Highly polymorphic minisatellite sequences: allele frequencies and mutation rates for five locus-specific probes in a Caucasian population

Genetic effects of radiation in atomic-bomb survivors and their children: past, present and future

Genetic studies in the offspring of atomic bomb survivors have been conducted since 1948 at the Atomic Bomb Casualty Commission and its successor, the Radiation Effects Research Foundation, in Hiroshima and Nagasaki. Past studies include analysis of birth defects (untoward pregnancy outcome; namely, malformation, stillbirth, and perinatal death), chromosome aberrations, alterations of plasma and erythrocyte proteins as well as epidemiologic study on mortality (any cause) and cancer incidence (the latter study is still ongoing). There is, thus far, no indication of genetic effects in the offspring of survivors. Recently, the development of molecular biological techniques and human genome sequence databases made it possible to analyze DNA from parents and their offspring (trio-analysis). In addition, a clinical program is underway to establish the frequency of adult-onset multi-factorial diseases (diabetes mellitus, high blood pressure, and cardiovascular disease etc) in the offspring. The complementary kinds of data that will emerge from this three-pronged approach (clinical, epidemiologic, and molecular aspects) promise to shed light on health effects in the offspring of radiation-exposed people.

No evidence of radiation effect on mutation rates at hypervariable minisatellite loci in the germ cells of atomic bomb survivors

Human minisatellites consist of tandem arrays of short repeat sequences, and some are highly polymorphic in numbers of repeats among individuals. Since these loci mutate much more frequently than coding sequences, they make attractive markers for screening populations for genetic effects of mutagenic agents. Here we report the results of our analysis of mutations at eight hypervariable minisatellite loci in the offspring (61 from exposed families in 60 of which only one parent was exposed, and 58 from unexposed parents) of atomic bomb survivors with mean doses of >1 Sv. We found 44 mutations in paternal alleles and eight mutations in maternal alleles with no indication that the high doses of acutely applied radiation had caused significant genetic effects. Our finding contrasts with those of some other studies in which much lower radiation doses, applied chronically, caused significantly increased mutation rates. Possible reasons for this discrepancy are discussed.

DNA polymorphisms detect ancient barriers to gene flow in Basques

This work features the first district-by-district analysis of all provinces in the Iberian Peninsula with an autochthonous Basque population, and indicates the existence of genetic heterogeneity. The populations cluster in three groups arising from processes of genetic drift which probably occurred in pre-Mesolithic times, and were probably those which repopulated the southern areas of the Basque Country after the Last Glacial Maximum. It seems that from that period onwards, the population settled in three major groups (West Basques, Central Basques, and East Basques), along geographical axes which appear substantial in the maintaining of each population unit. This genetic structure is probably reflected in other aspects such as the existence of ancient tribes and the dialects of the Basque language, the boundaries of which may be related at origin and which are quite similar to those detected in this work. Our results indicate that the populations of the Basque Country are genetically close to other neighboring populations, such as that of Aragon, which may indicate an outgoing gene flow from the Basque area down the River Ebro towards the Mediterranean seaboard. While our short tandem repeat data suggest that population structure within the Basques dates back to the Mesolithic, our findings are also consistent with the hypothesis that patterns of modern European genetic diversity have been shaped mainly during the Neolithic.

Haplotype fine mapping by evolutionary trees

To refine the location of a disease gene within the bounds provided by linkage analysis, many scientists use the pattern of linkage disequilibrium between the disease allele and alleles at nearby markers. We describe a method that seeks to refine location by analysis of "disease" and "normal" haplotypes, thereby using multivariate information about linkage disequilibrium. Under the assumption that the disease mutation occurs in a specific gap between adjacent markers, the method first combines parsimony and likelihood to build an evolutionary tree of disease haplotypes, with each node (haplotype) separated, by a single mutational or recombinational step, from its parent. If required, latent nodes (unobserved haplotypes) are incorporated to complete the tree. Once the tree is built, its likelihood is computed from probabilities of mutation and recombination. When each gap between adjacent markers is evaluated in this fashion and these results are combined with prior information, they yield a posterior probability distribution to guide the search for the disease mutation. We show, by evolutionary simulations, that an implementation of these methods, called "FineMap," yields substantial refinement and excellent coverage for the true location of the disease mutation. Moreover, by analysis of hereditary hemochromatosis haplotypes, we show that FineMap can be robust to genetic heterogeneity.

