Estimation and adjustment of microsatellite null alleles in nonequilibrium populations

Nonamplified (null) alleles are a common feature of microsatellite genotyping and can bias estimates of allele and genotype frequencies, thereby hindering population genetic analyses. The frequency of microsatellite null alleles in diploid populations can be estimated for populations that are in Hardy–Weinberg equilibrium. However, many microsatellite data sets are from nonequilibrium populations, often with known inbreeding coefficients (F) or fixation indices (F_IS or F_ST). Here, we propose a novel null allele estimator that can be used to estimate the null allele frequency and adjust visible allele frequencies in populations for which independent estimates of F, F_IS or F_ST are available. The algorithm is currently available as an Excel macro that can be downloaded at no cost from http://www.microchecker.hull.ac.uk/ and will be incorporated into the software micro ‐checker .     

Polymorphism of hordein-coding loci in barley (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.) populations of Iran and Central Asian countries

Starch gel electrophoresis was performed to study polymorphism of hordeins encoded by the Hrd A, Hrd B, and Hrd F loci in 366 local old barley accessions from Iran and Central Asian countries, including Turkmenistan, Uzbekistan, Tajikistan (Mountain Badahsan), and Kirgizia. In total, 60 alleles with frequencies of 0.0003–0.2818 were observed for the Hrd A locus, 106 alleles with frequencies of 0.0003–0.1603 were observed for the Hrd B locus, and five alleles with frequencies of 0.0164–0.4131 were observed for the Hrd F locus. The alleles and allele frequencies displayed irregular distributions in barley populations of the above countries. Cluster analysis of the matrix of allele frequencies in populations from known collection sites revealed a cluster structure of local barley populations within each country. Local populations formed five differently sized clusters in Iran, six in Turkmenistan, three in Uzbekistan, and three in Kirgizia. The variation and allele frequency distribution of the hordein-coding loci in Iran and Central Asian countries were assumed to result from the introduction and spreading of barley forms via migrations of husbandmen.     

Measures of gene flow in the Columbian ground squirrel

From analyses of published data and a review of the literature, I studied indirect and direct measures of gene flow among populations of Columbian ground squirrels, Spermophilus columbianus. New analyses were used to examine an allozyme data set (seven polymorphic loci) that had been collected by Zammuto and Millar (1985a) from six populations of ground squirrels that were spread over 183 km. G-tests indicated significant variation in allele frequencies among populations, but F-statistics revealed relatively little population differentiation (average F _ST=0.026). F _ST values were used to estimate rates of gene flow indirectly and indicated fairly high rates of gene flow (average N _e m=13.5). Recorded dispersal distances of individual ground squirrels were fairly short (most<4 km, maximum recorded distance was 8.5 km), and the minimum distance between populations used to create the allozyme data set was about 25 km. Thus, direct dispersal among the populations in the allozyme data set was highly unlikely. Small genetically effective populations may have experienced high rates of migration over short distances (about 43% of adults in local populations were immigrants), however, resulting in homogeneous allele frequencies over the geographic range. This explanation provides an alternative to invoking gene flow in the recent past to explain discrepancies between dispersal distances in the field and homogenization of allele frequencies over large ranges, Mammalian species that have virtually complete dispersal of subadult males from the natal area might be expected to exhibit relatively high rates of gene flow, regardless of actual dispersal distances. Genetically effective populations may be much smaller than more extensive ecological populations and experience higher rates of gene flow.     

The distribution of Gc subtypes among the Mongoloid populations

The polymorphism of Gc (group-specific components) has been investigated for a series of 3,160 individual samples from 11 Mongoloid populations in Asia and North and South America by isoelectric focusing on polyacrylamide gels. The samples fall into six Gc phenotypes which can be explained by the three common alleles, Gc^1F, Gc^1S, and Gc², together with several variant phenotypes explained as the heterozygotes for the three common alleles. The distribution of Gc^1F suballele appears to be considerably different from population to population among Mongoloids, ranging from 0.105 (Machiguenga Indans, Peru) to 0.609 (Kadazan, Borneo). A clear geographic cline from Southeast Asia into South America in Gc^1F allele was observed in the populations. In general, Gc^1F allele frequencies are lower in European populations and higher in African populations. The range of variability in the Gc^1F values observed among the Asiatic populations is between the Africans and the Europeans.     

