Mpi Locus Research Articles

Footprints of natural selection at the mannose-6-phosphate isomerase locus in barnacles

The mannose-6-phosphate isomerase (Mpi) locus in Semibalanus balanoides has been studied as a candidate gene for balancing selection for more than two decades. Previous work has shown that Mpi allozyme genotypes (fast and slow) have different frequencies across Atlantic intertidal zones due to selection on postsettlement survival (i.e., allele zonation). We present the complete gene sequence of the Mpi locus and quantify nucleotide polymorphism in S. balanoides, as well as divergence to its sister taxon Semibalanus cariosus We show that the slow allozyme contains a derived charge-altering amino acid polymorphism, and both allozyme classes correspond to two haplogroups with multiple internal haplotypes. The locus shows several footprints of balancing selection around the fast/slow site: an enrichment of positive Tajima's D for nonsynonymous mutations, an excess of polymorphism, and a spike in the levels of silent polymorphism relative to silent divergence, as well as a site frequency spectrum enriched for midfrequency mutations. We observe other departures from neutrality across the locus in both coding and noncoding regions. These include a nonsynonymous trans-species polymorphism and a recent mutation under selection within the fast haplogroup. The latter suggests ongoing allelic replacement of functionally relevant amino acid variants. Moreover, predicted models of Mpi protein structure provide insight into the functional significance of the putatively selected amino acid polymorphisms. While footprints of selection are widespread across the range of S. balanoides, our data show that intertidal zonation patterns are variable across both spatial and temporal scales. These data provide further evidence for heterogeneous selection on Mpi.

Genetic Variation in the Acorn Barnacle from Allozymes to Population Genomics

Understanding the patterns of genetic variation within and among populations is a central problem in population and evolutionary genetics. We examine this question in the acorn barnacle, Semibalanus balanoides, in which the allozyme loci Mpi and Gpi have been implicated in balancing selection due to varying selective pressures at different spatial scales. We review the patterns of genetic variation at the Mpi locus, compare this to levels of population differentiation at mtDNA and microsatellites, and place these data in the context of genome-wide variation from high-throughput sequencing of population samples spanning the North Atlantic. Despite considerable geographic variation in the patterns of selection at the Mpi allozyme, this locus shows rather low levels of population differentiation at ecological and trans-oceanic scales (F(ST) ~ 5%). Pooled population sequencing was performed on samples from Rhode Island (RI), Maine (ME), and Southwold, England (UK). Analysis of more than 650 million reads identified approximately 335,000 high-quality SNPs in 19 million base pairs of the S. balanoides genome. Much variation is shared across the Atlantic, but there are significant examples of strong population differentiation among samples from RI, ME, and UK. An F(ST) outlier screen of more than 22,000 contigs provided a genome-wide context for interpretation of earlier studies on allozymes, mtDNA, and microsatellites. F(ST) values for allozymes, mtDNA and microsatellites are close to the genome-wide average for random SNPs, with the exception of the trans-Atlantic F(ST) for mtDNA. The majority of F(ST) outliers were unique between individual pairs of populations, but some genes show shared patterns of excess differentiation. These data indicate that gene flow is high, that selection is strong on a subset of genes, and that a variety of genes are experiencing diversifying selection at large spatial scales. This survey of polymorphism in S. balanoides provides a number of genomic tools that promise to make this a powerful model for ecological genomics of the rocky intertidal.

Genetic differentiation in Sorex: Electrophoretic analysis of the karyotypic races of Sorex araneus in Sweden

The common shrew, Sorex araneus L., is in Sweden represented by animals of three karyotypic races. The chromosomal differences are due to Robertsonian changes and are not accompanied by any obvious morphological differences. Animals from six populations (two from each karyotypic race) were analyzed chromosomally and electrophoretically. A total number of 225 animals were used in the electrophoretic investigation. Of the 27 loci studied, 24 showed no or only little electrophoretic variation. Three loci were clearly polymorphic but showed no allele difference diagnostic for any of the karyotypic races. However, one of the alleles at the Mpi locus, with a frequency between 0.20 and 0.40 in the southern and central races, was not found in the northern race. At this locus, there was also a difference between the northern and the other two races for the most common allele. Comparison of this result with information from other chromosomally variable mammalian species shows that normally only small electrophoretic differences exist between karyotypic races belonging to the same species.

