Linkage disequilibrium at the ADH2 and ADH3 loci and risk of alcoholism

Two of the three class I alcohol dehydrogenase (ADH) genes (ADH2 and ADH3) encode known functional variants that act on alcohol with different efficiencies. Variants at both these genes have been implicated in alcoholism in some populations because allele frequencies differ between alcoholics and controls. Specifically, controls have higher frequencies of the variants with higher Vmax (ADH2*2 and ADH3*1). In samples both of alcoholics and of controls from three Taiwanese populations (Chinese, Ami, and Atayal) we found significant pairwise disequilibrium for all comparisons of the two functional polymorphisms and a third, presumably neutral, intronic polymorphism in ADH2. The class I ADH genes all lie within 80 kb on chromosome 4; thus, variants are not inherited independently, and haplotypes must be analyzed when evaluating the risk of alcoholism. In the Taiwanese Chinese we found that, only among those chromosomes containing the ADH3*1 variant (high Vmax), the proportions of chromosomes with ADH2*1 (low Vmax) and those with ADH2*2 (high Vmax) are significantly different between alcoholics and controls (P<10-5). The proportions of chromosomes with ADH3*1 and those with ADH3*2 are not significantly different between alcoholics and controls, on a constant ADH2 background (with ADH2*1, P=.83; with ADH2*2, P=.53). Thus, the observed differences in the frequency of the functional polymorphism at ADH3, between alcoholics and controls, can be accounted for by the disequilibrium with ADH2 in this population.     

The effect of mating system differences on nucleotide diversity at the phosphoglucose isomerase locus in the plant genus Leavenworthia.

To test the theoretical prediction that highly inbreeding populations should have low neutral genetic diversity relative to closely related outcrossing populations, we sequenced portions of the cytosolic phosphoglucose isomerase (PgiC) gene in the plant genus Leavenworthia, which includes both self-incompatible and inbreeding taxa. On the basis of sequences of intron 12 of this gene, the expected low diversity was seen in both populations of the selfers Leavenworthia uniflora and L. torulosa and in three highly inbreeding populations of L. crassa, while high diversity was found in self-incompatible L. stylosa, and moderate diversity in L. crassa populations with partial or complete self-incompatibility. In L. stylosa, the nucleotide diversity was strongly structured into three haplotypic classes, differing by several insertion/deletion sequences, with linkage disequilibrium between sequences of the three types in intron 12, but not in the adjacent regions. Differences between the three kinds of haplotypes are larger than between sequences of this gene region from different species. The haplotype divergence suggests the presence of a balanced polymorphism at this locus, possibly predating the split between L. stylosa and its two inbreeding sister taxa, L. uniflora and L. torulosa. It is therefore difficult to distinguish between different potential causes of the much lower sequence diversity at this locus in inbreeding than outcrossing populations. Selective sweeps during the evolution of these populations are possible, or background selection, or merely loss of a balanced polymorphism maintained by overdominance in the populations that evolved high selfing rates.     

Allelic diversity at the Mhc-DQA locus of woodmouse populations (Apodemus sylvaticus) present in the islands and mainland of the northern Mediterranean

