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Down syndrome: genetic recombination and the origin of the extra chromosome 21
Author(s) -
Hassold Terry,
Sherman Stephanie
Publication year - 2000
Publication title -
clinical genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 102
eISSN - 1399-0004
pISSN - 0009-9163
DOI - 10.1034/j.1399-0004.2000.570201.x
Subject(s) - nondisjunction , bivalent (engine) , meiosis , genetics , trisomy , biology , chromosome 21 , chromosome , prophase , chromosome segregation , aneuploidy , gene , chemistry , organic chemistry , metal
Despite the clinical importance of trisomy 21, we have been ignorant of the causes of meiotic nondisjunction of chromosome 21. Recently, however, genetic mapping studies of trisomy 21 families have led to the identification of the first molecular correlate of human nondisjunction; i.e. altered levels and positioning of meiotic recombinational events. Specifically, increases in 0 exchange events or in distal‐only or pericentromeric exchanges are significantly increased in trisomy 21‐generating meioses. These observations have led to the idea that chromosome 21 nondisjunction requires ‘two hits’: first, the establishment in prophase I of a ‘vulnerable’ bivalent and second, abnormal processing of the bivalent at metaphase I or II.