Only in rare cases of a mosaicismthe presence of a normal cell line, in addition to the trisomic cell line, may support the development of a viable trisomy of the other chromosomes. Surveys of cases of human aneuploidy syndromes have shown that most of them are maternally derived.
Nondisjunction during mitosis leads to one daughter receiving both sister chromatids of the affected chromosome while the other gets none. Analysis of chromosomal distribution in unbalanced cells demonstrated that both X homologues were frequently involved.
Formally, X chromosome monosomy Turner syndromesee above can also be classified as a form of sex chromosome aneuploidy. The term sex chromosome aneuploidy summarizes conditions with an abnormal number of sex chromosomes, i.
Normal MI A, B. One of the donors was a smoker case 1 and none of them had been exposed to known mutagens or radiation. Simon ThomasN. Celia de Lozier-Blanchet. Lisbeth Tranebjaerg. Journal of Proteome Research. In MI, sex chromosomes had one chiasma in Mitotic nondisjunction results in somatic mosaicismsince only daughter cells originating from the cell where the nondisjunction event has occurred will have an abnormal number of chromosomes.
These cells, which are thought to arise from parental monosomic and trisomic types, may indicate the malsegregation of X chromosomes in vivo. The only known survivable monosomy in humans is Turner syndromewhere the affected individual is monosomic for the X chromosome see below.
Ballard, Christine A. New York: Garland Science.
Sex-Linked Inheritance in Drosophila. As a consequence, the organism evolves as a mixture of cell lines with differing ploidy number of chromosomes. PLOS Genetics.