Aim Polymorphism at neutral markers and at MHC loci in rodent populations living on islands is generally low. The main genetic factors that may contribute to a reduced level of genetic variability are genetic drift, reduced gene flow and founder events. We investigated the pattern of polymorphism at the second exon of the Mhc‐DQA gene in island populations of Apodemus sylvaticus and in their mainland counterparts to investigate the pattern of MHC polymorphism in a phylogeographical context and to assess the impact of insularity on diversity at this locus. Location Eight north Mediterranean populations of Apodemus sylvaticus were studied, including five island populations (Majorca, Minorca, Porquerolles, Port‐Cros and Sicily) and three mainland populations. Methods cDNA sequencing and nucleotide sequences analyses. Synonymous and non‐synonymous substitutions were examined at the PBR and non‐PBR sites. The DQA allelic distribution in populations was compared with the woodmouse phylogeography. Results This study presents novel DQA alleles. High polymorphism of the DQA locus is recorded in natural populations of A. sylvaticus with 13 alleles being widely distributed irrespective of the geographical origin and palaeoclimatic history of populations. The DQA locus does not show the expected pattern for non‐synonymous substitutions at the PBR sites. However, island populations show a weak loss of polymorphism in comparison with their mainland counterparts. Main conclusions The DQA locus in the woodmouse seems to be subject to weak selection and does not allow resolution of phylogeographical relationships among European woodmouse populations. The presence of at least three alleles in island populations and the maintenance of five alleles between the two European lineages over 1.5 Myr suggest that balancing selection may act within populations, and more precisely within island populations, to maintain genetic variability. This study shows that phylogeographical studies are a prerequisite for any genetic investigation of selected genes in natural populations.     

三个虹鳟养殖群体遗传结构的微卫星分析

利用20个微卫星标记对3个虹鳟(Oncorhynchus mykiss)养殖群体进行遗传结构分析。结果表明,(1)3个群体检测的平均等位基因数为3·6～4·1,平均观测杂合度为0·5224～0·6328,平均期望杂合度为0·4736～0·5522,平均多态信息含量为0·4354～0·5084,说明这几个群体多态性属于偏高水平,遗传多样性高。通过d值,确定了Hard-Weinberg平衡的偏离情况,发现AY039638、AY039646在3个群体中都表现为不平衡。对3个群体的遗传距离进行了估算,并进行聚类分析,本溪的两个群体先聚为一支,再与渤海群体相聚,显示出明显的地理特征。(2)本溪虹鳟群体在位点AF352770出现部分等位基因消失的现象;AF352754在本溪群体中表现为位点消失,可作为区分本溪群体和渤海群体的分子标记。(3)综合评价3个群体,渤海站虹鳟群体的遗传多样性最高,与前人研究结果一致。     

Heterozygote deficiencies in small lacustrine populations of brook charr Salvelinus Fontinalis Mitchill (Pisces,Salmonidae): a test of alternative hypotheses

Empirical studies of natural populations have commonly reported departures from Hardy-Weinberg expected proportions of heterozygote individuals. Recent advances in statistical population genetics now offer the potential to exploit individual multilocus genotypic information to test more rigorously for possible sources of heterozygote deficiencies. In a previous study in lacustrine brook charr (Salvelinus fontinalis), we reported stronger deficits in small than in large lakes. In the present paper, we propose a methodology for empirically testing alternative hypotheses to identify the cause of the deficits observed in three of the smallest lakes (85, 109 and 182 ha) analysed. First, as in several salmonid species, brook charr may exhibit a trophic polymorphism in north temperate lakes. If morphs are genetically divergent, indiscriminate sampling of both forms would result in less heterozygote individuals than expected in a randomly mating population (Wahlund effect). Using an individual-based method aiming at detecting cryptic population structure, we can reject this explanation as the sole source of deficits for all three lakes. Secondly, mating among relatives could also be frequent in small lakes and lead to heterozygote deficiencies. Significantly more fish than expected at random had low individual multilocus heterozygosity in two of the lakes, suggesting that inbred fish may have been present. Thirdly, sampling of genetically related fish would also lead to departures from Hardy-Weinberg proportions. In the same two lakes, the distribution of pairwise relatedness coefficients departed from its random expectation, suggesting that non-random sampling of kin may have occurred.     

Relationship between Migration and DNA Polymorphism in a Local Population

The expected amount of DNA polymorphism, measured in terms of the number of nucleotide differences between the two DNA sequences randomly sampled from subpopulations, was studied by using the stepping-stone model and the finite island model, under the assumption that the migration rate is not the same among different subpopulations. The results obtained indicate that the expected amount of DNA polymorphism in the subpopulation with lower migration rate is smaller than that of higher migration rate. This suggests that marginal populations tend to have lower level of DNA polymorphism than central populations if the migration rate in the marginal populations is lower than that of the central populations.     