Genetic studies of Gammarus

The marine amphipods Gammarus salinus and G. oceanicus are both polymorphic at the enzyme loci glucosephosphate isomerase (Gpi), glutamic-pyruvic transaminase (Gpi), and mannosephosphate transaminase (Mpi). In addition, G. solinus is polymorphic at the glutamic-oxaloacetic transaminase locus Gotl. The variation at these loci is described for populations ranging from the Limfjord, Denmark, to the Baltic Sea at Askô, Sweden. In both species the Baltic populations and the Kattegat populations have diverged from each other. The populations are connected through gene frequency clines that can be smooth (at the Gpi locus in both species) or more irregular (at the Mpi locus in both species).

Genetic studies of Gammarus. IV. Selection component analysis of the Gpi and the Mpi loci in Gammarus oceanicus.

The population of the marine amphipod Gammarus oceanicus at Vosnaes, Denmark, is polymorphic at the two unlinked enzyme loci mannosephosphate isomerase. Mpi, and glucosephosphate isomerase, Gpi. These polymorphisms were subjected to a selection component analysis, where the components gametic selection, zygotic selection, and sexual selection were estimated in both sexes and where the mating pattern was described. At the Gpi locus no evidence of the action of natural selection was found. The genotypic distribution among the adult population at the Mpi locus did not agree with the expected distribution under the assumption of no selection. A significant deficit of heterozygotes was found. This deviation, however, is explained by the segregation of a silent allele.

Hybridization Between Parthenogenetic Lizards (Aspidoscelis neomexicana) and Gonochoristic Lizards (Aspidoscelis sexlineata viridis) in New Mexico: Ecological, Morphological, Cytological, and Molecular Context

Whiptail lizard guilds consisting of different combinations of parthenogenetic Aspidoscelis exsanguis, Aspidoscelis neomexicana, and Aspidoscelis tesselata pattern classes C and D and gonochoristic Aspidoscelis sexlineata viridis inhabit numerous sites in the immediate vicinity of Conchas Lake, San Miguel County, New Mexico. Based on morphological identification by other workers of specimens collected in 1978, A. neomexicana was the species most recently added to the list of whiptail lizards known to occur at Conchas Lake, about 190 km east of its main distribution area in the Rio Grande Valley. We sampled guilds consisting of A. neomexicana and its congeners at Conchas Lake from 2000 through 2003. In 2002 we also collected specimens of what appeared to be another tokogenetic array of A. neomexicana east of the Rio Grande Valley in syntopy with A. tesselata E and A. sexlineata viridis at Fort Sumner, De Baca County, New Mexico. Comparison of karyotypes revealed that individuals of A. tesselata and those assigned by their discoverers to A. neomexicana from Conchas Lake and Fort Sumner have identical diploid karyotypes (2n = 46) that include diagnostic haploid complements of chromosomes derived from independent hybridizations between species in the tigris and sexlineata species groups. Consequently, we used electrophoretic data for 23 gene loci, of which the sMDH, sMDHP, sIDH, ESTD, PEPA, PEPB, ADA, MPI, GPI, and PGM2 loci were definitive, to further validate the hypothesis that the disjunct groups of putative A. neomexicana in eastern New Mexico had been correctly identified. The specimens analyzed electrophoretically also indicated that the Conchas Lake clone of A. neomexicana is identical to the most widely distributed clone of the species in the Rio Grande Valley of New Mexico and that the Fort Sumner clone possessed a distinctive allele.We describe the habitat for A. neomexicana at Conchas Lake at three sites north of the Canadian River and two sites south of the river. Two of the sites north of the Canadian River were studied as examples of guilds that did not include A. sexlineata viridis. The latter species was observed with A. neomexicana, A. tesselata, and A. exsanguis at one site north of the Canadian River and two sites south of the river. At Fort Sumner, we studied A. neomexicana at two sites where it was syntopic with A. tesselata E and A. sexlineata viridis.We identified 15 lizards from three sites at Conchas Lake as hybrids of A. neomexicana × A. sexlineata viridis. Most of these hybrids were found in either patchy or weedy chronically disturbed habitats in which the parental forms were forced into unusually close syntopic relationships. Hybrids between these parental forms were collected in each year from 2000– 2003 and represented a minimum of four and a maximum of five generations.Although hybrids of A. neomexicana × A. sexlineata viridis were characterized by distinctive color patterns, all were rather similar to maternal parent A. neomexicana, but with modifications resulting from the genetic contribution of its paternal parent A. sexlineata viridis. All specimens identified as hybrids by color pattern also possessed meristic characters that distinguished them from both parental forms. Univariate and multivariate analyses of scutellation also revealed evidence of the genetic effects of the parental species on the hybrids.One live hybrid male of A. neomexicana × A. sexlineata viridis was collected at Conchas Lake. The hybrid (American Museum of Natural History R-151739) was a triploid (3n = 69) including the complete diploid complement of A. neomexicana (= A. tigris marmorata × A. inornata) plus a second haploid complement of sexlineata group chromosomes. Karyotypically, in all details this triploid appeared to be an F1 hybrid of A. neomexicana × A. sexlineata viridis. This confirmed hybrid possessed a similar array of color pattern and scutellation characters observed in the other individuals of presumptive