Length and sequence variation in D7S22 (g3) alleles studied by high resolution length measurements and nucleotide sequencing

In a study of DNA sequence and length variation in the repeat array of small D7S22 alleles, 100 alleles typed as the common 14 repeat allele (14R) and 92 rare ones were selected for further characterization. A polymerase chain reaction (PCR) based allele length measurement method revealed a discontinuous distribution of alleles. The 92 rare alleles were grouped by their number of repeats. All, except four 6R alleles were distributed within the 11R-19R allele groups. The 14Rs revealed no further length variation while 7 out of the 92 rare alleles showed small length deviations from the other alleles within their respective groups. Nucleotide sequencing of the repeat array was performed in 17 alleles selected from each of the nine allele groups. The micro length variation within allele groups was caused by the presence of either 33, 36 or 37 bp repeats in given positions. A comparison of three 14Rs revealed no further sequence variation between these. Nine out of the fourteen repeats in the 14R differed in sequence and/or size. Based on this difference the repeat array sequence was converted into a code of different variant repeats. The 6R showed a variant repeat code quite unlike that of the 14R, while the encoded allele structure of the other rare alleles suggested that most of them may have evolved from a 14R allele by deletion or duplication of repeat units. Nucleotide sequencing of progenitor and mutant in a D7S22 de novo mutation as well as typing in a polymorphic site near the repeat array suggested that the event was an intra-allelic deletion of exactly three repeats. The present findings indicate that the 14R is ancestral to most rare small alleles, and that mutations in small alleles most often are intra-allelic events leading to a change in bp size equal to an integer number of repeats.

Population genetic and family data for the human minisatellite locus D16S309 (MS205) in Germans

The distribution of restriction fragments at the DNA minisatellite locus D16S309 was estimated by investigating blood samples from 2617 unrelated West German Caucasians and 1269 offspring. Furthermore segregation of fragments was studied in a large family and in trios. Altogether 2296 meioses were studied, revealing 7 paternal and 3 maternal mutations. Inspection of "phenotypes" did not reveal any remarkable deviation from Hardy-Weinberg equilibrium.

Analysis of allelic structures at the D7S21 (MS31A) locus in the Japanese, using minisatellite variant repeat mapping by PCR (MVR-PCR)

To sample the diversity of allelic structures at the D7821 (MS31 A) locus in the Japanese, allele-specific minisatellite variant repeat mapping using polymerase chain reaction (MVR-PCR) was performed on genomic DNA from a number of Japanese individuals. Three polymorphic positions in the MS31A 5' flanking DNA were typed from 214 un related Japanese, and the distribution of haplotypes was analysed. Allele-specific MVR-PCR using primers that discriminate between different alleles at these polymorphic positions in heterozygous individuals, allows single alleles to be mapped from genomic DNA in approximately 80% of Japanese. 149 Japanese alleles have been mapped to date and all of them, except for two pairs of indistinguishable alleles, have different internal structures. More than half of the mapped alleles showed similar regions of internal structure to other alleles and were classified into groups on this basis.

Population study of 3 STR loci in the Basque Country (northern Spain)

The tetrameric STRs, HUMTH01, HUMVWA31A and HUMFES/FPS, were studied in a population from the Basque Country (northern Spain) for their frequency distribution and applicability to identity and paternity testing. All systems conformed to Hardy-Weinberg equilibrium; pairwise comparisons demonstrated the allelic independence between loci, and furthermore, all systems seemed to be in agreement with expectations from the Stepwise Mutation Model (SMM) of the mutation-drift theory, which indicates the homogeneity of the population and suggests a replication slippage mechanism as a possible model for generating alleles. A comparison with other population groups appeared to indicate that frequencies are well conserved in Caucasians, but differ from other racial groups. The calculated parameters "a priori probability of exclusion" (PEX) and "index of discrimination" (ID), show the informativeness of these loci for the determination of identity and relatedness of individuals.

