Overdominance Effects Research Articles

The formation of nicotine heterosis is mainly achieved by enhancing the nicotine transport capacity in hybrids

Nicotine exhibits obvious heterosis, which can be used to create Nicotiana tabacum L. (tobacco) varieties with varying nicotine content. However, the reasons for the formation of nicotine heterosis and its relationship to nicotine transport and accumulation remain unknown. This study conducted a comprehensive analysis of six tobacco hybrids with varying heterosis levels and their parent materials from various aspects, such as phenotype, physiology, and transcriptomics. The results showed that the direct path coefficient of transport heterosis to nicotine heterosis was highest in hybrids, at 0.98, and a highly significant positive correlation between the two. The plant height, thick stalk circumference, large flow of tissue fluid in the stalk, and high nicotine concentration of tobacco were the underlying factors that led to the strong nicotine transport capacity of hybrids. The formation of nicotine transport heterosis in hybrids was mainly influenced by non-additive gene effects (accounting for 89.93%), with over-dominant effects playing a dominant role (accounting for 58.79%). Among non-additive expression DEGs, nicotine transporter related multi antimicrobial extrusion protein, drug/metabolite transporter, ABC family transporter, and glutathione S-transferase were significantly upregulated in hybrid strains. The RT-qPCR results indicated that these genes related nicotine transport also exhibited heterosis at the expression level. Our results revealed that the formation of nicotine heterosis is mainly achieved by enhancing the nicotine transport capacity in hybrids. The results are not only beneficial for promoting the theoretical study of nicotine heterosis in tobacco and the breeding and utilization of hybrids, but are also of great significance for guiding nicotine production and promoting its multipurpose utilization.

The Dominance of Coinfecting Parasites' Indirect Genetic Effects on Host Traits.

AbstractIndirect genetic effects (IGEs) exist when there is heritable variation in one organism's ability to alter a second organism's traits. For example, parasites have antigens that can induce a host immune response, as well as disparate strategies to evade or suppress host immunity; among-parasite genetic variation in these antigens generates among-host variation in immune traits. Here, we experimentally show that the cestode parasite Schistocephalus solidus exerts an IGE on an immune trait (peritoneal fibrosis) in its threespine stickleback host: stickleback developed strong fibrosis after exposure to some parasite genotypes but not others. A complication arises during coinfection, when two or more parasite genotypes may impose conflicting IGEs on the same host trait. What parasite-controlled trait will the host express? Will the host trait reflect the more immune-stimulatory parasite genotype or the more immune-evasive genotype? These alternatives can be quantified by estimating the dominance coefficient, as if a coinfected host were a heterozygote. We experimentally estimated the dominance of S. solidus IGEs by coinjecting antigens from different parasite genotypes. Contrary to our a priori hypotheses, coinjected antigens induced an overdominant effect, stronger than either parasite's antigens alone. We present a mathematical model showing that the value of this IGE dominance is biologically important, affecting the evolutionary dynamics of parasites in a density- and frequency-dependent manner. The model indicates that overdominance would be detrimental to immigrants when resident prevalence is high. This combination of experimental data and modeling provides an example of a parasite IGE on host traits and the evolutionary significance of IGE dominance.

Genetic Component Analysis in Fruit Yield and Quality Traits in Okra [Abelmoschus esculentus (L.) Moench

A half-diallel cross involving nine okra genotypes was utilized to investigate the inheritance of fruit yield and its component traits. Data from the F1 generation and the parent genotypes were analysed using Hayman's (1954) diallel method. The additive genetic component (D) was found to be significant for the traits like days to last picking in environment E1, and for the number of fruits per plant in environments E2 and E3, but non-significant across all environments for fruit yield per plant. The dominant components (H1 and H2) were found significant for all traits studied under all environmental condition. This revealed that both additive and non-additive gene actions play a vital role in the expression of the traits studied. The dominant component's (H1 and H2) relative magnitude was greater than the additive component for most of the traits, suggesting the importance of dominance effects on expression of those traits. The average degree of dominance showed an overdominance effect for the traits studied. The ratio of dominant to recessive genes indicated that the parents had an excess of dominant genes for fruit yield per plant. Thus stated the presence of overdominance for yield, reciprocal technique is the most effective recurrent breeding scheme for producing improved hybrids.