Host-plant-associated genetic differentiation in Northern French populations of the European corn borer.

The phytophagous insects that damage crops are often polyphagous, feeding on several types of crop and on weeds. The refuges constituted by noncrop host plants may be useful in managing the evolution in pest species of resistance to the Bacillus thuringiensis toxins produced by transgenic crops. However, the benefits of these refuges may be limited because host-plant diversity may drive genetic divergence and possibly even host-plant-mediated sympatric speciation. The European corn borer, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), is the main pest of maize in Europe and North America, where it was introduced early in the 20th century. It has a wide host range but feeds principally on mugwort (Artemisia vulgaris L.) and maize (Zea mays L.). O. nubilalis is found on mugwort only in the northern part of France, whereas it is found on maize throughout France. The extent of genetic variation at allozyme markers was investigated in populations collected from the two host plants over the entire geographical distribution of the European corn borer on mugwort in France. Allelic differentiation between pairs of populations and hierarchical analyses of pools of samples from each host plant indicate that the group of populations feeding on maize differed from the group of populations feeding on mugwort. Our results suggest (1) host-plant-related divergent selection at the genomic region surrounding the Mpi locus and (2) limited gene flow between the populations feeding on mugwort and those infesting maize fields. These data indicate that adults emerging from mugwort would not be useful for managing the evolution of resistance to the B. thuringiensis toxins in European corn borer populations.

The effects of diet and physiological stress on the evolutionary dynamics of an enzyme polymorphism.

In the northern acorn barnacle Semibalanus balanoides, polymorphism at the mannose-6-phosphate isomerase (Mpi) locus appears to be maintained by distinct selection regimes that vary between intertidal microhabitats. The goal of the present experiment was to elucidate the mechanism of selection at the Mpi locus by examining the relationship between genotype and fitness-related life-history traits in laboratory manipulations. When barnacles were cultured on a mannose-supplemented diet and exposed to thermal stress, different Mpi genotypes exhibited differences in the rate of growth that predicted survivorship. In contrast, no such relationship was observed in control or fructose-supplemented dietary treatments either in the presence or in the absence of stress. Similarly, the phenotype and survivorship of genotypes at another allozyme locus and a presumably neutral mitochondrial DNA marker were homogeneous across all treatments and unaffected by experimental manipulations. These results suggest that the differential survivorship of Mpi genotypes in the field and laboratory results from a differential ability to process mannose-6-phosphate through glycolysis. The widespread polymorphism at Mpi observed in marine taxa may reflect the interaction between dietary composition and environmental heterogeneity in intertidal habitats.

The sexually linked Mpi locus is presumably involved in imidothiazole resistance in Oesophagostomum dentatum parasites.

Information about genetic changes during the selection process could indicate mechanisms underlying the spread of resistance to anthelmintic drugs. For clarification of the role of the Mpi locus encoding mannose-phosphate isomerase enzyme in determining resistance, genotyping of Oesophagostomum dentatum strains was performed using an isoelectrofocusing technique. In levamisole- and pyrantel-selected strains the allele associated with resistance has probably been found. Significant values for genetic differentiation between treated and untreated strains of common origin were recorded by F(st) indices (theta = 0.078; P = 0.0008). The specific genomic makeup of a flubendazole-resistant strain, which did not correlate with that of the remaining isolates, might be ascribed to a different action of the anthelmintic or different environmental conditions under which resistance against this drug arose. The absence of heterozygotes in male populations indicated an XX/X0 system of sex determination for the Mpi locus, thus providing a greater potential for the development of resistance. A possible involvement of alleles linked with mannose-phosphate isomerase in alterations of membrane receptors that can be associated with resistance against imidothiazole-based drugs is discussed.