Allele frequency distribution for the variable number of tandem repeat locus D10S28 in Tamil Nadu (south India) population

Allele frequencies were determined in unrelated individuals of Tamil speaking population from the Madras City (Tamil Nadu, South India) area for the polymorphic DNA locus D10S28 using the probe TBQ7. Membranes hybridized with the probe YNH24 were subjected to deprobing and were subsequently hybridized with random priming - labeled, purified inserts of TBQ7. The sizes of the fragments were grouped to 100 bp as well as to arbitrary fixed bins (Federal Bureau of Investigation / Royal Canadian Mounted Police). There were 14 bins in the latter with the most common bin being 11 (1789-1924 bp) with a frequency of 9.8%. We observed a heterozygosity of 92% comparable to Caucasian populations. The data presented here can be used as the basis for utilizing this variable number of tandem repeats (TNTR) DNA marker for paternity determinations and forensic investigations.

Recent observations in human DNA-minisatellite mutations

We report maternal and paternal mutation rates at loci D1S7 (MS1), D7S21 (MS31), D12S11 (MS43A), and D7S22 (G3). The respective mutation rates were as follows: [table: see text] At loci D7S21, D12S11, and D7S22 statistically significant differences in mutation rates exist between the sexes. No such difference was observed at locus D1S7. However inspection of the latter data reveals that by mutation at spermiogenesis approximately two-thirds of the fragments showed an addition of repetitive units, while a 50: 50 ratio was encountered in the series of maternal mutations. We also report the observation of naturally occurring 3-fragment patterns.

Inference of population subdivision from the VNTR distributions of New Zealanders

A population sample from people of diverse ethnic origins living in New Zealand serves as a database to test methods for inference of population subdivision. The initial null hypothesis, that the population sample is homogeneous across ethnic groups, is easily rejected by likelihood ratio tests. Beyond this, methods for quantifying subdivision can be based on the probability of drawing alleles identical by descent (FST), probabilities of matching multiple locus genotypes, and occurrence of unique alleles. Population genetic theory makes quantitative predictions about the relation between FST, population sizes, and rates of migration and mutation. Some VNTR loci have mutation rates of 10(-2) per generation, but, contrary to theory, we find no consistent association between the degree of population subdivision and mutation rate. Quantification of population substructure also allows us to relate the magnitudes of genetic distances between ethnic groups in New Zealand to the colonization history of the country. The data suggests that the closest relatives to the Maori are Polynesians, and that no severe genetic bottleneck occurred when the Maori colonized New Zealand. One of the central points of contention regarding the application of VNTR loci in forensics is the appropriate means for estimating match probabilities. Simulations were performed to test the merits of the product rule in the face of subpopulation heterogeneity. Population heterogeneity results in large differences in estimates of multilocus genotype frequencies depending on which subpopulation is used for reference allele frequencies, but, of greater importance for forensic purposes, no five locus genotype had an expected frequency greater than 10(-6). Although this implies that a match with an innocent individual is unlikely, in a large urban area such chance matches are going to occur.

Chemically induced changes in the spectrum of amplifications of the human minisatellite MS1 integrated in chromosome III of a haploid yeast strain

To study chemically induced DNA amplifications we used the haploid Saccharomyces cerevisiae strain TR(MS1)-1 carrying an integrated chromosomal copy of the human minisatellite. MS1. Chemicals with different mechanisms of action were tested in this strain: methyl methanesulphonate, ethylene oxide (EO), propylene oxide (PO), camptothecin, 2,3,7,8-tetrachlorodibenso-p-dioxin (TCDD) and reserpine. No increase in frequency of new MS1 length alleles was seen with any of the tested chemicals relative to the spontaneous frequency of approximately 30%. EO and TCDD induced changes in the amplification spectrum, i.e., the frequency distribution of MS1 length alleles longer than the original 1.42 kb allele. PO and camptothecin increased the frequency of plasmid "pop-out" events. It seems likely that several mechanisms e.g. unequal exchanges, replication slippage and loop formation leading to deletion of a ring of tandem repeats, are involved in the generation of new MS1 length alleles. A loop-forming deletion mechanism is supported by the tendency to multimodality shown in the deamplification (loss of repeat units) spectra, i.e. the frequency distribution of new MS1 length alleles shorter than the original allele. EO and TCDD induced "longer" MS1 length alleles as compared to the control. The frequent generation of new MS1 length alleles in this haploid yeast strain further demonstrates the instability of such sequences and their possible relevance to genetic toxicology and the mechanisms of induction of cancer as well as other diseases. This study is a first step towards the development of an assay for DNA amplification without the use of a selective agent.

