Hofker M H, Smith S, Nakamura Y, Teshima I, White R, Cox D W
Research Institute, Hospital For Sick Children, Toronto, Ontario, Canada.
Genomics. 1990 Jan;6(1):33-8. doi: 10.1016/0888-7543(90)90445-z.
The genetic linkage map of chromosome 14q32 contains 11 loci which span a distance of more than 60 cM. We have assigned 10 of these loci and the AKT1 proto-oncogene to segments of 14q32, using breakpoints derived from four independent chromosomal deletions or rearrangements. The most telomeric breakpoint was found in a proband (HSC 6) carrying a ring-14 chromosome. HSC 6 is monosomic for the distal part of 14q32, which contains the immunoglobulin heavy-chain locus (IGH), and random markers D14S20, D14S19, and D14S23. Two other chromosomal breakpoints, found in probands HSC 121 and HSC 981, could not be distinguished from each other using DNA probes, although the cytogenetic breakpoints appeared to be different at 14q32.32 and 14q32.31, respectively. The region between the breakpoints of HSC 6 and HSC 121 contains AKT1, D14S1, D14S17, and D14S16. The entire telomeric band 14q32 is assumed to contain about 10% of chromosome 14, or approximately 10 Mb. The 8 most telomeric loci, including D14S1, map to 14q32.32-qter, which measures only several megabases. However, these loci span a genetic distance of 23 cM. The high recombination frequency contrasts with the observation that two of the gamma genes in the IGH constant region show a high degree of linkage disequilibrium, though 180 kb apart. This finding suggests that a telomeric localization per se does not lead to a higher recombination frequency and favors the hypothesis that the higher recombination frequency at the telomeres may be due to specific "hot spots" for recombination.
14号染色体长臂32区的遗传连锁图谱包含11个基因座，跨越距离超过60厘摩。我们利用源自四个独立染色体缺失或重排的断点，将其中10个基因座和AKT1原癌基因定位到14q32的各个区段。最末端的断点出现在一名携带14号环状染色体的先证者（HSC 6）中。HSC 6在14q32的远端部分为单体，该部分包含免疫球蛋白重链基因座（IGH）以及随机标记D14S20、D14S19和D14S23。在先证者HSC 121和HSC 981中发现的另外两个染色体断点，尽管细胞遗传学断点在14q32.32和14q32.31处似乎不同，但使用DNA探针无法区分彼此。HSC 6和HSC 121断点之间的区域包含AKT1、D14S1、D14S17和D14S16。整个14q32末端带被认为包含约10%的14号染色体，即大约10兆碱基。包括D14S1在内的最末端的8个基因座定位于14q32.32 - qter，其长度仅为几兆碱基。然而，这些基因座跨越的遗传距离为23厘摩。这种高重组频率与IGH恒定区的两个γ基因尽管相隔180千碱基却显示出高度连锁不平衡的观察结果形成对比。这一发现表明，末端定位本身并不会导致更高的重组频率，支持了端粒处较高重组频率可能归因于特定“重组热点”的假说。