The use of allozymes and shell morphology to distinguish among sympatric species of the rock oyster Saccostrea in Thailand

Three hundred and fifty-five Saccostrea oysters from 12 sites throughout Thailand were scored for allozyme variation at eight enzyme loci ( Aat-1, Ap, Est-2, Lap, Mdh-1, Mpi, Pgi and Pgm). Allelic variation within Lap, Pgi, Pgm and Mpi loci was concordant. Principle component analysis (PCA) of these four loci identified two principal components (PC1 and PC2) that resolved individuals into three discrete clusters corresponding to different species. Oysters were assigned to different species by diagnostic alleles at Lap, Mpi and Pgi loci, and correct identification confirmed by a comparison of observed genotype frequencies in putative single-species samples with those expected under Hardy–Weinberg equilibrium. We identified one of these species as Saccostrea commercialis, based on identical mobility's at all eight loci to a reference sample of that species from Australia. The other two species we identified as S. cucullata and S. manilai by comparison of relative allozyme mobility's and shell morphology traits with data published for these species. S. commercialis and S. manilai were found in sympatry in coastal and estuarine sites throughout the Gulf of Thailand. S. cucullata was restricted to offshore islets. Ten measurements were made on the shells of a subset of oysters from seven sites. Observations were also made of adductor scar colour and chomata spacing. Principal component analysis of shell morphometrics of ninety oysters identified by allozymes revealed three principal components that varied between species. These reflected variation in overall size, degree of “cupping” of left valve, and relative size of the umbo cavity. The most useful character for species identification was the size of the umbo cavity, which was large in S. cucullata and S. commercialis, but almost non-existent in S. manilai. Mean umbo depths were 1.49 cm for S. cucullata, 0.7 cm for S. commercialis and 0.42 cm for S. manilai. Colour of the adductor scar was also of taxonomic value, with 75% of S. cucullata having black scars, while scars were white or brown in the other two species.

Genetic diversity and speciation ofrana rugosa(amphibia; ranidae)

Horizontal starch gel electrophoresis for 29 populations (n=543) of the wrinkled frog, Rana rugosa, from Korea and Japan was performed to assess the degree of genic variation and genetic diversity, and to understand the biogeographic pattern of distribution and speciation. A sum of 22 presumptive loci was screened from 17 enzymes and general proteins. Four loci, Aco, Est‐3, Me‐2, and Pgm, demonstrated high levels of polymorphism. The degree of average genetic variation of R. rugosa was P=22.7% (9.1–40.9%), Ho=0.086 (0.048–0.165) and He=0.090 (0.042–0.168). In the south‐eastern region of the Korean peninsula (Chongsong, Yongchon, Ulsan, Kyongju, Pohang, Yongdok and Ulchin), a few unique alleles in the Mpi locus were detected and their biogeographic implications were considered. The degree of genetic differentiation among the Korean populations was moderate (S=0.900), whereas the degree of genetic diversity between Korean and Japanese populations was notably high (S=0.687, D=0.293). This result corresponds with the data obtained by the mitochondrial cytochrome b gene sequence (Lee et al., 1999) suggesting that the Korean and Japanese R. rugosa might have evolved a specific level of genetic differentiation since their geographic isolation.

INTERTIDAL MICROHABITAT AND SELECTION AT MPI: INTERLOCUS CONTRASTS IN THE NORTHERN ACORN BARNACLE, SEMIBALANUS BALANOIDES.