Breed of origin analysis in genome-wide association studies: enhancing SNP-based insights into production traits in a commercial Brangus population

BackgroundCarcass weight (HCW) and marbling (MARB) are critical for meat quality and market value in beef cattle. In composite breeds like Brangus, which meld the genetics of Angus and Brahman, SNP-based analyses have illuminated some genetic influences on these traits, but they fall short in fully capturing the nuanced effects of breed of origin alleles (BOA) on these traits. Focus on the impacts of BOA on phenotypic features within Brangus populations can result in a more profound understanding of the specific influences of Angus and Brahman genetics. Moreover, the consideration of BOA becomes particularly significant when evaluating dominance effects contributing to heterosis in crossbred populations. BOA provides a more comprehensive measure of heterosis due to its ability to differentiate the distinct genetic contributions originating from each parent breed. This detailed understanding of genetic effects is essential for making informed breeding decisions to optimize the benefits of heterosis in composite breeds like Brangus.ObjectiveThis study aims to identify quantitative trait loci (QTL) influencing HCW and MARB by utilizing SNP and BOA information, incorporating additive, dominance, and overdominance effects within a multi-generational Brangus commercial herd.MethodsWe analyzed phenotypic data from 1,066 genotyped Brangus steers. BOA inference was performed using LAMP-LD software using Angus and Brahman reference sets. SNP-based and BOA-based GWAS were then conducted considering additive, dominance, and overdominance models.ResultsThe study identified numerous QTLs for HCW and MARB. A notable QTL for HCW was associated to the SGCB gene, pivotal for muscle growth, and was identified solely in the BOA GWAS. Several BOA GWAS QTLs exhibited a dominance effect underscoring their importance in estimating heterosis.ConclusionsOur findings demonstrate that SNP-based methods may not detect all genetic variation affecting economically important traits in composite breeds. BOA inclusion in genomic evaluations is crucial for identifying genetic regions contributing to trait variation and for understanding the dominance value underpinning heterosis. By considering BOA, we gain a deeper understanding of genetic interactions and heterosis, which is integral to advancing breeding programs. The incorporation of BOA is recommended for comprehensive genomic evaluations to optimize trait improvements in crossbred cattle populations.

Effect of the “Naked neck” gene (Na) on the growth of indigenous chicken fed with suboptimal feed rations in Cameroon

The effect of the naked neck gene (Na) was assessed on growth parameters of the native chicken fed with two suboptimal rations (R1 and R2), and one optimal ration (R3) from 6 to 16 weeks of age. A total of 270 hens of 3 genetic types (homozygous (NaNa) naked neck, heterozygous (Nana) and normal type (nana) chicken) for three different feed rations including two sub-optimal rations (R1, R2) and one optimal ration (R3). Hence, 30 pullets per experimental unit for each genetic type receiving the same ration were used. The animals were subjected to the same experimental conditions except for the tested factor. The starter ration was served during the first six weeks then relayed by the experimental rations. A two-way ANOVA was used to test the main effects and interactions whereas the animal model was used for the estimates of the genotype and feed ration on the growth and related traits. Irrespective of the genotype, the highest growth parameter (p<0.05) was obtained with R3 with the lowest feed efficiency from 12 to 16 weeks. The mortality rate (MR) ranged from 3 to 9% cumulated at 6 and 8 weeks of age. The overdominance effect was confirmed for both the bodyweight (BW) and MR. The Na gene improved the weight gain from +1 to + 14 g from 10 to 16 weeks with optimal feed conditions against -6.67 to +4.33g with suboptimal feed. The more beneficial effect on FCR has been observed in homozygote NaNa with +1.07 to +1.27g and -0.43 to -1.63g for R3 and R1 respectively. This study confirms the importance of the Na gene as a good candidate to improve the growth rate and feed efficiency of native chickens. It also provides an effective protocol for the evaluation of major gene candidates for selection in low input production systems.

