T. Shixin and H. Jianlin
Laboratory of Animal Genetics, Department of Animal Science, Gansu Agricultural University, Lanzhou 730070, Gansu, P.R. China
Polyacrylamide gel electrophoresis was used to analyse haemoglobin (Hb) polymorphism in six yak populations (Jianza County of Qinghai Province, Sunan County, Tianzhu County, Maqu County, Luqu County and Xiahe County of Gansu Province), two cattle populations (Wuwei City and Linxia County of Gansu Province) and one F1 hybrid population (Linxia County). The results show that the Hb locus in yak consists of only one genotype (HbAA). At the opposite the Yellow cattle studied show three alleles (HbA, HbB and HbC), with three genotypes detected in the population from Linxia County (HbAA, HbBB, HbBC) and five genotypes detected in the population from Wuwei City (HbAA, HbAB, HbBB, HbBC and HbAC). The F1 hybrid population has three alleles (HbA, HbB and HbC) with three genotypes (HbAA, HbAB and HbAC). In cattle and in cattle × yak hybrid the commonest allele is HbA.
Keywords: Cattle, haemoglobin, hybrid, polymorphism, yak
As a unique domestic animal living in the high altitude zones, the yak (Bos grunniens) remain productive in the extreme environmental condition of the Qinghai-Tibetan Plateau where hardly any other livestock can survive. China is a main country on yak husbandry and it has more than 95% of the total yak population in the world.
Haemoglobin (Hb) is the major carrier of oxygen in the blood. Genetic variation at the protein might reflect adaptation to local environmental conditions. Ranchev (1981) and Nyamsamba and Zagdsuren (1994) identified three genotypes (HbAA, HbAB and HbBB) and two alleles (HbA and HbB) in Mongolian yak. However, no polymorphisms were identified in Tianzhu White yak, Nepalese yak, Jiulong yak, Tibetan yak and Maiwa yak (Men et al. 1989; Qi et al. 1991; Namikawa et al. 1992; Cheng et al. 1995; Zhong et al. 1999).
The purpose of this study is to extend these previous findings into a larger geographic area with the analysis of new yak populations. Also, we will compare genetic variation in yak's haemoglobin with the ones present in Yellow cattle and hybrids Yellow cattle × yak.
Samples of six yak populations were collected from Sunan County (n = 38), Tianzhu County (n = 63), Maqu County (n = 69), Xiahe County (n = 20), Luqu County of Gansu Province (n = 36), and Jianza County of Qinghai Province (n = 43). Two cattle populations, from Wuwei city (n = 46) and Linxia County of Gansu (n = 22), and one F1 hybrid population from Linxia (n = 45) were also analysed.
Gel electrophoresis conditions were in accordance to the findings of Han et al. (1996). After electrophoresis the gel was dyed using Commassie Brilliant Blue (G250) for about thirty minutes and then washed in 7% acetic acid solution. We used the standard nomenclature from Namikawa et al. (1992) for the calling of the Hb genotypes (Figure 1).
Source: Namikawa et al. (1992).
Figure 1. Possible haemoglobin genotypes.
In this study, we could not identify polymorphism at the Hb locus in 269 yak samples from six populations. Only the HbAA genotype was found in yak. At the opposite the two Yellow cattle populations were polymorphic at the Hb loci. We identified three alleles and four genotypes in the Linxia population, meanwhile the same alleles and five genotypes were present in the Wuwei population. The Hb loci of F1 hybrid population were also polymorphic with three alleles and three genotypes (Table 1). The allele and genotype frequencies in F1 (Yellow cattle × yak) is similar to the ones found by Namikawa et al. (1992) in the Nepalese hybrids of yak × cattle.
The absence of polymorphism at the haemoglobin locus in yak populations analysed in this study and previous works which failed to identify any polymorphism in all but one population of yak (Ranchev 1981; Men et al. 1989; Qi et al. 1991; Namikawa et al. 1992; Nyamsamba and Zagdsuren 1994; Cheng et al. 1995; Zhong et al. 1999) strongly support that genetically pure yak populations will be monomorphic at the haemoglobin locus for allele HbA. Also, it suggests that the HbAA genotype might have been selected in yak given its possible stronger affinity for oxygen. Therefore, Hb polymorphism present in Mongolian yak (Ranchev 1981; Nyamsamba and Zagdsuren 1994) show past hybridisation efforts in yak population.
Table 1. Allelic and genotypic frequencies observed at the haemoglobin locus.
Population |
No. of animal |
Allele frequencies |
Genotype frequencies | ||||||
A |
B |
C |
AA |
BB |
AB |
BC |
AC | ||
Wuwei cattle |
46 |
0.794 |
0.163 |
0.043 |
0.717 |
0.087 |
0.110 |
0.043 |
0.043 |
Linxia cattle |
22 |
0.909 |
0.068 |
0.023 |
0.910 |
0.045 |
– | 0.045 |
– |
F1 hybrids |
45 |
0.967 |
0.022 |
0.011 |
0.934 |
– | 0.044 |
– | 0.022 |
Yak |
269 |
1.000 |
– | – | 1.000 |
– | – | – | – |
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