因为产妇年龄过大,卵细胞可发生变化,人体包括卵巢所承受的各种射线和有害物质的影响也就越多,这些因素都会使遗传物质发生突变的机会增多,遗传物质染色体在细胞分裂过程中发生不分离现象,最常见的是21号染色体不分离,结果出现先天性愚型儿。患儿的染色体分析检查可见有3条21号染色体,故又称“21—三体综合征”。这 Because maternal age is too large, egg cells can change, the human body, including the ovaries are exposed to a variety of rays and harmful substances also have more influence, these factors will increase the chances of genetic material mutation, genetic material chromosomes in the cell division process Non-separation occurs, the most common is the chromosome 21 does not separate, resulting in congenital stupid children. Children’s chromosome analysis showed that there are three chromosome 21, it is also known as “21-trisomy syndrome.” This