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A J Jeffreys

Publications and source records attributed to A J Jeffreys.

At least 37 records · Page 2Linked to original sources
PubMed2000

Are DNA profiles breed-specific? A pilot study in pigs.

In this study, DNA fingerprints from 32 unrelated domestic pigs were analysed and screened for breed-specificity. Three breed groups were analysed: Chinese Meishan, Large White and a collection of other European breeds. Ninety-three distinct and variable bands were used to estimate genetic distances between the animals. Between the groups these individual genetic distances substantially exceeded those within a group. Linear discriminant analysis showed that the 23 most common DNA fragments revealed sufficient breed-specificity as to assign each pig correctly to its breed or breed group. These findings, although based on a small sample, indicate that selective use of minisatellite variation in pigs appears to be a valuable novel approach toward the development of breed DNA profiles and the resolution of breed relationships.

Animals↗
PubMed1999

Human minisatellites, repeat DNA instability and meiotic recombination.

Minisatellites include some of the most variable loci in the human genome and are superb for dissecting processes of tandem repeat DNA instability. Single DNA molecule analysis has revealed different mutation processes operating in the soma and germline. Low-level somatic instability results in simple intra-allelic rearrangements. In contrast, high frequency germline instability involves complex gene conversions and is therefore recombinational in nature, almost certainly occurring at meiosis. To determine whether true meiotic crossovers occur at human minisatellites, we have used polymorphisms near the repeat array to recover recombinant DNA molecules directly from sperm DNA. Analysis of minisatellite MS32 has revealed an intense and highly localised meiotic crossover hotspot centred upstream of the array, the first example of a human hotspot defined at the molecular level. This hotspot extends into the beginning of the repeat array, resulting in unequal and equal crossovers. Array crossovers occur much less frequently than array conversions but appear to arise by a common process, most likely by alternative processing of a recombination initiation complex. The location of MS32 at the boundary of a recombination hotspot suggests that this locus has evolved as a by-product of localised meiotic recombination activity, and that minisatellites might in general mark recombinationally proficient hotspots or hot domains in the genome. Finally, sperm crossover analysis makes it possible to explore the molecular rules that govern human meiotic recombination, and to detect phenomena such as meiotic drive that could provide a possible connection between recombination and DNA sequence diversity itself.

DNA↗
PubMed1999

Minisatellite instability and germline mutation.

Tandem-repeat DNA actively turns over in the genome by a variety of poorly understood dynamic mechanisms. Minisatellites, a class of tandem repeats, have been shown to cause disease by influencing gene expression, modifying coding sequences within genes or generating fragile sites. There has been recent rapid progress towards understanding molecular turnover processes at human minisatellites. Instability at GC-rich minisatellites appears to involve distinct mutation processes operating in somatic and germline cells. In the germline, complex conversion-like events occur, probably during meiosis. Repeat turnover appears to be controlled by intense recombinational activity in DNA flanking the repeat array, suggesting that minisatellites might evolve as by-products of localised meiotic recombination in the human genome. In contrast, AT-rich minisatellites appear to evolve by intra-allelic processes such as replication slippage. Curiously, minisatellites in other organisms appear to be more stable than their human counterparts, suggesting species-specific differences in turnover processes. Some yeast models display human-like minisatellite turnover processes at meiosis. However, all attempts to transfer human germline instability to transgenic mice have failed. Finally, tandem repeat instability in various species appears to be extremely sensitive to environmental agents such as radiation via a mechanism which remains enigmatic.

Animals↗
PubMed1999

DNA profiling reveals remarkably low genetic variability in a herd of SLA homozygous pigs.

Inbred strains of rodents have become indispensable for a wide range of biological studies. It has generally been accepted that genetic uniformity is unlikely to be achieved before 20 generations of brother x sister matings discouraging attempts to inbreed larger mammals. Nevertheless, pigs, homozygous for the swine MHC haplotype SLA b/b, have been inbred at the Babraham Institute for almost thirty years and used for immunological studies. Since the herd had not been studied at the DNA level, DNA profiling at multiple hypervariable loci was performed and surprisingly little genetic polymorphism and extremely high inter-individual resemblance were observed reminiscent of that observed in inbred strains of mice.