Genetic load and coadaptation of chromosomal inversions. II. O-chromosomes in Drosophila subobscura populations

We have analysed the inversion polymorphism and genetic load of O-chromosomes in three populations of D. subobscura from southeastern Europe. As expected for a central populations the inversion polymorphism was extensive. In a like fashion, the genetic load, in particular the frequency of lethals, was heavy in all three populations. There were significant differences in the frequency of moderately deleterious genes. These differences in viability can be attributed to balancing selection. A comparison of these two kinds of genetic polymorphism indicates that there are differences in mean viability among different gene arrangements of O-chromosomes in the three populations. The differences observed are due to an unequal distribution of various viability classes among O-chromosome gene arrangements. We here show for the first time a specific distribution of lethal genes among these arrangements within the Palearctic distribution area of D. subobscura. The lethal allelism test showed lethals are non-randomly associated with the Ost gene arrangement. The amount of genetic load is heavy in gene arrangements with a high frequency, in comparison with the ones with a low frequency. Lethal genes may be protected in combinations of low and moderate frequency gene arrangements that harbor more lethal genes, as the Ost in the one population. Some arrangements that are less protected against recombination have a higher load than ones that are more protected against recombination. This can be taken as evidence for coadaptation.     

Long-term occurrence of hybrids between Japan Sea and Pacific Ocean forms of threespine stickleback, <Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis>, in Hokkaido Island,Japan

The distribution patterns of two genetically divergent forms (Japan Sea and Pacific Ocean forms) of Gasterosteus aculeatus and their hybrids in the Hokkaido Island, Japan were investigated. Hybrid frequencies and the mating pattern of natural F1-hybrids and backcrosses, were examined by using allozyme analysis. The distribution patterns matched those previously reported. All three sympatric localities in eastern Hokkaido Island included hybrids between the two forms in each year examined. A low frequency of hybrids of sticklebacks has been maintained in areas of sympatry of the two forms in Hokkaido Island for several years. The proportion of F1-hybrids was significantly lower than expected by random mating in six samples from four sympatric populations, suggesting form-assortative mating. Mating crosses of natural F1-hybrids existed in both patterns. Natural F1-hybrids backcrossed more frequently with Pacific Ocean form than Japan Sea form. However, the proportions of backcross individuals in two of three samples were not significantly different from the expected proportions by random mating between F1-hybrids and their parent forms. In other samples, despite the Pacific Ocean form predominant in a population, F1-hybrid predominantly backcrossed with the Japan Sea form. These results support the hypothesis of gene flow from Pacific Ocean to Japan Sea forms.     

Isolation of 10 tetranucleotide microsatellite loci in the blackcap (Sylvia atricapilla)

We isolated 10 polymorphic microsatellite DNA loci from the blackcap (Sylvia atricapilla) and optimized them for future studies of population differentiation in populations with different migration strategies in southwestern Germany. The loci were screened for polymorphism using 178 individuals from two populations in Germany and Spain. The primers amplified highly variable loci characterized by two to 19 alleles per locus and their observed and expected heterozygosities range from 0.47 to 0.81 and from 0.50 to 0.91, respectively.     

Chromosomal variability in natural populations of Chironomus cingulatus meigen (Diptera, Chironomidae)

Chromosomal polymorphism has been studied in seven natural populations of Chironomus cingulatus from Western Europe, Western Siberia, and the Republic of Sakha (Yakutia). The banding sequences pool of the species includes 15 banding sequences. Chromosomal polymorphism was revealed in five out of seven chromosomal arms. Arm B is the most polymorphic with four banding sequences. There are three banding sequences in arm A. Arms D, E, and G have two banding sequences. None of the chromosome rearrangements were revealed in arms C and F. The populations of C. cingulatus differ clearly in their number and frequency of banding sequences, which indicates that different gene sequences are adaptive in different populations.     

