Karyological studies vis-à-vis wool quality traits in Nali, Munjal and Crossbred sheep
Abstract
Karyological studies were made on somatic chromosomes in Nali, Munjal and Crossbred sheep.
A total number of 50 animals screened for cytogenetic studies and 115 animals for analysing wool
quality traits. In vitro whole-blood-culture technique was employed for the preparation of somatic
metaphase chromosomes. Relative lengths of autosomes and sex chromosomes were compared in three
groups. Morphometric measurements like arm ratio and centromeric index were also analysed
comparatively. Model karyotypes and ideograms were constructed on the basis of morphological
homology and bandings (G-and Ag NORs). Somatic metaphase chromosomes in all the three groups
reaffirms diploid count of fifty- four (2N=54). Among the 26 pairs of autosomes, first 3 pairs of
chromosomes were metacentric/sub metacentric type. Rest 23 pairs of autosomes were acrocentric
type. The similar pattern of chromosomes between the Nali Munjal and Crossbred sheep was observed
for the shape of autosomes and sex chromosomes. The chromosomes (autosomes and sex
chromosomes) were linearly differentiated for morphometric analysis into three groups on the basis of
size and shape. Group ‘A’ consisted of 3 pairs of large sub metacentric autosomes, and group ‘B’
consisted of rest (4 to 26 pairs) of acrocentric autosomes. The ‘C’ group comprised of the sex
chromosomes X and Y. The centromeric indices for the first 3 pairs of autosomes showed small but
non-significant differences among Nali, Munjal and Crossbred sheep. Among the three chromosome
pairs the centromeric indices showed descending trend with the lowest value for third chromosome
pair. However, the arm ratio showed reverse trend with lowest value for the third pair and highest value
for the first pair with an indication of the chromosomes to be exhibiting metacentric type of shape from
its sub metacentric type. G-banding pattern of chromosomes was similar in Nali, Munjal and Crossbred
sheep. Ag-NOR banding revealed five pairs of chromosomes possessing NOR sites in all groups. High
resolution banding revelled presence of lesser number of bands in Crossbred sheep as compared to
indigenous sheep breeds. Wool quality traits study lead to conclusion that Nali and Munjal differ
significantly from Crossbred sheep in terms of their wool quality parameters. These three breeds shared
no specific chromosomal landmarks for their differences in wool texture.