Amplified fragment length polymorphism analysis of the VNTR locus D1S80 in central Spain

The polymorphism of the D1S80 locus has been analyzed in a population sample of 203 unrelated individuals living in Madrid (central Spain) by PCR and subsequent semi-dry discontinuous polyacrylamide gel electrophoresis (Tris-chloride/Tris-glycine buffer system) followed by silver staining. The electrophoretic system described in this study offers high resolution in the separation of the different D1S80 alleles allowing the detection of microvariability around the allele T22 in the spanish population. Twenty different alleles containing 17-40 repeats of the basic 16 bp unit were distinguished. The alleles T18 and T24 were found to be relatively common in Spain, as in other populations, with frequencies of 0.224 and 0.372, respectively. No evidence of significant deviations from Hardy-Weinberg equilibrium was found in these preliminary population data.

Paternity testing with VNTR DNA systems. I. Matching criteria and population frequencies of the VNTR systems D2S44, D5S43, D7S21, D7S22, and D12S11 in Danes

Paternity testing using DNA polymorphism of variable numbers of tandem repeat (VNTR) regions with restriction fragment length polymorphism (RFLP) was implemented. HinfI-digested DNA was separated by electrophoresis in agarose gels and hybridized with radiolabelled probes detecting the VNTR-systems D2S44 (YNH24), D5S43 (MS8), D7S21 (MS31), D7S22 (g3), and D12S11 (MS43a). The intra gel variability of 970 duplicate investigations on the same gel of DNA from 122 individuals showed no differences exceeding 1.25 mm between the positions of the corresponding DNA fragments. The comparison of 1,624 DNA fragments from 342 mother/child pairs showed only one difference above 1.25 mm which was interpreted as a mutation. Based on these observations, we decided to consider an intra gel difference above 1.25 mm between the non-maternal DNA fragment of the child and the nearest DNA fragment of the putative father as an exclusion in paternity testing. This matching criterion was used for the comparisons of 1,197 DNA fragment differences in 247 pairs of children and putative fathers who had not been excluded by conventional marker systems. In all of these cases, the migration differences between the DNA fragments of non-excluded men and the DNA fragments of the children were less than 1.25 mm except in 6 cases (0.5%). The man/child differences in all of 227 false trios exceeded 1.25 mm in 2 or more of the 5 VNTR systems investigated. Matching criteria for inter gel comparisons in paternity testing were established. The frequency distribution of HinfI digested DNA fragments of the 5 VNTR systems in 650 unrelated Danes is presented and the raw data is available.

DNA-minisatellite mutations: recent investigations concerning distribution and impact on parentage testing

At least 815 meioses were studied in the HinfI polymorphisms of DNA minisatellite loci D1S7, D2S44, D7S21, D7S22, and D12S11 in order to collect data on respective mutation rates. At locus D7S21 (probe MS31) a striking difference between the paternal and maternal mutation rate was observed (1.5% versus 0.2%). This study also describes, how to deal biostatistically with paternal mutations in parentage testing. Possible implications of mutations are illustrated by the description of 2 cases. Case 1 reports an "exclusion" of mother and father with probe MS1. Case 2 describes 2 paternal "exclusions" with probes MS31 and G3. The statistical likelihood for a paternal "exclusion" with 2 of the 5 probes is 0.13%. By omitting probe MS1, this frequency can be reduced to 0.02%. Nevertheless, the second case clearly shows, that informative blood group markers cannot be replaced by DNA polymorphisms.