Animals↗
PubMed1999

Extremely complex repeat shuffling during germline mutation at human minisatellite B6.7.

Human minisatellite B6.7 is a highly variable locus showing extensive heterozygosity with alleles ranging from six to >500 repeat units. Paternal and maternal mutation rates to new length alleles were estimated from pedigrees at 7.0 and 3.9% per gamete, respectively, indicating that B6.7 is one of the most unstable minisatellites isolated to date. Mutation at this locus was also analysed by small pool PCR of sperm and blood DNA. Male germline instability varied from <0.8 to 14% per allele and increased with tandem array size. In contrast, the frequency of mutants in somatic (blood) DNA was far lower (<0.5%), consistent with a meiotic origin of germline mutants. Sperm mutants were further characterized by minisatellite variant repeat mapping using four major polymorphic sites within the B6.7 repeats. This highly informative system revealed a wide variety of changes in allele structure, including simple intra-allelic duplications and deletions and more complicated inter- and intra-allelic transfers of repeat blocks, as seen at other human minisatellites. The main mode of sperm mutation, however, resulted in extremely complex allele reorganization with evidence of inter-allelic transfer plus the generation of novel repeats by rearrangement at the sub-repeat level, suggesting that recombinational instability at B6.7 is a complex multistep process.

Alleles↗
PubMed1999

Comparative sequence analysis of human minisatellites showing meiotic repeat instability.

The highly variable human minisatellites MS32 (D1S8), MS31A (D7S21), and CEB1 (D2S90) all show recombination-based repeat instability restricted to the germline. Mutation usually results in polar interallelic conversion or occasionally in crossovers, which, at MS32 at least, extend into DNA flanking the repeat array, defining a localized recombination hotspot and suggesting that cis-acting elements in flanking DNA can influence repeat instability. Therefore, comparative sequence analysis was performed to search for common flanking elements associated with these unstable loci. All three minisatellites are located in GC-rich DNA abundant in dispersed and tandem repetitive elements. There were no significant sequence similarities between different loci upstream of the unstable end of the repeat array. Only one of the three loci showed clear evidence for putative coding sequences near the minisatellite. No consistent patterns of thermal stability or DNA secondary structure were shared by DNA flanking these loci. This work extends previous data on the genomic environment of minisatellites. In addition, this work suggests that recombinational activity is not controlled by primary or secondary characteristics of the DNA sequence flanking the repeat array and is not obviously associated with gene promoters as seen in yeast.

CpG Islands↗
PubMed1999

The potential contribution of MVR-PCR to paternity probabilities in a case lacking a mother.

Minisatellite variant repeat (MVR) mapping using the polymerase chain reaction (PCR) was applied to a paternity case lacking a mother to evaluate the paternity probability. After three flanking polymorphic sites at each of MS31A and MS32 loci were investigated from the child and alleged father, allele-specific MVR-PCR was performed using genomic DNA. It was confirmed that one allele in the child was identical to that in the alleged father at both loci. Mapped allele codes were compared with allele structures established from population surveys. No perfect matches were found although some motifs were shared with other Japanese alleles. The paternity index and probability of paternity exclusion at these two MVR loci were then estimated, establishing the power of MVR-PCR even in paternity cases lacking a mother.

Alleles↗
PubMed1998

Repeat instability at human minisatellites arising from meiotic recombination.

