Euchromatic Variants
A class of variants that does not fit in with the usual perception of heteromorphism involves the so-called “euchromatic variants”, regions that are C-band negative and not generally anticipated to be variable in size or staining because they presumably c
- PDF / 80,274 Bytes
- 5 Pages / 439.37 x 666.142 pts Page_size
- 4 Downloads / 196 Views
Euchromatic Variants
5.1
Introduction
A class of variants that does not fit in with the usual perception of heteromorphism involves the so-called “euchromatic variants”, regions that are C-band negative and not generally anticipated to be variable in size or staining because they presumably contain genetic material. Euchromatic variants have become increasingly important at the molecular level, where deletions and duplications occur as normal variants throughout the genome (see Chap. 10). However, examples of such variants which are detectable at the microscope level are rare and are certainly appropriate subjects for critical scrutiny when they are observed. Euchromatic duplications and deletions (Table 5.1, originally compiled by Jalal and Ketterling) [1] included both light (G-negative) and dark (G-positive) bands identified by G-banding that seemed to be phenotypically neutral. They emphasized that all euchromatic duplications and deletions should be interpreted with caution. In order for a euchromatic deletion or duplication to be regarded as a normal variant, they indicated the following criteria should be met. It should have been: 1. 2. 3. 4.
Reported in a relatively large number of individuals Passed on from parents to children Associated with a normal phenotype The identity of the extra or missing chromatin confirmed by chromosome banding and/or molecular/molecular cytogenetic procedures.
Emphasized for euchromatic duplications, was the necessity to rule out moderately or highly repetitive DNA sequences that are C-band negative, such as alpha satellite, satellite III and ribosomal DNA. There is evidence fpr the presence and amplification of pseudogene cassettes in 16p11.2, which included pseudogenes for immunoglobulin heavy chain from 14q32, myosin heavy chain from Xq28, and
© Springer Nature Singapore Pte Ltd. 2017 H.E. Wyandt et al., Human Chromosome Variation: Heteromorphism, Polymorphism and Pathogenesis, DOI 10.1007/978-981-10-3035-2_5
57
58 Table 5.1 Euchromatic variants (adapted from Jalal and Ketterling [1])
5 Euchromatic Variants Chr
Duplications
1
1p21-p31 1q42,11-q4212
2 3 4 5
Deletions
2q14.1 3p25.3 4q35 5p14 5q15-q21
6 8
6q23.1-q24.2 8p23.1 8q24.13-q24.22
9 11 13 15 16
9p12? 9q13-q21 11p12 13q21 15q12.2-q13.1 16p11.1-p12 16q21
18 X
18p+ Xq26
Reference(s) [2] [3] [4] [5] Fig. 6.10d [6–9] [10] [11–13] [14–16] [17–19] [20] [21–23] [24] [25] [26–34] [35–39] [6, 40–43] [44–49] [50]
minisatellite sequences from the telomeric region of 6p [51]. There are also reports of paralogous segments of Xq28 found near the centromeres of chromosomes 2p, 10p, 16p and 22q [52, 53]. It has since has become increasing evident that micro-duplications, deletions and amplifications involving microsatellites and pseudogenes occur throughout the genome and that such sequences at telomeric, centromeric, neocentromeric, and interstitial fragile sites have significant roles in chromosome rearrangements, in gene expression and in chromosome evolution. The characterization of unusual variants with greater p
Data Loading...