Allozyme variation in Greek wild populations of Drosophila melanogaster and D. simulans along a North-South gradient

Allozyme frequency data from five Greek wild sympatric populations of Drosophila melanogaster and D. simulans along a North-South gradient were analyzed for genotype-environment relationships. The regression coefficient of genetic distance on geographic distance indicates that there is a significant relationship between these parameters for D. melanogaster only. Highly significant differences in specific alleles at certain loci were found between the various local populations studied. The changes in Gpdh ^F of D. melanogaster and Est-6 ^F of D. simulans exhibited clinal patterns in allele frequencies. In addition, analysis of D. melanogaster Gpdh ^Fand Adh ^F allele frequencies shows that the Greek data do not have regression coefficients (regressing allele frequency on degrees North of latitude) of the same sign as East-and West-Coast United-States populations. These contradictory data are discussed in relation to what is known about the maintenance of the Adh and Gpdh polymorphisms.     

Frequency of alleles conferring resistance to Bacillus thuringiensis maize in Louisiana populations of the southwestern corn borer

Transgenic maize [Zea mays L. (Poaceae)] expressing Bacillus thuringiensis proteins (Bt maize) has become the most important tool for managing stalk borers in maize in the USA. The current strategy for delaying the evolution of resistance in target insects for Bt maize is referred to as high dose/refuge strategy. A key requirement of the strategy is that initial resistance allele frequencies in field insect populations are low (e.g., <0.001). More than 200 iso‐line families of the southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), a major target stalk borer pest of Bt maize, were developed from Louisiana populations and evaluated for Bt resistance using a modified F₂ screening method during 2005. No major resistance alleles were detected in these populations. The results showed that the expected Bt resistance allele frequency in the Louisiana populations was <0.0035 with 95% probability and a detection power of 83.9 ± 0.6%. The F₂ screen indicates that Bt resistance allele frequencies in D. grandiosella are low among the Louisiana populations and should meet the rare resistance allele requirement of the ‘high dose/refuge’ strategy.     

Testing transposable elements as genetic drive mechanisms using Drosophila P element constructs as a model system

The use of transposable elements (TEs) as genetic drive mechanisms was explored using Drosophila melanogaster as a model system. Alternative strategies, employing autonomous and nonautonomous P element constructs were compared for their efficiency in driving the ry⁺ allele into populations homozygous for a ry^- allele at the genomic rosy locus. Transformed flies were introduced at 1%, 5%, and 10% starting frequencies to establish a series of populations that were monitored over the course of 40 generations, using both phenotypic and molecular assays. The transposon-borne ry⁺ marker allele spread rapidly in almost all populations when introduced at 5% and 10% seed frequencies, but 1% introductions frequently failed to become established. A similar initial rapid increase in frequency of the ry⁺ transposon occurred in several control populations lacking a source of transposase. Constructs carrying ry⁺ markers also increased to moderate frequencies in the absence of selection on the marker. The results of Southern and in situ hybridization studies indicated a strong inverse relationship between the degree of conservation of construct integrity and transposition frequency. These finding have relevance to possible future applications of transposons as genetic drive mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Population genetics of the metabolically related Adh,Gpdh and Tpi polymorphisms in Drosophila melanogaster I. Geographic variation in Gpdh and Tpi allele frequencies in different continents

Among Australasian populations from above 32.5° latitude there is a significant negative relationship between Gpdh ^F frequency and distance from the equator which is not explained by gametic disequilibrium with the linked inversion In(2L)t. This is consistent with the associations reported earlier for Gpdh ^F among populations covering comparable latitudes in North America and Europe/Asia. By contrast, Tpi allele frequencies are found to be significantly associated with distance from the equator in Australasia but not North America or Europe/Asia. The Tpi pattern in the different zones is essentially the same as that reported earlier for the Acph polymorphism, which maps only 0.2 cM away from the Tpi locus.There are now ten enzyme polymorphisms in D. melanogaster which have been screened for latitudinal associations in Australasia, North America and Europe/Asia. Allele frequencies at six of these loci show significant relationships with distance from the equator which are consistent across all three zones. These latitudinal associations are more prevalent for Group II than Group I enzymes. Values of genic heterozygosity averaged over the ten polymorphic loci and eleven other monomorphic systems do not vary with latitude but differ substantially between zones. Values of Nei's genetic distance between North American and European/Asian populations calculated from all 21 systems are equivalent to subspecific differences elsewhere in the genus.     