Little is known about the role of meiotic recombination processes such as unequal crossover in driving instability at tandem repeat DNA. Methods have therefore been developed to detect meiotic crossovers within two different GC-rich minisatellite repeat arrays in humans, both in families and in sperm DNA. Both loci normally mutate in the germline by complex conversion-like transfer of repeats between alleles. Analysis shows that inter-allelic unequal crossovers also occur at both loci, although at low frequency, to yield simple recombinant repeat arrays with exchange of flanking markers. Equal crossovers between aligned alleles, resulting in recombinant alleles but without change in repeat copy number, also occur in sperm at a similar frequency to unequal crossovers. Both crossover and conversion show polarity in the repeat array and are co-suppressed in an allele showing unusual germline stability. This provides evidence that minisatellite conversion and crossover arise by a common mechanism, perhaps by alternative processing of a meiotic recombination initiation complex, and implies that minisatellite instability is a by-product of meiotic recombination in repeat DNA. While minisatellite recombination is infrequent, crossover rates indicate that the unstable end of a human minisatellite can act as a recombination warm-spot, even between sequence-heterologous alleles.

Crossing Over, Genetic↗
PubMed1998

Isolation and characterization of mouse minisatellites.

Minisatellites provide the most informative system for analyzing processes of tandem repeat turnover in humans. However, little is known about minisatellites and the mechanisms by which they mutate in other species. To this end, we have isolated and characterized 76 endogenous mouse VNTRs. Fifty-one loci have been localized on mouse chromosomes and, unlike in humans, show no clustering in proterminal regions. Sequence analysis of 25 loci revealed the majority to be authentic minisatellites with GC-rich repeat units ranging from 14 to 47 bp in length. We have further characterized 3 of the most polymorphic loci both in Mus musculus subspecies and in inbred strains by using minisatellite variant repeat mapping (MVR) by PCR to gain insight into allelic diversity and turnover processes. MVR data suggest that mouse minisatellites mutate mainly by intra-allelic nonpolar events at a rate well below 10(-3) per gamete, in contrast to the high-frequency complex meiotic gene conversion-like events seen in humans. These results may indicate a fundamental difference in mechanisms of minisatellite mutation and genome turnover between mice and humans.

Alleles↗
PubMed1998

Influences of array size and homogeneity on minisatellite mutation.

Unstable minisatellites display high frequencies of spontaneous gain and loss of repeats in the human germline. Most length changes arise through complex recombination events including intra-allelic duplications/deletions and inter-allelic transfers of repeats. Definition of the factors modulating instability requires both measurement of mutation rate and detailed analysis of mutant structures at the level of individual alleles. We have measured mutation rates in sperm for a wide range of alleles of the highly unstable human minisatellite CEB1. Instability varies by three orders of magnitude between alleles and increases steadily with the size of the tandem array. Structural analysis of mutant molecules derived from six alleles revealed that it is the rate of intra-allelic rearrangements which increases with array size and that intra-allelic duplication events tend to cluster within homogeneous segments of alleles; both phenomena resemble features of trinucleotide repeat instability. In contrast, inter-allelic transfers occur at a fairly constant rate, irrespective of array length, and show a mild polarity towards one end of the minisatellite, suggesting the possible influence of flanking DNA on these conversion-like events.

Alleles↗
PubMed1998

Stage specificity, dose response, and doubling dose for mouse minisatellite germ-line mutation induced by acute radiation.

Germ-line mutation induction at mouse minisatellite loci by acute irradiation with x-rays was studied at premeiotic and postmeiotic stages of spermatogenesis. An elevated paternal mutation rate was found after irradiation of premeiotic spermatogonia and stem cells, whereas the frequency of minisatellite mutation after postmeiotic irradiation of spermatids was similar to that in control litters. In contrast, paternal irradiation did not affect the maternal mutation rate. A linear dose-response curve for paternal mutation induced at premeiotic stages was found, with a doubling dose of 0.33 Gy, a value close to those obtained in mice after acute spermatogonia irradiation using other systems for mutation detection. High frequencies of spontaneous and induced mutations at minisatellite loci allow mutation induction to be evaluated at low doses of exposure in very small population samples, which currently makes minisatellite DNA the most powerful tool for monitoring radiation-induced germ-line mutation.

Animals↗
PubMed1998

A novel unstable mouse VNTR family expanded from SINE B1 elements.