Genetic differentiation among local populations of the European hedgehog (Erinaceus europaeus) in mosaic habitats

Tissue samples from 160 European hedgehogs, Erinaceus europaeus , representing eight small populations from a highly fragmented landscape in Oxfordshire, UK, were screened for polymorphism at six microsatellite loci. Permutation analysis of allelic compositions revealed no evidence for linkage disequilibrium among loci. Genotype proportions within populations and at five loci did not differ from those expected at Hardy–Weinberg equilibrium. However, significant heterozygote deficit and amplification failure of several samples necessitated removal of one locus from the analysis. Mean observed heterozygosity was 0.70. Average Rho _ST was 0.079 and differed significantly from zero, suggesting restricted gene flow among local populations. Pairwise Nm values and geographical distance were not correlated, indicating that factors other than distance affected dispersal.     

Population genetics of Drosophila ananassae: genetic differentiation among Indian natural populations at the level of inversion polymorphism

The present study, which is one of the longest temporal (two decades) and largest spatial (different parts of India covered) investigations on inversion polymorphism in natural populations of D. ananassae, was undertaken to understand the dynamics of inversion polymorphism in a broad and comprehensive manner. Forty-five natural populations from different ecogeographic regions of the country (covering the regions from Kashmir to Kanniyakumari and Gujarat to Nagaland) were analysed for chromosomal inversions. All the populations show the presence of the three cosmopolitan inversions, frequencies of which vary among the populations analysed. Simple correlations between frequencies of different inversions and regression analysis of inversion frequencies with latitude, longitude and altitude were insignificant. This reinforces the concept of rigid polymorphism in D. ananassae. Genetic divergence (spatial and temporal) at the level of chromosomal polymorphism among natural populations was calculated. Results show spatial divergence but no temporal divergence. Rigid polymorphic systems of D. ananassae did not show long-term directional trends. On the basis of the present study, and after including comparisons with the studies conducted more than two decades ago, the most important conclusion to be drawn is that the three cosmopolitan inversions in D. ananassae segregate within populations at fairly similar frequencies, and the general geographic pattern has remained constant.     

长喙毛茛泽泻遗传多样性及其与繁育系统的关系

利用聚丙烯酰胺凝胶电泳技术测定了濒危植物长喙毛茛泽泻（ＲａｎａｌｉｓｍａｒｏｓｔｒａｔｕｍＳｔａｐｆ）及３个对照种冠果草［Ｓａｇｉｔａｒｉａｇｕａｙａｎｅｎｓｉｓｓｓｐｌａｐｐｕｌａ（ＤＤｏｎ）Ｂｏｇｉｎ］、武夷慈姑（ＳｗｕｙｉｅｎｓｉｓＪＫＣｈｅｎｅｔａｌ）、矮慈姑（ＳｐｙｇｍａｅａＭｉｑ）共６个自然居群的遗传多样性。自花受精和以营养繁殖为主的长喙毛茛泽泻维持较低的遗传多样性,预期杂合度和观察杂合度分别为００６４和０１０４。以自花受精为主的冠果草遗传多样性更低,预期杂合度和观察杂合度分别为００３９和００６７。异体繁育但以营养繁殖为主的武夷慈姑遗传多样性比长喙毛茛泽泻的高,预期杂合度和观察杂合度分别为０１１１和０１８３。以异体繁育为主和营养繁殖的矮慈姑遗传多样性在这４个种中最高,其预期杂合度和观察杂合度分别是０１５５和０２６９。４个种的内繁育系数Ｆ值全为负值。冠果草、长喙毛茛泽泻、武夷慈姑直至矮慈姑,其异交程度从几乎为零逐渐递增,而其遗传多样性指标也相应地增高。长喙毛茛泽泻的遗传多样性程度高于冠果草但冠果草并不濒危,因此遗传多样性较低并不是濒危的直接原因     

Development of microsatellite markers for the endangered Neotropical tree species Tibouchina papyrus (Melastomataceae)