REGIONAL,LOCAL AND MICROGEOGRAPHIC ALLELE FREQUENCY VARIATION BETWEEN APPLE AND HAWTHORN POPULATIONS OF RHAGOLETIS POMONELLA IN WESTERN MICHIGAN

In the preceding study (Feder et al., 1990), we report that paired apple and hawthorn infesting populations of Rhagoletis pomonella are genetically differentiated for six allozymes. Here, we show that patterns of intra- and inter-host allele frequency variation seen for these six loci across the eastern United States are consistent on a more fine grained spatial scale in western Michigan. Malic enzyme, Aconitase-2, Mannose phosphate isomerase, and Hydroxyacid dehydrogenase all displayed significant linear relationships with latitude among five “regional” hawthorn populations sampled along a north-south transect between the cities of Cadillac and Portage, Michigan. Clines were not as evident among “regional” apple populations in western Michigan, although allele frequencies for Malic enzyme¹⁰⁰, Mannose phosphate isomerase¹⁰⁰ and Aconitase-2⁹⁵ varied with latitude among six “local” apple populations within a 60 km² area near the town of Grant. Significant allele frequency differences were observed between hawthorn and apple populations at all “regional” and “local” collecting sites analyzed in the study (a total of 20 different apple and hawthorn populations). As was the case in the geographic survey of the eastern United States, the magnitude and pattern of inter-host frequency differences at “regional” and “local” sites were a function of latitude. Host related genetic differentiation was consistent on a “microgeographic” scale as well. Allele frequencies for Malic enzyme¹⁰⁰ and Aconitase-2⁹⁵ were significantly higher over a four-year period (1984 to 1987) for flies sampled from individual hawthorn trees (N = 6) than apple trees (N = 7) within an old field (0.09-km² area) located near Grant. The fine level of genetic subdivision between hawthorn and apple populations of R. pomonella in western Michigan substantiates the existence of host associated polymorphism in the fly and supports a sympatric mode of divergence for the “apple race”.     

Pedigreed crosses to estimate recessive virulence allele frequencies in natural populations of gall midges

Monitoring changes in rare, recessive allele frequencies in natural populations can be accomplished using pedigreed individuals sampled from these populations. A pedigree keeps track of and limits the mating of sampled individuals, to preserve information about the genotype of the sampled individual in the phenotypes of its descendents. To estimate allele frequencies in a natural population using pedigreed crosses, four relations must be specified: (1) a method to determine whether the pedigreed line carries the desired allele; (2) a method to estimate the phenotypic frequency of the trait among the pedigreed lines and a credibility limit for the estimate; (3) the genetic relation between the phenotype frequency among the lines and the allele frequency in the natural population; and (4) a method to estimate the probability that the first method did not detect the trait, assuming that the allele was present in the sampled individual. Knowledge about the segregation patterns of the allele enables specification of (3) and (4). Bayesian statistics were used to estimate the phenotypic frequency of the trait among the pedigreed lines. The method determining whether the pedigreed line carries the desired allele will vary with the species and trait of concern. We focused on monitoring of vGm1, a recessive autosomal allele, and vGm2, a recessive sex‐linked allele, which provide virulence against certain rice resistance genes in rice gall midge, Orseolia oryzae (Wood‐Mason) (Diptera: Cecidomyiidae). We show how three pedigrees can be used to estimate these allele frequencies. An F₁ field screen challenges the F₁ offspring of sampled individuals on the rice differentials. A P₁ test‐cross mates the sampled individual with a homozygous lab colony for the allele of interest, and evaluates their offspring on the rice differentials. A conditional F₁ test‐cross takes the offspring from pedigrees that were negative in an F₁ field screen, and test‐crosses these offspring with the homozygous laboratory colony. We also indicate how to test for independent assortment when a double (or multiple) homozygote laboratory colony is used in a test‐cross, how to test for differences among samples, and how to pool data to produce a single estimate based on a larger number of pedigreed lines. These methods may encourage the development of a variety of pedigreed monitoring strategies that could improve and prolong the use of scarce plant resistance alleles in rice and other plants.     

Latitudinal Adh allozymic variation and ethanol tolerance in Indian populations of Drosophila melanogaster

Ten Indian geographical populations of D. melanogaster were assayed electrophoretically for Adh genic variation. The Indian geographical populations of D. melanogaster revealed significant clinal variation (3 % for 1 d? latitude) at Adh locus and Adh^F allelic frequency correlated significantly with increase in latitude. It was suggested that the abundance of secondary alcohols in the southern Indian tropical and humid environment might exert selective pressure favouring higher frequency of Adh^S allele. Patterns of ethanol utilization as well as ethanol tolerance were analyzed in larval and adult individuals of six geographical populations of D. melanogaster. Latitudinal variation in ethanol tolerance was observed in D. melanogaster populations from India. The parallel occurrence of latitudinal variation it Adh locus as well as ethanol tolerance in Indian geographical populations of D. melanogaster could be maintained by balancing natural selection varying spatially along the north-south axis of the Indian sub-continent.     