The “Naked neck” gene and the adaptability of the native chicken to heat stress on station in Cameroon

The rational use of the native chicken genetic resource is seen a viable option for sustainably improving poultry meat production in Cameroon. This study aimed at assessing the potential of the Na gene for resilience under acute heat stress. The study was done in two trials. Firstly, a total of 180 young roosters reared in similar management conditions from the 1st to the 8th week of age were randomly distributed per genotype according to a 3 x 2 factorial design including two treatments (acute and moderate ambient temperatures) of 90 birds each and three genotypes (Na*Na, na*na and Na*na) of 30 birds per treatment. Treatments consisted of moderate and acute ambient temperatures of 25-27°C and 39 - 42°C respectively for 5 hours/day from 8 to 12 weeks of age. The genotypes within and between the treatments were compared for body weight (BW), average daily weight gain (ADG), water consumption (WC), feed consumption (FC), and feed conversion ratio (FCR). Results showed that the na*na and Na*na were statistically comparable but superior to the Na*Na genotype under moderate temperature. The three genotypes were significantly affected (P<0.05) by the heat stress. However, the Na*na was less affected and maintained the highest ADG and lowest FCR. For the second trial, 90 birds including 30 birds randomly sampled per genotype were compared for the feathering intensity and five carcass characteristics and giblets at 24-week-old. The results revealed an association of the “Na” gene with 21 to 50 % feather reduction in heterozygote and homozygote respectively whereas heterozygote naked neck had greater body and carcass weight as well as giblet and head weights (P<0.05). The animal model equation could clearly quantify the genotype effect. The phenotypic advantage evidenced for the Na gene is confirmed as an adaptation to heat stress whereas the significant superiority of heterozygote Na*na for most of the traits opens a window for the valorisation of potential overdominance effects for poultry breeding in hot climates.

Structure and function of rice hybrid genomes reveal genetic basis and optimal performance of heterosis

Exploitation of crop heterosis is crucial for increasing global agriculture production. However, the quantitative genomic analysis of heterosis was lacking, and there is currently no effective prediction tool to optimize cross-combinations. Here 2,839 rice hybrid cultivars and 9,839 segregation individuals were resequenced and phenotyped. Our findings demonstrated that indica–indica hybrid-improving breeding was a process that broadened genetic resources, pyramided breeding-favorable alleles through combinatorial selection and collaboratively improved both parents by eliminating the inferior alleles at negative dominant loci. Furthermore, we revealed that widespread genetic complementarity contributed to indica–japonica intersubspecific heterosis in yield traits, with dominance effect loci making a greater contribution to phenotypic variance than overdominance effect loci. On the basis of the comprehensive dataset, a genomic model applicable to diverse rice varieties was developed and optimized to predict the performance of hybrid combinations. Our data offer a valuable resource for advancing the understanding and facilitating the utilization of heterosis in rice.

Genome-Wide Association Study of Age at First Calving in U.S. Holstein Cows.

A genome-wide association study (GWAS) of age at first calving (AFC) using 813,114 first lactation Holstein cows and 75,524 SNPs identified 2063 additive effects and 29 dominance effects with p-values < 10-8. Three chromosomes had highly significant additive effects in the regions of 7.86-8.12 Mb of Chr15, 27.07-27.48 Mb and 31.25-32.11 Mb of Chr19, and 26.92-32.60 Mb of Chr23. Two of the genes in those regions were reproductive hormone genes with known biological functions that should be relevant to AFC, the sex hormone binding globulin (SHBG) gene, and the progesterone receptor (PGR) gene. The most significant dominance effects were near or in EIF4B and AAAS of Chr05 and AFF1 and KLHL8 of Chr06. All dominance effects were positive overdominance effects where the heterozygous genotype had an advantage, and the homozygous recessive genotype of each SNP had a very negative dominance value. Results from this study provided new evidence and understanding about the genetic variants and genome regions affecting AFC in U.S. Holstein cows.

