16th pair of autosomes in Local and Holstein Friesian whereas in Jersey it was between 15th and 20th pair. The arm ratio of x chromosome was 2.043, 1.986, 1.739 and 1.690 in Local, half – bred Jersey, half – bred Friesian and Jersey respectively. In Local cattle the centromere was located away from mid point compared to other genetic groups. The distance between mid point and centromere was lowest in Jersey. The arm ratio of Y chromosome of Jersey and Holstein Friesian was 1.21 and 1.66 respectively. The location of centromere in Y chromosome of Jersey was more towards centre than that of Holstein Friesian. The centromere index of x chromosome was 0.365, 0.329, 0.338 and 0.372 in Local, half – bred Jersey, half – bred Holstein Friesian and Jersey respectively. The values for the centromere index confirm the findings obtained for arm ratio with regard to the proximity of centromere to the mid point of the chromosome. Among the 31 abnormal cattle, chromosomal aberration were observed in one 4 ½ years old sterile Jersey heifer, one Free martin and one Local bullock with abnormally developed secondary sexual characters. Infertile cattle showing repeat breeding, poor semen quality and poor libido did not exhibit any aberration. In the sterile Jersey heifer, 59/60 mosaicism was observed. The Free martin exhibited 60 XX/60 XY chimaerism having 14 per cent of the cells with XY type and others with XX type. The local bullock revealed abnormal development of teats and secretion of milky fluid. The mitotic spreads were of tetraploid nature (4n = 120) in 4.5 per cent cells and the diploid (2n = 60) in others. This animal was diploid tetraploid chimaera or mixoploid. The present study brought out findings that relative length, position in the karyotypic array, arm ratio and centromere index of sex chromosomes shall serve as tool for identification of inter – breed differences and that the occurrence of tetraploidy stimulate the activity of the female secondary sexual characteristics in male cattle.EnglishThesis