Profiling of Chromosomal Complement in Nandidurga Goats of Karnataka

Goat was the first animal to be domesticated at the dawn of Neolithic period around 10,000 years ago. Goat farming offers much needed income generation to millions of marginal and landless laborers. The Indian goat population was about 47 million in 1952 and has expanded to 148.88 millions in 2019 (Anonymous 2019). India is bestowed with 34 registered goat breeds and many non-descript goats which have high production potentialities and are yet to be characterized (Phenotypic, Cytogenetic and Molecular). In Karnataka, the goat population has continuously increased over the years from 3.7 million in 1972 to 6.17 million in 2019 (Anonymous., 2019). Karnataka is ranked tenth in the country with regard to goat population and has increased by almost 28.63 per cent compared to the population status in 2012.
 
Cytogenetic characterization is crucial in identifying the breed and forms the basis for molecular genetic characterization (Ekambaram et al., 2011). Cytogenetics provides a simple and easier approach for characterizing a breed and helps in conservation of indigenous breeds. It enables the correct identification of individual chromosomes and establishes standard karyotype which is essential for characterization of any breed (Stranzinger and Fechheimer, 1989). Also, cytogenetic studies help in selection of animals free from chromosome abnormalities (abnormal body conformation, lower fertility or sterility). The chromosomal profiling will ultimately aids in evaluating reproductive health and fertility status of breeding animals at an earlier age (Basumatary, 2003). Keeping this in view, the technique of short term lymphocyte culture for Nandidurga goats was standardized and various morphometric measurements of chromosomes and idiogram were established.

Present study was conducted on Nandidurga goats maintained by farmers in their breeding tract. This research was conducted at Department of Animal Genetics and Breeding, Veterinary College, Bengaluru (KVAFSU) during the year 2019-2020. Total of 10 goats (5 bucks and 5 does) were identified randomly from the breeding population. About 2 ml blood was collected from the jugular vein using heparinised vacutainers and was carried to laboratory in ice cold chamber. Samples were cultured by short term lymphocyte culture technique within 24 hours as given by Moorehead et al., (1960). At least 10 good quality metaphase spreads were considered to minimize sampling errors. The individual chromosomes were identified and classified as per the International System for the Cytogenetic Nomenclature of Domestic Animals (ISCNDA, 1990). The homologous pairs of chromosomes were identified and karyotyped based on their size and structure using IKARYOS software. Karyotypes established from the photographs taken from several good metaphase spreads were used for measuring the length of chromosomes.

The mitotic drive was estimated as the percentage of number of cells in metaphase and number of lymphoblasts to the total number of lymphocytes proliferated, whereas the mitotic index was calculated as the percent number of cells in metaphase to the total lymphocytes proliferated. The relative length (RL) of the individual chromosome was the ratio of length of the chromosome to the total length of genome including X chromosome and multiplied by 100. The Arms Ratio was calculated as ratio of length of long arm (q) to the length of short arm (p), Centromeric Index was calculated as the ratio of length of short arm (p) to the total length of chromosome (p+q) and multiplied by 100 and the Morphological Index was calculated by dividing the total length of chromosome (p+q) by the arms ratio and multiplied by 100. Idiogram was constructed by taking the chromosome number on X-axis and mean relative lengths of individual pairs of chromosomes on the Y- axis (Fig 3).

Mitotic drive and mitotic index
 
The mean mitotic drive in this study was found to be 64.5±2.01 per cent in bucks and 63.15±1.30 per cent in does of Nandidurga goats. Similar results (64.96%) were observed in local goats of Karnataka by Jayshree et al., (2014) and Kasabe et al., (2009) reported mean mitotic drive of 51.22±0.65 per cent in Berari does and 47.94±0.94 per cent in Berari bucks. The mitotic index in this study was found to be 13.25±1.00 in Nandidurga bucks and 12.7±1.08 per cent in Nandidurga does. Similar result (10.62%) was observed in local goats of Karnataka by Jayshree et al., (2014) and Kasabe et al., (2009) reported mean mitotic index was 6.59±0.58 per cent in Berari does and 5.29±0.85 per cent Berari bucks.
 
Number and morphology of chromosomes
 
The examination of all the metaphase spreads revealed a diploid number (2n) of 60 chromosomes with 58 autosomes and 2 sex chromosomes (XY in males and XX in females) (Fig 1 and Fig 2). All the autosomes were found to be acrocentric, X-chromosome was observed to be the longest acrocentric and the Y-chromosome was sub metacentric, which was confirmed by various indices (Arms Ratio, Centromeric Index and Morphological Index). Similar findings with regard to number and morphology of autosomes were reported in many Indian goat breeds like Kanniadu (Saravanan et al., 2006), Berari (Kasabe et al., 2009), Mahabubnagar (Ekambaram et al., 2011), Karnataka local goats (Jayashree, 2014), Sangamneri (Bhagat et al., 2014), Osmanabadi and Boer bucks (Kokani et al., 2018) and in native Black Bengal goats (Banani et al., 2018). In contradiction to the present findings, the autosomes were reported as telocentric in Tehran goats (Khavary, 1973), Korean local goats (Yeo, 1984) and in Ganjam and Black Bengal goats (Pattnayak and Patro, 1986).
 

