Miyashita N, Langley C H
Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Genetics. 1988 Sep;120(1):199-212. doi: 10.1093/genetics/120.1.199.
Restriction site and insertion/deletion polymorphism in a 45-kb region of the white locus on the X chromosome in Drosophila melanogaster was investigated for 64 X chromosome lines with six 6-cutter and ten 4-cutter restriction enzymes. A total of 109 polymorphisms were detected (54 restriction sites and 55 insertions/deletions). Estimated heterozygosity per nucleotide for this region (0.004-0.008) was similar to those of the Adh and 87A heat-shock locus regions located on the autosomes in D. melanogaster. This is contrary to a simple prediction based on the theory of mutation selection-balance of partially recessive deleterious mutants which predicts less variation on X chromosomes. Large linkage disequilibria between pairs of polymorphisms (including insertions and deletions) within the transcriptional unit (especially the 3' end of the 1st intron) were observed. As expected from population genetics theory, linkage disequilibria between these polymorphisms were greater for those pairs that are physically closer on the restriction map. Linkage equilibrium was typically observed when the pairs of sites were separated by 2 kb or more. Although significant between-line variation in eye pigment was observed (P less than 0.05), there is little evidence for strong associations between this phenotype and the polymorphisms at the DNA level.
利用六种六切点和十种四切点限制性内切酶,对64条X染色体品系黑腹果蝇X染色体上白色基因座45kb区域的限制性酶切位点及插入/缺失多态性进行了研究。共检测到109个多态性位点(54个限制性酶切位点和55个插入/缺失位点)。该区域每个核苷酸的估计杂合度(0.004 - 0.008)与黑腹果蝇常染色体上的乙醇脱氢酶基因座和87A热休克基因座区域的杂合度相似。这与基于部分隐性有害突变体的突变选择平衡理论的简单预测相反,该理论预测X染色体上的变异较少。在转录单位内(尤其是第一内含子的3'端),观察到多态性位点对之间(包括插入和缺失)存在较大的连锁不平衡。正如群体遗传学理论所预期的,在限制性图谱上物理距离更近的那些位点对之间,这些多态性位点的连锁不平衡更大。当位点对之间的距离相隔2kb或更多时,通常观察到连锁平衡。尽管观察到品系间眼色素存在显著差异(P小于0.05),但几乎没有证据表明这种表型与DNA水平上的多态性之间存在强关联。