We isolated and characterized 12 microsatellite loci for Tibouchina papyrus (Melastomataceae), an endangered species with narrow and disjunct range, endemics to a few localities in "cerrado rupestre" from Central Brazil. These microsatellites were obtained by sequencing of a genomic shotgun library for primer design. Leaves from 96 individuals collected in the three known local populations were genotyped using the 12 primers designed to analyze the polymorphisms at each locus. The number of alleles per locus ranged from one to six; two loci were monomorphic. Among the polymorphic loci, expected heterozygosities ranged from 0.161 to 0.714. Combined paternity exclusion probability was 0.957 and combined genetic identity (0.051) was high for studies on parentage. Tibouchina papyrus is a rare and endemic tree species of outcrop quartzite and sandstone soils, with highly isolated populations, which may have lead to the low degree of polymorphism that we detected. Also, motifs of most loci are larger than dinucleotide, which typically display lower levels of polymorphism.     

Assessment of the domestication state of ackee (Blighia sapida K.D. Koenig) in Benin based on AFLP and microsatellite markers

Ackee (Blighia sapida) is a native multipurpose species important for the livelihoods of the rural populations in Benin. Trees are found in natural forests or are managed by farmers in different traditional agroforestry systems. Genetic variation at amplified fragment length polymorphism (AFLP) markers, four nuclear microsatellites (nSSRs) and one chloroplast microsatellite (cpSSR) were investigated in 279 individuals from six wild and eight cultivated populations from Benin. The AFLP data revealed moderate levels of diversity of ackee in Benin (mean diversity values are proportion of polymorphic loci = 52.8% and Nei??s gene diversity = 0.157, for 375 AFLP fragments). The mean diversity values based on nSSR-markers are expected heterozygosity = 0.286, allelic richness = 2.77. Genetic variation of wild and cultivated populations did not differ markedly. AMOVA revealed that only 7.3 and 5.2% of the variation was partitioned among populations for nSSR- and AFLP-markers, respectively. A Mantel test based on these both marker-types revealed significant correlations between population pairwise geographic distance and genetic differentiation. Differentiation among cultivated populations was higher than among wild populations. The only polymorphic chloroplast microsatellite marker (ccmp7) showed three haplotypes. Cultivated populations from northeastern Benin were fixed on one haplotype which was not observed elsewhere indicating a different origin of these populations possibly from neighboring Nigeria. Farmer-led domestication had an impact on the spatial distribution of genetic variation but did not result in significant losses of diversity within populations. Measures to conserve genetic resources of ackee in each of the three main bioclimatic zones in Benin are proposed.     

Breakdown in the Process of Incipient Speciation in Anopheles gambiae

Understanding genetic causes and effects of speciation in sympatric populations of sexually reproducing eukaryotes is challenging, controversial, and of practical importance for controlling rapidly evolving pests and pathogens. The major African malaria vector mosquito Anopheles gambiae sensu stricto (s.s.) is considered to contain two incipient species with strong reproductive isolation, hybrids between the M and S molecular forms being very rare. Following recent observations of higher proportions of hybrid forms at a few sites in West Africa, we conducted new surveys of 12 sites in four contiguous countries (The Gambia, Senegal, Guinea-Bissau, and Republic of Guinea). Identification and genotyping of 3499 A. gambiae s.s. revealed high frequencies of M/S hybrid forms at each site, ranging from 5 to 42%, and a large spectrum of inbreeding coefficient values from 0.11 to 0.76, spanning most of the range expected between the alternative extremes of panmixia and assortative mating. Year-round sampling over 2 years at one of the sites in The Gambia showed that M/S hybrid forms had similar relative frequencies throughout periods of marked seasonal variation in mosquito breeding and abundance. Genome-wide scans with an Affymetrix high-density single-nucleotide polymorphism (SNP) microarray enabled replicate comparisons of pools of different molecular forms, in three separate populations. These showed strong differentiation between M and S forms only in the pericentromeric region of the X chromosome that contains the molecular form-specific marker locus, with only a few other loci showing minor differences. In the X chromosome, the M/S hybrid forms were more differentiated from M than from S forms, supporting a hypothesis of asymmetric introgression and backcrossing.     