Barnacles were sampled from various microhabitats in the rocky intertidal at multiple sites in two years. At sites in which there were large differences among microhabitats in temperature profiles, Mpi genotype frequencies were consistently and significantly different. Genotype frequencies for another allozyme locus (Gpi) as well as a DNA marker shown to be neutral (the mtDNA control region) were statistically homogeneous among thermal microhabitats at all sites in both years. The data indicate that temperature and/or desiccation mediated selection is operating at Mpi or a linked locus and that Mpi genotypes experience differential mortality in the various habitat types. If the relative fitness of genotypes is dependent on habitat type, the Mpi polymorphism may be actively maintained by a Levene model of balancing selection (Levene 1953). Because barnacle larvae are produced in abundance each year and spend five to eight weeks dispersing in the water column, there is little opportunity for the accumulation of adaptive divergence over the environmental grain size relevant in intertidal habitats. The Mpi polymorphism may be an important component of a suite of traits involved in the adaptation of barnacles to heterogeneous environments. Due to the relatively high concentration of mannose in a variety of algal groups, the metabolism of mannose may substantially affect individual performance and fitness in this and other species that feed on algae and phytoplankton. Because the Mpi locus is one of the most strongly polymorphic in marine organisms, these findings may be relevant for a diversity of other such species.

Selection and population genetic structure of the barnacle Semibalanus balanoides in the northwest Atlantic and Gulf of St. Lawrence

It has been proposed that population genetic structure at the mannose-6-phosphate isomerase (Mpi) locus in the barnacle Semibalanus balanoides (L.) could be due to selection by ice scour acting through variation in larval settlement behavior. Homogeneity of Mpi allele frequencies for barnacles within the Gulf of St. Lawrence could be maintained by a combination of selection and limited gene flow from populations of S. balanoides on the Atlantic coast of Canada south of the Cabot Strait. We sampled S. balanoides from 19 sites in Greenland and Baffin Island, the Gulf of St. Lawrence, and on the Atlantic coasts of Nova Scotia and New Brunswick, Canada, in order to test these hypotheses. Presumptive genetic variation at 2 enzyme loci, Mpi and glucose-6-phosphate isomerase (Gpi ) , was quantified by isoelectric focusing. A11 populations were in Hardy-Weinberg equilibrium, and no Linkage disequilibrium between loci was observed. We found significant spatial variation in allele frequencies at both loci. In particular, S. balanoides populations within the Gulf of St. Lawrence were not genetically homogeneous at either locus. A discontinuity in allele frequencies at both the Gpj and Mpi loci occurred in the vicinity of the Mirarmchi estuary, in the southern Gulf. Comparisons of allele frequencies between barnacle recruits and adults suggested this population structure may have resulted from selection, in the case of Mpi, possibly associated with environmental temperature. Selection by ice scour does not appear to affect spatial variation in allele frequencies in the Gulf of St. Lawrence.

Microgeographic, Genetic and Morphological-Differentiation of Fresh-Water Snails - the Hydrobiidae of Wilson Promontory, Victoria, South-Eastern Australia

Population differentiation and speciation in freshwater snails in a small geographic area were investigated in a study of the morphology and genetics of 75 populations of hydrobiid snails from streams on Wilsons Promontory, Victoria, Australia. At least four genetically definable species occur in sympatry. One (Fluvidona recta sp. nov.) is genetically isolated from the others and the other three (of which only F: turbata sp. nov. is named) appear to be closely related and distinguished by a nearly fixed allozyme (MPI) difference. Heterozygote frequencies for the diagnostic Mpi locus fall well below Hardy-Weinberg expectations in zones of sympatry. There is significant population subdivision within at least two of the genetic species, but as the partitions are allopatric they are not categorised taxonomically. The situation may be explained by the divergence of upland and lowland populations when sea levels fell during the Pleistocene with subsequent secondary contact and low levels of hybridisation in the contact zones. Generally, there is very low gene flow between even closely adjacent populations and extremely low flow between different catchments, F-ST between populations within the same tributary ranging from 0.02 to 0.14 and within adjacent tributaries of the same catchment ranging from 0.03 to 0.59. Some correlations between allozyme data and measured environmental variables were observed but none of these were consistent over all taxa. Size (shell length) appears to be influenced by environment, but shell shape and the length of the opercular smear are more correlated with genetic patterns. A notable lack of correlation between anatomy and genetic groupings was found, although there was some with shell and opercular morphology. Two additional species (F: gippslandica, sp. nov. and F: foris, sp. nov.) from areas adjacent to the Promontory are used as outgroups.

