Imprinting and X-Chromosome Inactivation

摘要: In normal female mammals one of the two X-chromosomes in every somatic cell is inactive i.e. it fails to transcribe RNA (reviews Gartler et al. 1992; Migeon 1994; Lyon 1996). The result this that chromosomally XX females and XY males both effectively have a single dosage products X-linked genes. Thus X-chromosome inactivation fulfils function compensation eutherian mammals, typically either any cell, maternally inherited Xm or paternally Xp, can be inactivated at random. Once choice made each remains stable all further generations individual hence adult there are large clumps cells with same active. If bear different alleles gene affecting some visible character, such as coat color, seen variegated effect. best-known example tortoiseshell cat, which pattern results from animal having for ginger on black tabby other. However, by contrast, marsupials X-chromosome, derived becomes (Cooper 1993; Graves This preferential Xp also extraembryonic lineages embryo, give rise placenta other supporting tissues, mice rats (Takagi Sasaki 1975), probably, but less clearly, humans (Harrison 1989; Goto 1997). Thus, tissues eutherians, shows imprinting (Fig. 1). has similarities differences autosomal imprinting. order understand significance must consider mechanism brought about.