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Besides the centromere, one or more secondary constrictions can also be observed in some chromosomes at metaphase. The secondary constrictions are always constant in their positions and hence can be used as markers that identify particular chromosomes. A satellite chromosome or SAT chromosome has a chromosome segment that is separated from the main body of the chromosome by such a secondary constriction. The term is due to Sergei Navashin, in 1912. The satellite at metaphase appears to be attached to the rest of the body of chromosomes by a thread of chromatin. If the secondary constriction contains the nucleolus organizer region, the chromosome is called a nucleolar satellite chromosome.〔 There are at least 2 SAT chromosomes in each diploid nucleus. They play a vital role in the formation of the nucleolus after cell division is completed. In humans, chromosomes number 13, 14, 15, 21 and 22 are examples of SAT chromosomes. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Satellite chromosome」の詳細全文を読む スポンサード リンク
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