性染色体：遗传学、异常和疾病

English | ISBN: 1607413043 | 2009 | 279 pages | PDF | 17 MB

Sex chromosomes determine the sex of an organism. A human somatic cell has two sex chromosomes: XY in male and XX in female. A human germ cell has one sex chromosome: X or Y in a sperm and X in an egg. When an X-sperm is combined with an egg, the resulting zygote (fertilised egg) will contain two X chromosomes. A person developed from the XX-zygote will have the characteristics of a female. Combination of a Y-sperm and an egg will produce a male. Usually, a woman has two X chromosomes (XX) and a man one X and one Y (XY). However, both male and female characteristics can sometimes be found in one individual, and it is possible to have XY women and XX men. Analysis of such individuals has revealed some of the molecules involved in sex determination, including one called SRY, which is important for testis formation. SRY (which stands for sex-determining region Y gene) is found on the Y chromosome. In the cell, it binds to other DNA and in doing so distorts it dramatically out of shape. This alters the properties of the DNA and likely alters the expression of a number of genes, leading to testis formation. Most XX men who lack a Y chromosome do still have a copy of the SRY gene on one of their X chromosomes (moved there by chromosomal translocation). This copy accounts for their maleness. However, because the remainder of the Y chromosome is missing they frequently do not develop secondary sexual characteristics in the usual way. This book presents the latest research in the field from around the world.

性染色体决定了生物的性别。一个人的体细胞有两条性染色体：雄性的XY和雌性的XX。人的生殖细胞有一条性染色体：精子中一条X或Y，卵子中一条X。当携带X精子结合卵子时，形成的合子（受精卵）将包含两条X性染色体。从XX-合子发育而成的人会表现出女性特征。一个Y精子与卵子结合则会产生雄性。通常情况下，女人有两个X性染色体（XX），男人有一个X和一个Y（XY）。然而，在某些个体身上男性和女性的特征有时都会存在，也可以发现XY的女性和XX的男性。对这些个体的研究揭示了一些参与性别决定的分子，包括一种名为SRY的基因，它在睾丸形成中起重要作用。SRY（sex-determining region Y gene）位于Y染色体上，在细胞内它会与DNA结合，并且严重扭曲了DNA形状。这改变了DNA的性质并可能导致许多基因表达的变化，进而导致睾丸的形成。大多数缺少Y性染色体的XX雄性个体仍然在其一个X性染色体上拥有SRY基因（通过染色体易位转移到那里）。这个拷贝解释了他们的男性特征。然而因为剩余的部分Y性染色体缺失了，他们经常不会按照正常方式发展出第二性征。本书介绍了全球范围内该领域的最新研究结果。

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