Screening of Grain Development Heterosis Candidate Genes by Integrating QTL Mapping and RNA-Seq in Super Hybrid Rice WFYT025

The application of heterosis during plant breeding increases rice grain yield. However, there have been limited studies on heterosis during rice grain development during the grain-filling stage; therefore, the genetic basis of heterosis for grain development during the grain-filling stage should be highly valued. In this study, a hybrid combination with the super hybrid rice WFYT025 was used to perform a transcriptomic dynamic analysis in grains at the beginning and middle grain-filling stages. A total of 1556 and 1507 transcripts that were differentially expressed between WFYT025 and its parents (DGHP) were identified at 1-day post-anthesis (DPA) and at 10 DPA, respectively. The analysis of the genetic effects of heterosis showed that the over-dominant effect (66.90% and 55.87%) was the main mode of action during grain development. The KEGG pathway and GO analysis of the DGHP indicated that the gibberellin biosynthetic, starch metabolic, and diterpenoid biosynthetic signaling pathways may be associated with heterosis during grain development. To further explore the candidate genes for grain development heterosis, a recombinant inbred line (RILs) population with a high-density genetic map of 2578 bin markers was constructed by crossing the parents of WFYT025, and nine stable QTLs for grain weight-related traits were identified. By comparing the DGHP with 20 QTLs, LOC_Os02g28820, LOC_Os02g32580, LOC_Os04g25440, and LOC_Os12g04980 were identified as grain development heterosis-related candidate genes. These findings provide resources for the study of heterosis during the grain development of super hybrid rice and provide valuable theoretical references for the cloning and functional analysis of heterosis-related genes.

Examining the Inheritance of Watermelon Fruit Traits by Hayman's Graphical Approach.

Watermelon traits such as yield and other agronomic traits are highly environmentally sensitive and regulated by multiple genes; therefore, by understanding the genetic structure, the heritability and genetic influence of different traits can improve them. Five watermelon lines were crossed in a 5 × 5 full diallel parental design to estimate the genetic effect and heritability of fruit traits. Treatments were evaluated on the farm using a random complete block design. Analysis of the results showed a significant difference between genotypes, which was observed for all the studied traits at the probability level of 1%. Hayman's graphical method showed that the contribution of the nonadditive effects was more important than that of the additive effect to control most of the traits. Fruit maturation and pericarp thickness traits were regulated by incomplete dominance gene effects, and other traits were regulated by overdominance effects. The trait heritability varied between at least 0.013 and 0.352 for the fruit weight and fruit number, respectively. Results demonstrated that some traits can be modified based on the heterozygosity and production of hybrid variety methods, while the hybrid and selection in an advanced generation method can be suggested in watermelon breeding programs to breed other traits.

Genetic dissection of ear-related traits using immortalized F2 population in maize

Ear-related traits are often selection targets for maize improvement. This study used an immortalized F2 (IF2) population to elucidate the genetic basis of ear-related traits. Twelve ear-related traits (namely, row number (RN), kernel number per row (KNPR), ear length (EL), ear diameter (ED), ten-kernel thickness (TKT), ear weight (EW), cob diameter (CD), kernel length (KL), kernel width (KW), grain weight per ear (GW), 100-kernel weight (HKW), and grain yield per plot (GY)), were collected from the IF2 population. The ear-related traits were comprised of 265 crosses derived from 516 individuals of the recombinant inbred lines (RILs) under two separated environments in 2017 and 2018, respectively. Quantitative trait loci (QTLs) analyses identified 165 ear traits related QTLs, which explained phenotypic variation ranging from 0.1 to 12.66%. Among the 165 QTLs, 19 underlying nine ear-related traits (CD, ED, GY, RN, TKT, HKW, KL, GW, and KNPR) were identified across multiple environments and recognized as reliable QTLs. Furthermore, 44.85% of the total QTLs showed an overdominance effect, and 12.72% showed a dominance effect. Additionally, we found 35 genomic regions exhibiting pleiotropic effects across the whole maize genome, and 17 heterotic loci (HLs) for RN, EL, ED and EW were identified. The results provide insights into genetic components of ear-related traits and enhance the understanding of the genetic basis of heterosis in maize.

