脆弱的X重复的神秘和极性变异可能会导致正常等位基因的倾向
1Howard Hughes Medical Institute, Emory University School of Medicine, Atlanta, Georgia 30322.
Cell
|June 17, 1994
概括
脆弱X综合征是由CGG重复扩张引起的. 某些具有较长CGG重复的正常基因变异 (半型) 可能会使个体容易患上这种疾病,这表明正在进行的遗传进化.
科学领域:
- 遗传学 是一个遗传学.
- 分子生物学分子生物学
- 人类疾病 人类疾病
背景情况:
- 脆弱X综合征是由FMR1基因中CGG重复扩张引起的.
- 正常的等位基因含有AGG中断,但存在变异.
- 连接不平衡表明正常单双类型对脆弱的X染色体的贡献不平等.
研究的目的:
- 为了研究CGG在正常等位基内重复的单位基型特异性变异.
- 识别可能导致脆弱X综合征的潜在祖先等位基因.
- 为了探索FMR1位点的进化动态.
主要方法:
- 正常FMR1等位基因的序列分析.
- 哈普洛型分析以评估链接不平衡.
- 检查CGG重复长度和AGG中断模式.
主要成果:
- 观察到CGG重复结构的哈普洛型特异变异,特别是在3'端.
- 具有>24个完美的3'CGG重复的正常基因基因在过度代表的单元型中更为常见.
- 这些特定的等位基因,在正常染色体的2%中发现,可能代表脆弱的X扩张的祖先池.
结论:
- CGG重复稳定性的变化可能与DNA复制链偏差有关.
- 某些具有扩展完美的CGG重复的正常基因可能是脆弱的X扩张的祖先前体.
- FMR1位点可能正在经历持续的进化变化,并处于不稳定的平衡状态.
相关概念视频
Genetic Lingo
Overview
Pedigree Analysis
Overview
X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
Sex-linked Disorders
Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.
Position-effect Variegation
In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
X-linked Traits
In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.