Paternity testing with VNTR DNA systems. II. Evaluation of 271 cases of disputed paternity with the VNTR systems D2S44, D5S43, D7S21, D7S22, and D12S11

Paternity testing was carried out in 271 cases of disputed paternity using the 5 VNTR systems D2S44 (YNH24), D5S43 (MS8), D7S21 (MS31), D7S22 (g3), and D12S11 (MS43a), and 10-15 conventional marker systems including the HLA-A,B system. By means of the matching criteria for the VNTR systems established elsewhere (Morling & Hansen 1992), all 70 unrelated men who had been excluded by conventional typing were also excluded with 2 or more VNTR systems. Based on the observed exclusion frequencies for the 5 VNTR systems, a theoretical exclusion rate exceeding 0.999 could be obtained. A total of 350 father/child pairs were studied and in 3 paternity cases and one immigrant family, the alleged fathers were excluded solely by one of the 5 VNTR systems possibly reflecting mutations. No mother/child exclusions were observed among 350 mother/child pairs. Linkage analysis between the syntenic systems D7S21 (MS31) and D7S22 (g3) was performed in 29 informative families with 81 children and revealed a recombination distance of about 31 cM. The positive evidence for paternity provided by the 5 VNTR systems in cases with non-exclusions is discussed.

Genetic investigations in immigration cases and frequencies of DNA fragments of the VNTR systems D2S44, D5S43, D7S21, D7S22, and D12S11 in Turks

We have included investigations of the DNA polymorphism of variable numbers of tandem repeat (VNTR) regions with restriction fragment length polymorphism (RFLP) in the genetic evaluations in immigrant cases. HinfI-digested DNA was separated by electrophoresis in agarose gels and hybridized with radiolabelled probes detecting the VNTR systems D2S44 (YNH24), D5S43 (MS8), D7S21 (MS31), D7S22 (g3), and D12S11 (MS43a). We used the matching criterion for paternity testing for the parent/child comparisons, i.e. non-match if the intra gel difference exceeded 1.25 mm. A total of 43 immigration cases involving mainly Turks were investigated with DNA technique in parallel with investigations of 10-15 conventional systems. One man was excluded from paternity by both conventional and DNA investigations. Non-exclusion was observed with both conventional and DNA systems in 97 putative mother/child pairs and in 96 putative father/child pairs. In a putative father/child combination with non-exclusion in 18 genetic systems, a single genetic inconsistency ('exclusion') in D7S21 (MS31) was observed. The frequency distributions of HinfI digested DNA fragments of the five VNTR systems in 105 Turks are presented.

Analysis of a Danish Caucasian population sample of single locus DNA-profiles. Allele frequencies, frequencies of DNA-profiles and heterozygosity

The frequency distributions of the length of restriction fragments (HinfI) revealed by RFLP-analysis (restriction fragment length polymorphism) of blood samples from 482 Danish Caucasians using the single locus VNTR (variable number of tandem repeats) probes MS1, MS31, MS43a and YNH24 are reported. From two blood samples three fragments were obtained with MS1. The consistency of the characteristic allele frequency distribution for each probe is exemplified by comparing the accumulated frequency curves obtained with MS43a in samples consisting of 50 and 920 bands, respectively. The distribution of the differences in migration distance for the two fragments of a bandpair was investigated. The results suggest that the high frequency of apparent homozygotes observed is due mainly to coalescence of close heterozygotes. The distribution of frequencies of 437 DNA-profiles is reported.

Isérables: a Bedouin village in Switzerland?

Isérables is an alpine village--about 1000 inhabitants--which remained isolated till these recent years because of its particular geographical situation. The Isérables inhabitants call themselves "Bedjuis" (Bedouin in local dialect) and regard themselves as descendants of the Sarrazins who invaded the Alps during the VIII-X centuries. Our goal, in studying several DNA-VNTR polymorphims, in addition to some blood groups, within the Isérables community, was to see if there was any evidence supporting this popular belief. As a preliminary phase of this project, the allelic frequencies for six VNTR loci analysed for 102 individuals of the village (all descendants of nine original families) are presented. The results are compared with those reported for Swiss and white populations.

Chemiluminescent DNA probes: evaluation and usefulness in forensic cases

Five phosphatase-labelled oligonucleotide probes were evaluated in respect to their sensitivity, with the help of an optimized chemiluminescent protocol, for DNA-VNTR polymorphism determination. Their usefulness for the identification of biological traces is illustrated with casework examples.