Identification of Heterotic Loci with Desirable Allelic Interaction to Increase Yield in Rice

Heterosis denotes the superiority of a hybrid plant over its parents. The use of heterosis has contributed significantly to yield improvement in crops. However, the genetic and molecular bases on heterosis are not fully understood. A large number of heterotic loci were identified for 12 yield-related traits in one parental population of chromosome segment substitution lines (CSSLs) and two test populations, which were interconnected by CSSLs derived from two rice genome-sequenced cultivars, Nipponbare and Zhenshan 97. Seventy-five heterotic loci were identified in both homozygous background of Zhenshan 97 and heterogeneous background of an elite hybrid cultivar Shanyou 63. Among the detected loci, at least 11 were colocalized in the same regions encompassing previously reported heterosis-associated genes. Furthermore, a heterotic locus Ghd8NIP for yield advantage was verified using transgenic experiments. Various allelic interaction at Ghd8 exhibited different heterosis levels in hetero-allelic combinations of five near-isogenic lines that contain a particular allele. The significant overdominance effects from some hetero-allelic combinations were found to improve yield heterosis in hybrid cultivars. Our findings support the role of allelic interaction at heterotic loci in the improvement of yield potential, which will be helpful for dissecting the genetic basis of heterosis and provide an optional strategy for the allele replacement in molecular breeding programs in hybrid rice.

The relationship between positive parenting and adolescent prosocial behaviour: The mediating role of empathy and the moderating role of the oxytocin receptor gene

<p id=p00005>Prosocial behaviour, that is, behaviour intended to benefit others, has been linked to a variety of desirable traits, including positive relationships, better academic performance and lower levels of antisocial behaviours. As such, the origins and the mechanisms underlying the remarkable individual differences in prosocial behaviour are the focus of an increasing number of studies, with numerous research consistently documenting the important role of positive parenting and empathy. Notably, differentiating between cognitive and emotional components of empathy may help further clarify the processes by which parenting eventuates in prosocial behaviour. Although all children may be impacted by parenting, some children benefit more than others from good-quality rearing. Recent research has suggested that the oxytocin receptor (<italic>OXTR</italic>) gene rs53576 polymorphism could determine the degree to which a child is influenced by environment. The biological function of rs53576 polymorphism has yet to be delineated, and the literature is mixed with regard to heterozygote (AG) grouping; thus, the implications for AG grouping are not well understood. Therefore, the dummy coding, additive coding, dominant coding and recessive coding models were all investigated in this study to test the nature of gene effect. This study aimed to extend previous studies on the association between parenting and prosocial behaviour by examining the mediating role of cognitive and emotional empathy and the moderating role of the <italic>OXTR</italic> gene. <p id=p00010>The participants were 1082 mother-offspring dyads (adolescents’ mean age: 12.32 ± 0.48 years, 50.3% females) recruited from the community. At Time 1, mothers reported their positive parenting via the Chinese version of the Child-Rearing Practices Report (CRPR) and peer-rated adolescents’ prosocial behaviours. At Time 2, adolescent-reported perspective-taking and empathic concern, peer-rated prosocial behaviours and saliva samples were collected. All measures showed good reliability. Genotyping at <italic>OXTR</italic> gene was performed with MassARRAY RT software version 3.0.0.4 and analysed using the MassARRAY Typer software version 3.4 (Sequenom). <p id=p00015>Results showed that adolescents who received higher levels of maternal positive parenting exhibited more prosocial behaviours. However, the direct effect of positive parenting on prosocial behaviour became nonsignificant after controlling for baseline prosocial behaviour. Cognitive empathy, but not emotional empathy, mediated the association between positive parenting and prosocial behaviour. Specifically, positive parenting was positively associated with cognitive empathy, which in turn was positively associated with adolescent prosocial behaviour. Further, this mediation was moderated by the <italic>OXTR</italic> gene rs53576 polymorphism. For adolescents with AA and GG genotypes, positive parenting was related to higher levels of cognitive empathy, which increased prosocial behaviour. However, this mediation effect was not observed among adolescents with AG genotype. In addition, the results revealed evidence for an overdominance model for <italic>OXTR</italic> rs53576. Moreover, the G × E term predicted cognitive empathy but not prosocial behaviour. This finding suggests that cognitive empathy may be an endophenotype closer along the causal chain to the genotype and that the strength of the G × E effects was greater for empathy than for distal behavioural outcomes. <p id=p00020>These findings add to our understanding of how empathy and genetic factors contribute to adolescents’ prosocial behaviour within the family context. In addition, these results suggest that cognitive and emotional aspects of empathy are likely to be involved—in somewhat different psychosocial mechanisms—in the development of prosocial behaviour. Notably, the overdominance effect of <italic>OXTR</italic> should be interpreted with caution until replicated. However, when a three-category polymorphic genotype is used, as is commonly applied when modelling a dominant or recessive effect, both false positive and false negative results can occur, and the nature of the interaction can be misrepresented.