Isoenzymatic diagnosis ofLitomosoides galizaiandLitomosoides sigmodontis

The morphological diagnosis of the two species, Litomosoides sigmodontis Chandler, 1931 and L. galizai Bain, Petit et Diagne, 1989 is confirmed by the isoenzymatic analysis. In L. galizai, the mannose-phosphate isomerase and the glucose-phosphate isomerase migrate much faster and therefore further than in L. sigmodontis ; a polymorphism at MPI locus is shown in L. sigmodontis that does not exist in L. galizai. The « L.? » line, derived from the meriones in which it and L. sigmodontis coexisted, is of the pure sigmodontis type, both in morphology and in isoenzymes.

Synteny mapping of the bovine IGHG2, CRC and IGF1 genes

A panel of bovine‐murine hybrid cell lines was analysed for 10 loci, including three (IGF1, IGHG2 and the calcium release channel gene [CRC]) that have previously been mapped in man, but not in cattle. The IGF and CRC genes were indirectly mapped to chromosomes 5 and 18 respectively and the syntenies of the HOX2 and GH genes and of the NP and FOS genes were confirmed. The results also show that the IGHG2 locus, which is linked to NP and FOS on human chromosome 14, is separated from these genes in cattle. By showing synteny of the IGHG2 and MPI loci, the IGHG2 locus has been indirectly mapped to chromosome 21.

Spatial and temporal differentiation in colonizing populations of Ceratitis capitata

Two ancestral populations (Kenya and Reunion), two Mediterranean (Procida and Sardinia) and one new American population (Guatemala) of Ceratitis capitata were examined by electrophoresis for genetic variability at 27 enzyme loci. Two ordination approaches (principal component analysis and a tree representation) and F-statistical analysis have been used to distinguish the various patterns of genetic variations and to infer the underline causes and their relative contribution to the total variation. Three main patterns of variation emerge from the data: geographical, annual and seasonal differentiation. A main part of intraspecific variability involves the differentiation of central (Kenya and Reunion) versus peripheral populations (the Mediterranean and the American populations). The analysis suggests that the genetic structure of these populations is correlated with the historical events of their colonization. The affinity of the Guatemalan population with the Kenyan one could be the result of a recent founding of this population from the source area (Africa). More ancient historical events of colonization characterize the two Mediterranean populations. Seasonal variation has been found in the Procida population and chiefly involves the Mpi locus. In the same population the genetic variation across years has a minimum in 1986 due to the release of sterile T-101 males.

Synteny mapping of the bovine IGHG2, CRC and IGF1 genes

A panel of bovine-murine hybrid cell lines was analysed for 10 loci, including three (IGF1, IGHG2 and the calcium release channel gene [CRC]) that have previously been mapped in man, but not in cattle. The IGF and CRC genes were indirectly mapped to chromosomes 5 and 18 respectively and the syntenies of the HOX2 and GH genes and of the NP and FOS genes were confirmed. The results also show that the IGHG2 locus, which is linked to NP and FOS on human chromosome 14, is separated from these genes in cattle. By showing synteny of the IGHG2 and MPI loci, the IGHG2 locus has been indirectly mapped to chromosome 21.

Contrasting amounts of geographical variation as evidence for direct selection: the Mpi and Pgm loci in eight crustacean species

At the Mpi locus in the amphipods Hyale plumulosa and Orchestia grillus, one allele in each species is less common inside six small bays on Long Island, New York, when compared with nearby exposed habitats on Long Island Sound. These consistently repeated differences in allele frequency could result from selection on the Mpi locus itself, or from selection on loci in linkage disequilibrium with Mpi. When one exposed and one protected site were compared in H. plumulosa, O. grillus, and six other peracarid crustacean species, the Mpi locus exhibited greater between-site variation than the Pgm locus in all eight species. The consistently greater geographical variation in Mpi is unlikely to result from selection on linked loci, and indicates that selection results directly from the Mpi polymorphisms.

Genetic polymorphism of adenosine deaminase and mannose phosphate isomerase in blood of arctic foxes, Alopex lagopus

Blood samples of 70 foxes, including 10 families, have been investigated by horizontal starch gel electrophoresis for the enzymes adenosine deaminase (ADA) and mannose phosphate isomerase (MPI). The observed variation of the enzymes could be explained as a result of one locus with two codominant alleles and one with three respectively. The segregation in the families of the alleles assumed for the two loci is in accordance with this genetic model. The frequency of the two alleles at the Ada locus is about the same and the slowest anodic migrating allele at the Mpi locus is the most frequent.