Human Molecular Genetics, Vol 7, 2113-2120, Copyright © 1998 by Oxford University Press
R Andreassen and B Olaisen
We have studied the allelic diversity and de novo mutations at the
hypervariable minisatellite locus D7S22. A four-state minisatellite variant
repeat unit mapping by PCR (MVR-PCR) method was developed for this purpose,
and a substitution polymorphism close to the repeat array was used to
design allele-specific flanking primers to study individual haplotypes in
genomic DNA. A total of 150 alleles from different allele size groups and
flanking haplotypes were mapped. On average, MVR-codes extending 65 repeats
(2.4 kb) into the repeat array were obtained. The interspersion patterns of
variant repeats were highly polymorphic. However, subgroups of alleles
close in size and with identical flanking haplotype revealed common
MVR-code characteristics indicating a close evolutionary relationship.
Unlike the situation in many other hypervariable minisatellites, no
polarized variability was revealed at this minisatellite locus. Fifty four
small families with D7S22 de novo mutations were analysed by MVR-PCR. The
sites where the length change occurred were revealed in 22 cases, while in
32 cases the mutation obviously occurred further into the repeat array. In
agreement with a non-polar distribution of the allelic variation, there was
no evidence for a hypermutable hot spot for mutation within the repeat
array. Comparison of MVR-codes in the mutant and progenitor in gain
mutations indicated that at least one, possibly four cases, reflected
inter- allelic events. Together with evidence from DNA sequencing of
alleles of <2 kb, this indicates that as many as half of the gain
mutations might be inter-allelic events in D7S22. Based on these results,
different factors which might affect the mutation rate are discussed.
ARTICLES
De novo mutations and allelic diversity at minisatellite locus D7S22 investigated by allele-specific four-state MVR-PCR analysis
Institute of Forensic Medicine, University of Oslo, Rikshospitalet 0027 Oslo, Norway. rune.andreassen@labmed.uio.no
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