Portland State University. Department of Biology
Lester J. Newman
Date of Publication
Master of Science (M.S.) in Biology
Mosaicism, Down syndrome
1 online resource (116 p.)
Down Syndrome is a human condition caused by an extra copy of a #21 chromosome. At least one to two percent of free (not translocated) trisomy 21 cases are mosaics, i.e., they have two or more distinct cell lines. Usually, one cell line is 47 ,XX or XY ,+21 while the other cell line is normal 46,XX or 46,XY.
The purpose of the study was to establish the etiologies of the separate cell lines by determining whether the zygote was trisomic or normal. Meiotic non-disjunction in the formation of a gamete could lead to a trisomic zygote; loss of a #21 chromosome during a later mitotic division could then lead to a chromosomally normal cell line. Alternatively, a mitotic error in a normal embryo can produce a trisomy 21 cell line.
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Waggoner, Diane Dusenbery, "Origin of human trisomy 21 mosaicism" (1983). Dissertations and Theses. Paper 3402.