Notter D R, Cockett N E, Hadfield T S
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Anim Sci. 2003 Apr;81(4):912-7. doi: 10.2527/2003.814912x.
The effect of the melatonin receptor 1a (MTNR1A) gene on fertility and litter size in autumn lambing was studied with 373 ewes from a population of sheep selected for 10 yr for fertility in May and June matings. Animals were from a composite line of 50% Dorset, 25% Rambouillet, and 25% Finnsheep. Two restriction fragment length polymorphisms were present in the population, with allelic frequencies of 0.42 and 0.58 for an MnII polymorphism (alleles M and m, respectively) and of 0.34 and 0.66 for an RsaI polymorphism (alleles R and r, respectively). Genotypic frequencies for the polymorphisms were not independent, suggesting an association between them in foundation animals. Effects of MTNR1A genotype on fertility and litter size were evaluated using mixed linear model or REML procedures, but were not significant for matings involving ewes of all ages. However, in adult ewes (3 yr old and older), fertility of ewes of genotype mm was 10.0 (mixed model; P < 0.09) to 11.2% (REML; P = 0.03) less than that of other ewes. Genotypic effects associated with MTNR1A in adult ewes accounted for 23.8% of the estimated total additive genetic variance in fertility. Litter size was not significantly associated with MTNR1A genotype; adult ewes of genotype mm had approximately 0.11 fewer lambs per ewe lambing than ewes of other genotypes. Fertility in autumn lambing is lowly heritable, expressed only in females, and manifested relatively late in life and only in some management systems. Access to genetic markers would thus be advantageous in selection programs.
利用来自一个经过10年选育的绵羊群体的373只母羊，研究了褪黑素受体1a（MTNR1A）基因对秋季产羔时繁殖力和产羔数的影响。该群体用于5月和6月配种时的繁殖力选育。这些动物来自一个复合品系，其中50%为多塞特羊、25%为兰布列羊和25%为芬兰羊。该群体中存在两种限制性片段长度多态性，MnII多态性（等位基因分别为M和m）的等位基因频率为0.42和0.58，RsaI多态性（等位基因分别为R和r）的等位基因频率为0.34和0.66。这两种多态性的基因型频率并非相互独立，表明在基础动物中它们之间存在关联。使用混合线性模型或REML程序评估了MTNR1A基因型对繁殖力和产羔数的影响，但对于涉及所有年龄母羊的配种，这些影响并不显著。然而，在成年母羊（3岁及以上）中，基因型为mm的母羊的繁殖力比其他母羊低10.0%（混合模型；P < 0.09）至11.2%（REML；P = 0.03）。成年母羊中与MTNR1A相关的基因型效应占繁殖力估计总加性遗传方差的23.8%。产羔数与MTNR1A基因型无显著关联；基因型为mm的成年母羊每产羔一只母羊所产的羔羊数比其他基因型的母羊少约0.11只。秋季产羔时的繁殖力遗传力较低，仅在雌性中表现，且在生命后期相对较晚表现，并且仅在某些管理系统中表现。因此，获取遗传标记在选择计划中具有优势。