 

 
The acrocentric nature of X-chromosome in the present study was in agreement with the reports for Korean native goats (Yeo, 1984), Berari (Kasabe et al., 2009), Mahabubnagar (Umadevi et al., 2011), Karnataka local goats (Jayashree, 2014), Sangamneri (Bhagat et al., 2014), Osmanabadi and Boer bucks (Kokani et al., 2018) and Native Black Bengal goats (Banani et al., 2018). In contradiction to the present finding, X-chromosome was reported to be telocentric in Tehran goats (Khavary, 1973). In the present study, Y-chromosome was found to be sub metacentric, however it was metacentric in morphology and smallest in the complement as reported by Khavary (1973), Ford et al., (1980), Jayashree (2014) in Karnataka local goats and Bhagat et al., (2014) in Sangamneri goats. Umadevi et al., (2011) reported that the Y chromosome appears to be smallest and dot like in Mahabubnagar local and in Black Bengal goats, respectively. Likewise, in Osmanabadi and Boer bucks, Y chromosome was the smallest dot like in majority of the metaphase examined and in few metaphases it was found to be sub metacentric in morphology (Kokani et al., 2018). In Black Bengal goats, Y-chromosome was found to be smallest, dot like structure and suspected to be sub-metacentric (Banani et al., 2018).
 
Relative length
 
In the present study, the mean relative length of autosomes varied from 2.08±0.24 to 4.81±0.12per cent in does and 2.09±0.09 to4.70±0.11 per cent to in bucks (Table 1). Analysis of relative length data revealed a non significant difference in the mean relative length of the chromosomes between the sexes. The mean relative lengths of autosomes ranged from 1.61 to 5.49 per cent in Kanniadu goats (Saravanan et al., 2006). The least square means for relative length of autosomes in unicolored, bicolored and multicolored Mahabubnagar goats ranged from 1.997 to 4.742, 2.050 to 5.065 and 2.041 to 4.672 per cent, respectively with no significant difference between them (Umadevi et al., 2011). The mean relative length (%) of autosomes varied from 1.65±0.11 to 5.69±0.18 in males and 1.68±0.13 to 5.26±0.16 in females and significant differences in relative length was observed between the sexes in 1^st, 16^th, 17^th, 19^th, 20^th, 21^st , 23^rd , 24^th and 25^th pair of autosomes (Jayashree, 2014). The relative length of autosomes varied from 1.79 to 5.19 per cent in females and in males from 1.78 to 5.25 per cent in Black Bengal goats (Banani et al., 2018).
 

 
In this study, the relative length of X- chromosome in Nandidurga does was 5.14±0.17 per cent and that in bucks was 4.92±0.21 per cent. It was reported as 5.1 to 5.8 per cent in Ganjam goats (Pattnanayak and Patre, 1986), 5.86±0.08 per cent (Ekambaram et al., 2011) and 5.16 per cent (Umadevi et al., 2011) in Mahbubnagar goats, 6.05±0.15 per cent in does and 6.28±0.31 per cent in bucks of local goats of Karnataka (Jayashree, 2014), 5.95±0.05 per cent in bucks and 5.57±0.05 per cent in does of Black Bengal goats (Banani et al., 2018). In the present study, Y- chromosome had a relative length of 1.99±0.20 per cent. The relative length Y chromosome was 1.36±0.05 per cent in Mehabubnagar goats (Ekambaram et al., 2011), 1.42±0.13 percent in local goats of Karnataka (Jayashree, 2014) and 1.47±0.03 percent in Black Bengal goats (Banani et al., 2018). Umadevi et al., (2011) reported as 1.96 per cent in Mahbubnagar goats.
 
The mean arms ratio of Nandidurga goats in the present investigation was 2.47 and arms ratio of all Y-chromosomes was found to be more than 1 and lesser than 7, mean centromeric index was 31.62 and centromeric index of all Y chromosomes was found to be more than 12.5 and lesser than 50.0 and average morphological index of Y-chromosome was 396.14 which was lesser than themean genome length of 812.4. All these indices confirm the sub metacentric nature of Y chromosome in the studied goats. However, Umadevi et al., (2011) reported arms ratio as 1.68 per cent (1.08 to 4.19), centromeric index as 39.22 percent, morphological index as 214.00 and genome length as 321.75 mm in Mahabubnagar goats. Idiogram was constructed by taking the chromosome number on X-axis and mean relative lengths of individual pairs of chromosomes on the Y- axis (Fig 3).
 

The present cytogenetic profiling of Nandidurga goats revealed chromosomal compliment which evinces the absence of any chromosomal abnormalities. This normal chromosome compliment reveals the status of Nandidurga goats for reproductive health and fertility, will benefit in enhancing production potentialities.