Human hypervariable minisatellites provide highly informative loci for analyzing processes of tandem repeat turnover, but little is known about mechanisms of instability in other species. We have therefore screened the mouse genome for analogous VNTR loci. One of the probes we isolated, MMS10, detects a highly variable rodent-specific family of multiple loci derived by expansion of a common GGCAGA repeat unit from within a subset of B1 short interspersed elements. The mean germline mutation rate for loci detected by MMS10 was estimated at 1.7% per offspring band, though analysis of individual loci showed substantial variation in germinal instability apparently related to repeat array size. This MMS10 family of expanded hexanucleotide repeat loci provides a novel resource for investigating mechanisms of tandem repeat turnover in the mouse and an efficient means for monitoring germline mutations induced by external agents such as ionizing radiation.

Animals↗
PubMed1998

High-resolution mapping of crossovers in human sperm defines a minisatellite-associated recombination hotspot.

Little is known about the fine-scale distribution of meiotic crossovers in human chromosomes. Methods have therefore been developed for detecting and mapping recombination products directly in human sperm DNA. Analysis of crossovers adjacent to the GC-rich minisatellite MS32, which is known to mutate by conversion and crossover within the repeat array, revealed an intense and highly localized recombination hotspot centered upstream of the locus and extending into the beginning of the minisatellite. Allele-specific cosuppression of crossovers and repeat instability suggests that the hotspot is responsible for driving repeat turnover at MS32 and thus that minisatellites might evolve as by-products of localized meiotic recombination in the human genome.

Alleles↗
PubMed1998

Radiation-induced germline instability at minisatellite loci.

PURPOSE: To review the results of recent studies on radiation-induced germline instability at mammalian minisatellite loci. RESULTS: Evidence has been obtained recently that germline mutation at minisatellites is remarkably sensitive to ionizing radiation, in both mice and humans. In mice, an elevated mutation rate was found after acute irradiation of pre-meiotic spermatogonia, with a doubling dose of 0.33 Gy, a value close to those obtained in mice after acute spermatogonia irradiation using other systems for mutation detection. In humans, analysis of germline mutation rate at minisatellites among children born in areas of the Mogilev district of Belarus, which was heavily polluted after the Chernobyl accident, has shown a twofold higher mutation rate in exposed families compared with non-irradiated families from the United Kingdom. Within the Belarus cohort, the mutation rate was significantly greater in families exposed to a higher parental radiation dose, consistent with radiation induction of germline mutation. The data in this study also demonstrate the indirect nature of radiation-induced germline mutation at mammalian minisatellite loci suggesting a strong similarity with the phenomenon of genomic instability in somatic cells. CONCLUSIONS: Minisatellite loci provide a powerful system for the efficient monitoring of germline mutation in humans and are capable of detecting induced mutations in relatively small population samples.

Animals↗
PubMed1997

Further evidence for elevated human minisatellite mutation rate in Belarus eight years after the Chernobyl accident.

Analysis of germline mutation rate at human minisatellites among children born in areas of the Mogilev district of Belarus heavily polluted after the Chernobyl accident has been extended, both by recruiting more families from the affected region and by using five additional minisatellite probes, including multi-locus probe 33.6 and four hypervariable single-locus probes. These additional data confirmed a twofold higher mutation rate in exposed families compared with non-irradiated families from the United Kingdom. An elevated rate was seen at all three independent sets of minisatellites (detected separately by multi-locus probes 33.15, 33.6 and six single-locus probes), indicating a generalised increase in minisatellite germline mutation rate in the Belarus families. Within the Belarus cohort, mutation rate was significantly greater in families with higher parental radiation dose estimated for chronic external and internal exposure to caesium-137, consistent with radiation induction of germline mutation. The spectra of mutation seen in the unexposed and exposed families were indistinguishable, suggesting that increased mutation observed over multiple loci arises indirectly by some mechanism that enhances spontaneous minisatellite mutation.

Adult↗