Yeast artificial chromosomes (YACs) and the analysis of complex genomes

The development of yeast artificial chromosome (YAC) cloning vectors capable of carrying several hundred kilobase-pairs of DNA insert has greatly facilitated the study of complex genomes, and the cloning of large genes as single fragments. In addition, the ability to manipulate YAC sequences by homologous recombination makes this system extremely useful for the generation of disease models.

Molecular biology in medicine

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Forensic applications

The introduction of DNA based identity testing has revolutionized the field of forensic analysis of biological materials. Most of the publications during the past year expand earlier studies that began more than seven years ago, on the properties of DNA recovered from different types of evidential materials; these studies examine the suitability of these samples for identity testing, the effect of different environmental insults the population genetics of loci used for identity testing, and the methods used for statistical analysis of the DNA patterns.

Human minisatellite alleles detectable only after PCR amplification

We present evidence that a proportion of alleles at two human minisatellite loci is undetected by standard Southern blot hybridization. In each case the missing allele(s) can be identified after PCR amplification and correspond to tandem arrays too short to detect by hybridization. At one locus, there is only one undetected allele (population frequency 0.3), which contains just three repeat units. At the second locus, there are at least five undetected alleles (total population frequency 0.9) containing 60-120 repeats; they are not detected because these tandem repeats give very poor signals when used as a probe in standard Southern blot hybridization, and also cross-hybridize with other sequences in the genome. Under these circumstances only signals from the longest tandemly repeated alleles are detectable above the nonspecific background. The structures of these loci have been compared in human and primate DNA, and at one locus the short human allele containing three repeat units is shown to be an intermediate state in the expansion of a monomeric precursor allele in primates to high copy number in the longer human arrays. We discuss the implications of such loci for studies of human populations, minisatellite isolation by cloning, and the evolution of highly variable tandem arrays.

Murder in south London: a novel use of DNA profiling

Lorraine Benson's body was found beaten and strangled at Raynes Park, Surrey, in December 1988. Considering the possibility of linked offences, a murder squad was set up to work alongside a team already investigating a rape series in the Kingston area. A man's handkerchief left at a site a quarter of a mile from the murder scene was found to be stained with blood and saliva matching that of the victim. A DNA profile was obtained from a stain of nasal mucus on this handkerchief and found to match a suspect later arrested for an attempted rape in the same locality. Also of forensic interest were dust marks made by the zips of the victim's and defendant's coats and identification of the rope used for strangulation.

Statistical analysis of the measurement errors in the determination of fragment length in DNA-RFLP analysis

DNA from human whole blood samples was digested with the restriction enzyme HinfI and RFLP analysis performed using the single locus probes MS1, MS31, MS43a and YNH24. The intergel variation of 3291 duplicate measurements of fragment lengths in terms of basepairs was investigated. The difference between two measurements of the same fragment on different gels increased approximately exponentially with increasing fragment length. After transformation of the fragment length into a normalized migration distance it was found that the difference between two transformed measurements was normally distributed with a S.D. (0.70 mm) which was independent of the fragment length. The errors of band 1 and band 2 on the same lane were correlated (r2 = 0.8). It is useful in the calculation of frequencies and in retrieval procedures and also in the calculation of likelihood ratios to be able to use a S.D. which is independent of the fragment length.

Minisatellite repeat coding as a digital approach to DNA typing

Most DNA typing systems used in forensic and legal medicine assay allelic length variation at tandem repetitive DNA regions such as minisatellites. A simple alternative approach that displays patterns of variant repeat units along minisatellite alleles is described here. This produces DNA profiles as extraordinarily variable digital sequences appropriate for forensic investigations, including computer databasing, and for analysing allele diversity and the role of recombination in minisatellite instability.

DNA investigations on fetal material from paternity cases

Three paternity cases have been investigated where DNA was extracted from fetuses (age: 8-10 weeks old) after interruption of pregnancy. In each case it was possible to clearly identify the putative father using 5 or 6 single locus probes (SLP's). Fetal bands (SLP) could be clearly identified from mixtures of placental and fetal DNA by comparison with the maternal and paternal bands. However, it was very difficult to resolve the fragment patterns of tissue mixtures with one multi locus probe (MLP), because of band overlap. Another advantage of using SLP's was that biostatistical calculations could be carried out and very informative Essen-Möller values for the probability of paternity were obtained.

