Millot P, Chatelain J, Dautheville C, Salmon D, Cathala F
Institut Pasteur, Paris, France.
Immunogenetics. 1988;27(1):1-11. doi: 10.1007/BF00404437.
As seen on their family trees, Ile-de-France sheep with scrapie show genetic susceptibility to this disease, which is transmitted via scrs, an autosomal recessive gene. Scrapie occurred in homozygous recessive sheep, whereas the presence of the dominant resistance allele Scrr sufficed to prevent this disease in heterozygous animals. This hypothesis, previously proposed by Parry (1962), was tested in a study involving 133 crossings of sheep of different genotypes, and verified in the observed progenies. In a contaminated environment, susceptibility to the disease seemed to be transmitted by the scrs gene, whose frequency was increasing and varied in different progenies: the gene was propagated by inbreeding combined with selection; scrapie did not appear in the progeny of a homozygous resistant ram with the Scrr/Scrr genotype. On the family trees, linkage between the Scr locus and the OLA-A and -B loci is clearly visible; it often allowed the transmission of resistance or susceptibility haplotypes to be detected by OLA typing and followed from one generation to the next. The Scrr, OLA-A4, B6 haplotype was not found in any diseased sheep born before 1979, but was propagated by healthy sheep. During and after 1979, several recombinations of this haplotype were observed, giving a recombined haplotype with reciprocal linkage (scrs, OLA-A4, B6), disseminated by one sire in particular. The rate of recombination of Scr and OLA loci is estimated to be between 11 and 16%. The possibility of early selection against the disease without loss of qualities desired by the breeder is discussed.
从它们的系谱可以看出，患有羊瘙痒病的法兰西岛绵羊对这种疾病表现出遗传易感性，这种疾病是通过scrs（一种常染色体隐性基因）传播的。羊瘙痒病发生在纯合隐性绵羊中，而显性抗性等位基因Scrr的存在足以在杂合动物中预防这种疾病。这个先前由帕里（1962年）提出的假设，在一项涉及133次不同基因型绵羊杂交的研究中得到了检验，并在观察到的后代中得到了验证。在受污染的环境中，对这种疾病的易感性似乎是由scrs基因传播的，其频率在增加且在不同后代中有所不同：该基因通过近亲繁殖与选择相结合而传播；具有Scrr/Scrr基因型的纯合抗性公羊的后代中没有出现羊瘙痒病。在系谱上，Scr基因座与OLA - A和 - B基因座之间的连锁关系清晰可见；它常常使得通过OLA分型检测抗性或易感性单倍型的传递并追踪到下一代成为可能。Scrr、OLA - A4、B6单倍型在1979年之前出生的任何患病绵羊中都未发现，但由健康绵羊进行了传播。在1979年期间及之后，观察到了这种单倍型的几次重组，产生了一种具有反向连锁的重组单倍型（scrs、OLA - A4、B6），特别是由一头种公羊传播开来。Scr和OLA基因座的重组率估计在11%至16%之间。文中讨论了在不损失育种者所期望品质的情况下早期选择对抗该疾病的可能性。