Analysis of durum wheat germplasm adapted to different climatic conditions

A study of the extent and patterns of microsatellite diversity in 234 genotypes from Ethiopian durum wheat (Triticum turgidum) landraces was conducted to identify areas of diversity that could be used as a source of new germplasm for developing high yielding and stable varieties. Landraces belonging to nine populations, from three Ethiopian regions [Tigray (T), Gonder (G) and Shewa (S)] with different climates, were analysed by using 28 simple sequence repeat (SSR) markers. The level of polymorphism was high and quite consistent among populations underlining the great diversity existing. The highest level of diversity was found within populations, about 75.9%, while about 5.3% was attributed to differences between regions. The level of expected heterozygosity was on an average, rather high, ranging from 39% to 56%, whereas the observed heterozygosity was, on an average, limited to 14%. An average of about five alleles per locus was detected in each population. Nevertheless, alleles were not equally present in populations as confirmed by the high level of expected heterozygosity. The polymorphism information content (PIC) for the markers assessed showed a wide range of values from 0.14 to 0.92. The likelihood relationships among the nine Ethiopian populations indicated that the material collected in the Gonder region (a wet climate) was genetically more diverse than the materials from Shewa and Tigray (dryer climates). The high number of loci in linkage disequilibrium (LD), up to 23, has demonstrated that the loci were associated irrespective of their physical location. This holds true even if the loci are located on different chromosome arms. Genetic diversity values between populations was very different and was used to produce a dendrogram showing population relationships.     

Patterns of Gene Variation in Central and Marginal Populations of DROSOPHILA ROBUSTA

The central and marginal populations of D. robusta differ greatly in the level of inversion polymorphism; the marginal populations are monomorphic or nearly so and the central populations are highly polymorphic. This paper presents the frequencies of alleles at forty gene loci in various populations of D. robusta, studied by electrophoresis of proteins and enzymes. Population samples were obtained from eight widely separated populations of D. robusta which included the central, the extreme marginal and the intervening populations between the center and the margins. We find that the proportion of polymorphic loci and average heterozygosity per individual is slightly higher in the marginal populations than the central populations. In D. robusta on an average, 39% of the loci are polymorphic and the average proportion of loci heterozygous per individual is 11%. A breakdown of loci in three categories, viz, hydrolytic enzymes and some other enzymes, larval proteins and glycolytic and Kreb's cycle enzymes, shows that in all populations the level of polymorphism is highest in the hydrolytic enzymes, intermediate in larval proteins and least in the glycolytic and Kreb's cycle enzymes. On the average, the proportion of loci heterozygous per individual for three groups of loci is: hydrolytic enzymes and others (.164), larval proteins (.115) and glycolytic and Kreb's cycle enzymes (.037). We also observe that in all populations the level of polymorphism on the X chromosome is far less than the expected 38%; in salivary gland cells the euchromatic length of the X chromosome is 38% of the entire genome. Lower levels of polymorphism for the X chromosome loci are explained due to low probability of balanced polymorphisms for the X-linked loci since the conditions for establishment of balanced polymorphism for X-linked loci are more restrictive than for the autosomal loci.-The polymorphic loci can be grouped according to pattern of allele frequencies in different populations as follows: (1) The allele frequencies are similar in all populations at the XDH, Pep-1 and Hex-1 loci. (2) The alleles at the Est-1, Est-2, Amy loci and the AP-4(1.0) and the LAP-1(.90) alleles show north south clinal change in frequency. (3) There is north south and east west differentiation at the Pt-5, Pt-8 and Pt-9 loci and the allele AP-4(.81). (4) Polymorphism at loci such as Fum, B.Ox, Hex-8, Pep-2 and Pep-3 are restricted to only one or two of the populations. (5) Allele frequencies at the MDH and ODH loci fluctuate between populations. (6) Allele frequencies at many polymorphic loci such as Est-1, Est-2, LAP-1, AP-4, Pt-5, Pt-8, Pt-9, Pt-16, MDH, Fum change clinally within a gene arrangement. The pattern of gene variation in D. robusta is very complex and cannot be easily explained due to migration of neutral alleles between once-isolated populations or to semi-isolation of neutral alleles. The observations of the pattern of allele variation in different populations, high levels of polymorphism in the marginal populations which have small population size and low levels of polymorphism of the X chromosome loci all support the argument in favor of balancing selection as the main mechanism for the maintenance of these polymorphisms. Environmental factors must play a role in the maintenance of a great deal of these polymorphisms, since we observe clinal allele frequency changes even within a given inversion type.     