The distribution of the HLA-DQ alpha alleles and genotypes in the Finnish population as determined by the use of DNA amplification and allele specific oligonucleotides

Allele and genotype frequencies for the HLA-DQ alpha locus were determined for use in forensic analyses and paternity tests in Finland. The polymerase chain reaction (PCR) and the reverse dot blot format were employed to detect 6 different HLA-DQ alpha alleles. All 6 HLA-DQ alpha alleles were detected among the 112 unrelated individuals with allele frequencies ranging from 5.8% to 32.6%. The distribution of the observed genotypes is in Hardy-Weinberg equilibrium. Additionally, this Finnish population sample is statistically similar to 2 other Caucasian sample populations. The power of discrimination of this system in the Finnish population sample is 0.92, suggesting this method may prove suitable for identification purposes.

Elucidation of apparent non-maternity with DNA probes detecting highly polymorphic single locus systems

During paternity testing, we encountered the following constellation in the Jk system: the mother's phenotype was Jk(a-b+), while the son was typed as Jk(a+b-). The deduced genotype of the mother would have been Jkb Jkb, and each offspring should then express the Jk(b) antigen. Consequently, non-maternity would be deduced. Since no material was available for extended family studies or HLA typing, except for the DNA of the propositi, only RFLP analysis could bring clarification in this case. The application of four highly polymorphic single locus probes proved the maternity and hence the existence of a Jk-Null allele. We conclude that direct testing at the DNA level may help resolving cases where, by conventional parentage testing, conclusive results are unachievable because of putative 'Null' alleles.

Population and family data of RFLP's using selected single- and multi-locus systems

The multi-locus systems (MLS) 33.15 and 33.6 (Jeffreys et al 1985a) and the single-locus systems (SLS) MS 1, MS 8, MS 31 and MS 43 (Wong et al. 1987) were investigated. The number of bands and the rate of band sharing were determined for both multi-locus systems and compared to the results of an English survey. Additionally 73 families were investigated using the multi-locus probes and the results compared to those obtained for the traditional blood grouping systems. The results were in full agreement so that no evidence of new mutations could be found. The fragment distribution was calculated for each of the 4 single-locus systems and compared to the values reported in an English survey (Smith et al. 1990b). Distinct discrepancies were seen in the systems MS 1 and MS 8. Family analyses were carried out for the 4 single-locus systems and compared to English data (Jeffreys et al. 1988) to look for any indications of possible new mutations. Only one isolated exclusion could be demonstrated with MS 1.

Highly polymorphic minisatellite DNA probes. Further evaluation for individual identification and paternity testing

Reliable and reproducible protocols have been developed for the routine DNA fingerprinting of individuals using the highly polymorphic minisatellite DNA probes 33.15 and 33.6. Comparison of DNA fingerprinting from 50 individuals has generated further data on the level of band sharing in the DNA fingerprints of unrelated individuals, as well as the number of bands scorable in individuals. These results are consistent with previous studies. The occurrence of mutant bands in offspring has been examined in over 100 families. Further support is presented for the Mendelian inheritance of minisatellite loci and for lack of significant allelism and linkage between different variable DNA fragments detected in a human DNA fingerprint.

Molecular characterisation of three alpha-1-antitrypsin deficiency variants: proteinase inhibitor (Pi) nullcardiff (Asp256----Val); PiMmalton (Phe51----deletion) and PiI (Arg39----Cys)

Three mutations causing alpha-1-antitrypsin deficiency have been identified by gene amplification and direct DNA sequencing. In the Pi (proteinase-inhibitor) nullcardiff gene, the codon for aspartate at position 256 has mutated to encode valine. In PiMmalton and Pi I, the respective mutations are the deletion of the codon for a phenylalanine residue at position 51 or 52, and a single base substitution resulting in arginine being replaced by cysteine at position 39. Examination of the protein tertiary structure suggests that all of these mutations are likely to result in folding abnormalities that may explain the deficiency states.