НАСЛЕДОВАНИЕ И ГЕНЕТИЧЕСКИЙ КОНТРОЛЬ МАССЫ ЗЕРНА С КОЛОСА У ЯЧМЕНЯ

The aim of the study was to investigate the systems of genetic control of the trait “grain weight per main spike” in spring barley in the system of diallel crosses to optimize the breeding process for yield. Six varieties of barley were used as parental forms: Condor and Omskiy naked 1 (hulless), Margret, Lun, Nutans 553, and Anna (hulled). Crosses according to the full diallelic scheme were performed in 2008 and 2009. Field experiments were carried out in the forest-steppe of Penza region in 2009 and 2010 with contrasting hydrothermal regimes. In most hybrid populations, the grain weight per spike was inherited according to the type of overdominance and complete dominance of the parent with a high value of the trait. The analysis of the combining ability by B.Griffing showed that both additive and non-additive effects were present in the control of the trait; their balance varied by years and genotypes. The correlation coefficients between the general combining ability (GCA) and the degree of the trait in parental varieties (r=0.76...0.96) indicate that the selection of pairs for crosses can be carried out on the basis of high values of grain weight per spike, especially in a dry year. Genetic analysis by B.Hayman showed the prevalence of the effects of overdominance in the control of the trait; in 2009, complementary epistasis was also registered. Overdominance and non-additive effects in the control of a trait complicates selection in early generations, which is confirmed by the differences between the values of heritability coefficients in the broad sense (H2=0.79...0.94) and in the narrow sense (h2=0.24...0.59). The largest number of dominant genes controlling the grain weight per spike was found in Margret in both years of research and Anna in the dry year. These varieties are also distinguished for the consistently positive effects of GCA and are recommended as donors of the trait for breeding

Genetic dissection of heterosis of indica\u2013japonica by introgression line, recombinant inbred line and their testcross populations

The successful implementation of heterosis in rice has significantly enhanced rice productivity, but the genetic basis of heterosis in rice remains unclear. To understand the genetic basis of heterosis in rice, main-effect and epistatic quantitative trait loci (QTLs) associated with heterosis for grain yield-related traits in the four related rice mapping populations derived from Xiushui09 (XS09) (japonica) and IR2061 (indica), were dissected using single nucleotide polymorphism bin maps and replicated phenotyping experiments under two locations. Most mid-parent heterosis of testcross F1s (TCF1s) of XS09 background introgression lines (XSILs) with Peiai64S were significantly higher than those of TCF1s of recombinant inbred lines (RILs) with PA64S at two locations, suggesting that the effects of heterosis was influenced by the proportion of introgression of IR2061’s genome into XS09 background. A total of 81 main-effect QTLs (M-QTLs) and 41 epistatic QTLs were identified for the phenotypic variations of four traits of RILs and XSILs, TCF1s and absolute mid-parent heterosis in two locations. Furthermore, overdominance and underdominance were detected to play predominant effects on most traits in this study, suggesting overdominance and underdominance as well as epistasis are the main genetic bases of heterosis in rice. Some M-QTLs exhibiting positive overdominance effects such as qPN1.2, qPN1.5 and qPN4.3 for increased panicle number per plant, qGYP9 and qGYP12.1 for increased grain yield per plant, and qTGW3.4 and qTGW8.2 for enhanced 1000-grain weight would be highly valuable for breeding to enhance grain yield of hybrid rice by marker-assisted selection.