Polymerase chain reaction–restriction fragment length polymorphism markers for the fungal banana pathogen Mycosphaerella fijiensis

Polymerase chain reaction–restriction fragment length polymorphism markers were developed to study populations of the fungal banana pathogen Mycosphaerella fijiensis. Twelve markers were defined, 11 in anonymous and single‐copy nuclear DNA sequences and one in the internal transcribed spacer and 5.8S rDNA sequence. The polymerase chain reaction products obtained with locus‐specific primer pairs were digested with restriction enzymes to reveal polymorphism. Between five and 12 markers were polymorph in M. fijiensis populations from different geographical origins (Papua New Guinea, the Philippines, Cameroon and Latin America). The mean of allele number and gene diversity (expected heterozygosity) per locus in the different geographical populations ranged between 1.4 and 2.7 and 0.17 and 0.45, respectively.     

尼罗罗非鱼ghrelin基因的多态性及其与生长性状相关SNP位点的筛选

为了研究尼罗罗非鱼(Oreochromis niloticus)生长激素促分泌素基因(ghrelin)的多态性及其与生长的相关性, 研究以两个尼罗罗非鱼群体(快长群体和基础群体)的DNA样本各40份为模板, 通过PCR扩增和测序获得ghrelin基因序列。通过Dnasp v5和MEGA 5.0分析序列多态性、筛选有效SNP 位点; 采用Snapshot法对两个群体子代ghrelin基因中SNP位点进行基因分型, 然后分析SNP位点基因型与生长性状的相关性。结果表明, 快长群体ghrelin基因中的单核苷酸变异位点数(S)比基础群体要少, 而核苷酸多态性(Pi)和平均核苷酸差异数(K)要略高于基础群体。共筛得3个有效SNP 位点(S1、S2和S3), 均分布于第1个内含子中。遗传结构分析表明, 3个SNP 位点在两个群体的子代中均为低度多态性位点(PIC0.25), 但处于Hardy-Weinberg平衡(P0.05);快长群体子代中3个SNP 位点的观测杂合度、期望杂合度和多态信息含量等遗传多样性参数均小于基础群体子代的相应值, 3个SNP 位点的遗传多样性参数、基因型和基因频率在同一群体中高度一致, SNP 位点之间完全连锁。两个群体子代中3个SNP 位点处的优势基因型相同, 但快长群体子代中优势基因型频率要明显大于基础群体子代中相应基因型频率。对两个群体子代的生长性状与SNP基因型进行关联性分析的结果表明,尼罗罗非鱼个体的多项生长指标(体重、体长、体高、头长和尾柄高等)在不同基因型中存在显著差异(S1:GG AG, S2:TT AT, S3:AA AT)(P0.05)。D1双倍型(S1:GG, S2:TT, S3:AA)所对应的尼罗罗非鱼个体的多项生长指标(体重、体长、体高、头长和尾柄高等)显著高于D2双倍型(S1:AG, S2:AT, S3:AT)。以上结果表明, 尼罗罗非鱼ghrelin基因3个SNP 位点完全连锁, D1双倍型与快长性状密切相关, 可作为尼罗罗非鱼分子标记辅助育种的候选标记。