The Dagestan gene pool: Polymorphism of immunogenetic and biochemical markers in Kumyks

This study is a part of long-term investigations devoted to the analysis of the gene pool of Dagestan ethnic groups. The phenotype (in %), gene, and haplotype frequencies in Kumyk ethnic group are reported. A total of 39 alleles and six haplotypes of 14 loci (AB0, Rhesus, P, Levis, Kell, HP, GC, C’3, TF, 6PGD, GLO1, ESD, ACP, and PGM1) of immunobiochemical genetic marker systems were examined. Rare haplotypes of the Rhesus system were identified, including CDE in the Karabudakhkent population with the frequency of 0.030, and Cde and cdE in the Dorgeli population with the frequencies of 0.034 and 0.38, respectively. Similarly to the other ethnic populations of Dagestan examined, Kukyk populations carried rare, albeit typically “Caucasoid” gene ACP1 ^c of the AcP1 locus. The frequency of this allele in the two populations was similar, constituting 0.031 for Karabudakhkent and 0.032 for Dorgeli. In Kumyks, allele frequencies of the AB0, Rhesus, P, Lewis, Kell, HP, GC, C′3, TF, 6PGD, GLO1, ESD, ACP, but not PGM1, systems were similar to the mean allele frequencies at these loci observed in the other ethnic groups from the Dagestan, Caucasus, and the whole European historical ethnographic province. At the same time, the allele frequency values obtained were different from those for the populations of Kazakhstan, Central Asia, Siberia, and the Ruswsian Far East. Thus, the results obtained for classical genetic markers indicate that Kumyks are genetically closer to the indigenous populations of Dagestan than to Turkic-speaking populations. Analysis of the fit of the observed phenotype frequencies to the Hardy-Weinberg expectations showed that compared to other indigenous populations of Dagestan examined, in Kumyks the genetic state of the population upon random allele association was close to equilibrium. Probably, this state was determined by practical absence of the consanguineous marriages upon preservation of intra-aul endogamy.     

Population Structure of the Giant Garter Snake, Thamnophis gigas

The giant garter snake, Thamnophis gigas, is a threatened species endemic to California’s Central Valley. We tested the hypothesis that current watershed boundaries have caused genetic differentiation among populations of T. gigas. We sampled 14 populations throughout the current geographic range of T. gigas and amplified 859 bp from the mitochondrial gene ND4 and one nuclear microsatellite locus. DNA sequence variation from the mitochondrial gene indicates there is some genetic structuring of the populations, with high F_ST values and unique haplotypes occurring at high frequency in several populations. We found that clustering populations by watershed boundary results in significant between-region genetic variance for mtDNA. However, analysis of allele frequencies at the microsatellite locus NSU3 reveals very low F_ST values and little between-region variation in allele frequencies. The discordance found between mitochondrial and microsatellite data may be explained by aspects of molecular evolution and/or T. gigas life history characteristics. Differences in effective population size between mitochondrial and nuclear DNA, or male-biased gene flow, result in a lower migration rate of mitochondrial haplotypes relative to nuclear alleles. However, we cannot exclude homoplasy as one explanation for homogeneity found for the single microsatellite locus. The mitochondrial nucleotide sequence data supports conservation practices that identify separate management units for T. gigas.     