Associative Overdominance and Negative Epistasis Shape Genome-Wide Ancestry Landscape in Supplemented Fish Populations.

The interplay between recombination rate, genetic drift and selection modulates variation in genome-wide ancestry. Understanding the selective processes at play is of prime importance toward predicting potential beneficial or negative effects of supplementation with domestic strains (i.e., human-introduced strains). In a system of lacustrine populations supplemented with a single domestic strain, we documented how population genetic diversity and stocking intensity produced lake-specific patterns of domestic ancestry by taking the species’ local recombination rate into consideration. We used 552 Brook Charr (Salvelinus fontinalis) from 22 small lacustrine populations, genotyped at ~32,400 mapped SNPs. We observed highly variable patterns of domestic ancestry between each of the 22 populations without any consistency in introgression patterns of the domestic ancestry. Our results suggest that such lake-specific ancestry patterns were mainly due to variable associative overdominance (AOD) effects among populations (i.e., potential positive effects due to the masking of possible deleterious alleles in low recombining regions). Signatures of AOD effects were also emphasized by highly variable patterns of genetic diversity among and within lakes, potentially driven by predominant genetic drift in those small isolated populations. Local negative effects such as negative epistasis (i.e., potential genetic incompatibilities between the native and the introduced population) potentially reflecting precursory signs of outbreeding depression were also observed at a chromosomal scale. Consequently, in order to improve conservation practices and management strategies, it became necessary to assess the consequences of supplementation at the population level by taking into account both genetic diversity and stocking intensity when available.

A potential role for overdominance in the maintenance of colour variation in the Neotropical tortoise beetle, Chelymorpha alternans.

The presence of persistent polymorphisms within natural populations elicits the question of how such polymorphisms are maintained. All else equal, genetic drift and natural selection should remove genetic variants from populations. Disassortative mating and overdominance are potential mechanisms for maintaining variation within populations. Here, we consider the potential role of these mechanisms in maintaining variation in colour pattern in the tortoise beetle, Chelymorpha alternans. Five colour morphs distinguished by elytral and pronotal coloration are largely determined by a single locus of large effect with four segregating alleles. As many as four morphs co-occur in natural populations. We first assessed whether disassortative mating might maintain this polymorphism. To test for assortative and disassortative mating, we paired females with two males, one with the same colour pattern as the female and one with a different colour pattern and examined the colour patterns of the offspring. We found strong evidence for random mating as a function of colour pattern. We next assessed whether differences in offspring survival among assortative and disassortative male-female pairs maintain colour variation. Crosses involving disassortative pairings had significantly higher offspring survival during development and resulted in more adult progeny. This result is consistent with the effects of overdominance, whereby outcrossed individuals have higher fitness than their homozygous counterparts. Overall, differences in offspring survival appear to play a greater role in maintaining polymorphisms than nonrandom mating in species.

Association study of single nucleotide polymorphism in tryptophan hydroxylase 1 gene with adolescent idiopathic scoliosis: A meta-analysis.

