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Centrometric linkage in autosomal trisomies

Centrometric linkage in autosomal trisomies BY G. B. C8TB* AND J. H. EDWARDS The Infant Development Unit, Birmingham Maternity Hospital, Queen Elizabeth Medical Centre, Birmingham B15 BTG, England Trisomies provide an additional way of observing the segregation of chromosomes and of the loci they carry. Apart from causing a specific syndrome, the extra chromosome should predictably affect the segregation pattern of the phenotypes defined a t the loci it carries. Analysis of its effects and the detection of linkage depend on a n understanding of the cytological mechanisms involved. In the model presented below, asynapsis, the non-pairing of two homologous chromosomes a t meiosis, is implied, and considered together with cases of non-disjunction at the first meiotic division. Let us consider two homologous chromosomes associated in a tetrad of four chromatids at the diplotene stage of meiosis (Fig. 1). If a cross-over occurs between a locus and its centromere, two of the four chromatids are recombinants, and two are non-recombinants (Fig. 2). Providing the chromatids are involved a t random, the average result will be the same for any number of cross-overs and there will be an equal number of apparent recombinant and non-recombinant chromatids (Fig. 3). We will use the word ‘chromatid’ http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Annals of Human Genetics Wiley

Centrometric linkage in autosomal trisomies

Annals of Human Genetics , Volume 39 (1) – Jul 1, 1975

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References (6)

Publisher
Wiley
Copyright
Copyright © 1975 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0003-4800
eISSN
1469-1809
DOI
10.1111/j.1469-1809.1975.tb00107.x
Publisher site
See Article on Publisher Site

Abstract

BY G. B. C8TB* AND J. H. EDWARDS The Infant Development Unit, Birmingham Maternity Hospital, Queen Elizabeth Medical Centre, Birmingham B15 BTG, England Trisomies provide an additional way of observing the segregation of chromosomes and of the loci they carry. Apart from causing a specific syndrome, the extra chromosome should predictably affect the segregation pattern of the phenotypes defined a t the loci it carries. Analysis of its effects and the detection of linkage depend on a n understanding of the cytological mechanisms involved. In the model presented below, asynapsis, the non-pairing of two homologous chromosomes a t meiosis, is implied, and considered together with cases of non-disjunction at the first meiotic division. Let us consider two homologous chromosomes associated in a tetrad of four chromatids at the diplotene stage of meiosis (Fig. 1). If a cross-over occurs between a locus and its centromere, two of the four chromatids are recombinants, and two are non-recombinants (Fig. 2). Providing the chromatids are involved a t random, the average result will be the same for any number of cross-overs and there will be an equal number of apparent recombinant and non-recombinant chromatids (Fig. 3). We will use the word ‘chromatid’

Journal

Annals of Human GeneticsWiley

Published: Jul 1, 1975

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