Empirical Distributions of F ST from Large-Scale Human Polymorphism Data

Studies of the apportionment of human genetic variation have long established that most human variation is within population groups and that the additional variation between population groups is small but greatest when comparing different continental populations. These studies often used Wright’s F _ST that apportions the standardized variance in allele frequencies within and between population groups. Because local adaptations increase population differentiation, high-F _ST may be found at closely linked loci under selection and used to identify genes undergoing directional or heterotic selection. We re-examined these processes using HapMap data. We analyzed 3 million SNPs on 602 samples from eight worldwide populations and a consensus subset of 1 million SNPs found in all populations. We identified four major features of the data: First, a hierarchically F _ST analysis showed that only a paucity (12%) of the total genetic variation is distributed between continental populations and even a lesser genetic variation (1%) is found between intra-continental populations. Second, the global F _ST distribution closely follows an exponential distribution. Third, although the overall F _ST distribution is similarly shaped (inverse J), F _ST distributions varies markedly by allele frequency when divided into non-overlapping groups by allele frequency range. Because the mean allele frequency is a crude indicator of allele age, these distributions mark the time-dependent change in genetic differentiation. Finally, the change in mean-F _ST of these groups is linear in allele frequency. These results suggest that investigating the extremes of the F _ST distribution for each allele frequency group is more efficient for detecting selection. Consequently, we demonstrate that such extreme SNPs are more clustered along the chromosomes than expected from linkage disequilibrium for each allele frequency group. These genomic regions are therefore likely candidates for natural selection.     

Population genetic studies of the crown-of-thorns starfish,Acanthaster planci (L.), in the Great Barrier Reef region

Seven populations of the crown-of-thorns starfish, Acanthaster planci, were compared genetically using starch gel electrophoresis in order to investigate the extent of genetic exchange throughout the Great Barrier Reef (GBR) region. These populations extended from Lizard Island in the north to One Tree Island in the south, a distance of approximately 1300 km. Thirteen of 36 enzymes assayed were genetically interpretable, and 10 (77%) of these were polymorphic. Mean heterozygosity over all loci was 0.225. An analysis of the gene frequency heterogeneity between the populations using Wright's F _ST statistic gave an overall F _ST of 0.019. The mean unbiased value of Nei's genetic distance between the populations was 0.009. These values indicate a homogeneous genetic composition throughout the range, and are consistent with the hypothesis that gene flow between these populations is high, and that A. planci throughout the GBR region are members of a single, effectively panmictic population. Within this group, the Green Island population was most distinct genetically because of differences in allele frequencies at the MDH-1 locus. Although there is no rigorous method for determining the selective basis for such differences, it is argued that the differences observed in the Green Island population were the result of selection. The basis for selective differences was possibly food availability since, at the time of sampling, the Green Island A. planci were the remnants of a large, high-density population that caused extensive coral mortality, and suffered severe population decline as food became scarce. These findings are consistent with observations of a relatively ordered sequence of outbreaks from north to south along the GBR, suggesting that all outbreaks but the first are secondary. Control measures, both on the GBR and elsewhere, have been unsuccessful except on a very small scale. Unless a vulnerable part of the A. planci life cycle can be identified, it would seem that the greatest chance for successful control would be to identify and control the causes of the primary population outbreak.     

Population estimators or progeny tests: what is the best method to assess null allele frequencies at SSR loci?

Nuclear SSRs are notorious for having relatively high frequencies of null alleles, i.e. alleles that fail to amplify and are thus recessive and undetected in heterozygotes. In this paper, we compare two kinds of approaches for estimating null allele frequencies at seven nuclear microsatellite markers in three French Fagus sylvatica populations: (1) maximum likelihood methods that compare observed and expected homozygote frequencies in the population under the assumption of Hardy-Weinberg equilibrium and (2) direct null allele frequency estimates from progeny where parent genotypes are known. We show that null allele frequencies are high in F. sylvatica (7.0% on average with the population method, 5.1% with the progeny method), and that estimates are consistent between the two approaches, especially when the number of sampled maternal half-sib progeny arrays is large. With null allele frequencies ranging between 5% and 8% on average across loci, population genetic parameters such as genetic differentiation (F _ST) may be mostly unbiased. However, using markers with such average prevalence of null alleles (up to 15% for some loci) can be seriously misleading in fine scale population studies and parentage analysis.     

A long-term study on interactions between the Adh and αGpdh allozyme polymorphisms and the chromosomal inversion In(2L)t in a seminatural population of D. melanogaster