Adolescent idiopathic scoliosis is a common spinal deformity among children and adolescents worldwide with its etiology uncertain. Over a decade, a single nucleotide polymorphism rs10488682 in tryptophan hydroxylase 1 (TPH1) gene has been investigated in several association studies. We perform this study to summarize the current evidence of TPH1 rs10488682 polymorphisms and adolescent idiopathic scoliosis (AIS). Six databases were systematically searched: PubMed, Embase, Cochrane Library, Web of Science, Chinese Biomedical Literature, and Wanfang database. Eligible case-control studies related to TPH1 and AIS were selected. Reference lists of them were reviewed for more available studies. Two authors independently screened and evaluated the literature and extracted data. The odds ratios and 95% confidence intervals were derived in association tests. Subgroup analysis was conducted by ethnicity. Sensitivity analysis was performed to examine the stability of the overall results. A total of 1006 cases and 1557 controls in 3 independent studies were included for meta-analysis. Statistical significance was discovered in heterozygote model (AT vs AA: OR = 1.741, 95%Cl = 1.100-2.753, P = .018 < .05, I2 = 0%), recessive model (AA vs AT + TT: OR = 0.640, 95%Cl = 0.414-0.990, P = .045 < .05, I2 = 0%) and over-dominant model (AT vs AA + TT: OR = 1.366, 95%Cl = 1.115-1.673, P = .003 < .05, I2 = 84.7%) in overall populations. Similar associations were also found in the Caucasian population. No significant associations were found in other genotypic comparisons and allelic comparisons. Statistically significant correlations were discovered between the TPH1 rs10488682 polymorphisms and AIS. Heterozygous AT genotype seems to be risky with an over-dominant effect. Ethnicity appears to modify the disease association. Not applicable.

Mapping Solanum chacoense mediated Colorado potato beetle (Leptinotarsa decemlineata) resistance in a self-compatible F2 diploid population.

A major QTL on chromosome 2 associated with leptine biosynthesis and Colorado potato beetle resistance was identified in a diploid S. chacoense F2 population using linkage mapping and bulk-segregant analysis. We examined the genetic features underlying leptine glycoalkaloid mediated Colorado potato beetle (Leptinotarsa decemlineata) host plant resistance in a diploid F2 mapping population of 233 individuals derived from Solanum chacoense lines USDA8380-1 and M6. The presence of foliar leptine glycoalkaloids in this population segregated as a single dominant gene and displayed continuous distribution of accumulated quantity in those individuals producing the compound. Using biparental linkage mapping, a major overlapping QTL region with partial dominance effects was identified on chromosome 2 explaining 49.3% and 34.1% of the variance in Colorado potato beetle field resistance and leptine accumulation, respectively. Association of this putative resistance region on chromosome 2 was further studied in an expanded F2 population in a subsequent field season. Loci significantly associated with leptine synthesis colocalized to chromosome 2. Significant correlation between increased leptine content and decreased Colorado potato beetle defoliation suggests a single QTL on chromosome 2. Additionally, a minor QTL with overdominance effects explaining 6.2% associated with Colorado potato beetle resistance donated by susceptible parent M6 was identified on chromosome 7. Bulk segregant whole genome sequencing of the same F2 population detected QTL associated with Colorado potato beetle resistance on chromosomes 2, 4, 6, 7, and 12. Weighted gene co-expression network analysis of parental lines and resistant and susceptible F2 individuals identified a tetratricopeptide repeat containing protein with a putative regulatory function and a previously uncharacterized acetyltransferase within the QTL region on chromosome 2, possiblyunder the control of a regulatory Tap46 subunit within the minor QTL on chromosome 12.

Heterotic Potential, Potence Ratio, Combining Ability and Genetic Control of Quality and Yield Traits in Bell Pepper Under Net-House Conditions of NW Himalayas

The present experiment was carried out with the aim of identifying outstanding specific combiners and best parental lines along with the understanding of genetic control of fruit quality and yield traits of bell pepper under net-house conditions in northwestern Himalayas of India. Eight inbred lines were crossed in half diallel manner, and the resulted twenty-eight F1 hybrids along with a standard check variety were evaluated under net-house conditions. California Wonder and Solan Bharpur parental lines were found to be the best combiner for earliness, whereas Yolo Wonder, California Wonder, Nishath-1 and UHFBP-3 reported as best parental line for fruit quality, yield and yield contributing traits based on their general combining effects. Solan Bharpur × Yolo Wonder, Yolo Wonder × Nishath-1, California Wonder × Solan Bharpur, California Wonder × UHFBP-3 and UHFBP-3 × KC-12 cross-combinations found outstanding based on heterosis and specific combining ability for most of the traits under net-house condition. The present studied hybrids illustrated the presence of over-dominance effect for yield and yield contributing traits under study. Predominance of nonadditive gene action for all the characters suggested the usefulness of exploitation of hybrid vigor.