The Adh and αGpdh allozyme loci (both located on the second chromosome) showed considerable fluctuations in allele frequencies in a seminatural population of Drosophila melanogaster during 1972–97. Both long-term and short-term fluctuations were observed. The short-term fluctuations occurred within almost all years and comparison of allele frequencies between winters and summers showed significantly higher Adh^S (P < 0.001) and αGpdh^F (P < 0.01) allele frequencies in summers. Frequencies of these alleles were significantly positively correlated with environmental temperature, suggesting the adaptive significance of these allozyme polymorphisms. Frequency changes of the Odh locus (located on the third chromosome) showed no seasonal pattern and were not correlated with environmental temperature. Almost all short-term and long-term increases in Adh^S frequency were accompanied by a corresponding decrease in αGpdh^S frequency (r = –0.82, P < 0.001) and vice versa. Further analysis showed that gametic disequilibria between the Adh and αGpdh loci, which frequently occurred, were due to the presence of inversion In(2L)t located on the same chromosome arm and In(2L)t frequencies were positively correlated with environmental temperature. Gametic disequilibria between Adh and Odh and between Odh and αGpdh were hardly observed. Because In(2L)t is exclusively associated with the Adh^S/αGpdh^F allele combination, the observed correlated response in Adh/αGpdh allele frequencies is (at least partly) explained by hitchhiking effects with In(2L)t. This means that the adaptive value of the allozyme polymorphisms has been overestimated by ignoring In(2L)t polymorphism. Fluctuations in Adh allele frequencies are fully explained by selection on In(2L)t polymorphism, whereas we have shown that αGpdh frequency fluctuations are only partly explained by chromosomal hitchhiking, indicating the presence of selective differences among αGpdh genotypes in relation with temperature and independent of In(2L)t. Frequency fluctuations of αGpdh and In(2L)t are consistent with their latitudinal distributions, assuming that temperature is the main environmental factor varying with latitude that causes directly or indirectly these frequency distributions. However, the results of the tropical greenhouse population show no correlation of Adh (independent of In(2L)t) and Odh allele frequencies with environmental temperature, which may indicate that the latitudinal distribution in allele frequencies for these loci is not the result of selection on the F/S polymorphism in a direct way.     

Genetic consequences of introducing allopatric lineages of Bluestriped Snapper (Lutjanus kasmira) to Hawaii

A half century ago the State of Hawaii began a remarkable, if unintentional, experiment on the population genetics of introduced species, by releasing 2431 Bluestriped Snappers (Lutjanus kasmira) from the Marquesas Islands in 1958 and 728 conspecifics from the Society Islands in 1961. By 1992 L. kasmira had spread across the entire archipelago, including locations 2000 km from the release site. Genetic surveys of the source populations reveal diagnostic differences in the mtDNA control region (d = 3.8%; φ_ST = 0.734, P < 0.001) and significant allele frequency differences at nuclear DNA loci (F_ST = 0.49; P < 0.001). These findings, which indicate that source populations have been isolated for approximately half a million years, set the stage for a survey of the Hawaiian Archipelago (N = 385) to determine the success of these introductions in terms of genetic diversity and breeding behaviour. Both Marquesas and Society mtDNA lineages were detected at each survey site across the Hawaiian Archipelago, at about the same proportion or slightly less than the original 3.4:1 introduction ratio. Nuclear allele frequencies and parentage tests demonstrate that the two source populations are freely interbreeding. The introduction of 2431 Marquesan founders produced only a slight reduction in mtDNA diversity (17%), while the 728 Society founders produced a greater reduction in haplotype diversity (41%). We find no evidence of genetic bottlenecks between islands of the Hawaiian Archipelago, as expected under a stepping‐stone model of colonization, from the initial introduction site. This species rapidly colonized across 2000 km without loss of genetic diversity, illustrating the consequences of introducing highly dispersive marine species.     

Genetic studies of complement C4 in man

Summary A C4 variant found in about 5% of the population is described. The fast-moving part of this variant is governed by an allele (F ^x) codominant to F. The F ^x allele is in very strong linkage disequilibrium with HLA-B17 as the linkage disequilibrium parameter accounted for nearly 100% of the haplotype frequency of B17, F ^x. The strong association is also evidenced by the study of 11 families segregating for the F ^x allele. There was no instance of recombination between C4 and HLA in 36 informative meioses.     

Placental alkaline phosphatase polymorphism in some Italian populations

Summary Gene frequencies of Pl alleles for alkaline phosphatase of human placenta have been studied in the populations of Rome and L'Aquila. The latter represents a mixed sample of descendants from ancient Italic populations which in the last 20 centuries have been free from significant immigratory influx.The Pl gene frequencies in the two Italian populations are significantly different, the Pl ^s ₁ frequency being lower and Pl ^f ₁ frequency higher in the population of L'Aquila as compared to the population of Rome. The gene frequency of the 3 common Pl alleles in the population of Rome are quite similar to that found in some Northern-European populations. The frequency of the Pl ^s ₁ allele observed in the population of L'Aquila is the lowest (and correspondingly that for Pl ^f ₁ allele is the highest) amongst all populations studied so far.