Importance Of Non-additive Genetic Effects Research Articles

Crossbreeding of three different shell color lines in the Pacific oyster reveals high heterosis for survival but low heterosis for growth

Heterosis is important for improving productive traits in aquaculture, but the heterosis between selected lines remains unclear in bivalve molluscs. Here, a diallel crosses among black shell (B, 7th generation), white shell (W, 7th generation) and orange shell (O, 6th generation) lines of the Pacific oyster were performed to examine the potential for exploiting heterosis of productive traits by crossbreeding of selected lines. Heterosis and combining abilities for growth and survival of 27 full-sib families were analyzed at both larval and juvenile stages, of which the juvenile stage was examined at two environments (Rongcheng and Rushan) for 10 months. The variance of specific combining ability accounts for the majority of the total variance for larval and juvenile survival and juvenile growth, which revealed the importance of non-additive genetic effects (heterosis) among these lines. Moreover, all reciprocal hybrids showed low or no heterosis for growth at both larval and juvenile stages, but a high heterosis for larval survival. This finding suggested that inter-line crossbreeding can be applied to improve the larval survival in hatcheries. Furthermore, four of six hybrid crosses showed positive HPH in Rushan but negative HPH in Rongcheng. The higher HPH at Rushan suggested that inter-line crossbreeding in C. gigas has more application value in Rushan. In addition, the survival of both black shell and white shell lines have been improved by crossing with the orange shell line. Especially, the hybrid cross WO (W♀ × O♂) can improve the survival rate of purebred WW by nearly 130% at larval stage and nearly 40% at juvenile stage. Overall, this study reveals the high heterosis for survival among selected lines in the Pacific oyster, and will be helpful for the utilization of non-additive genetic effects among existing selected lines in bivalves.

Estimation of Genetic Components and Heritability for Fruits Yield and Quality Characters in Tomato (Solanum Lycopersicom)

Six parental genotypes of tomato (Solanum Lycopersicom), i.e. Castel ruck (p1), Imperial (p2), Crystal (p3), Perso (p4), Pascal (p5) and Valcum valentime (p6) were crossed in a half diallel fashion to produce F1 in order to study some genetic components and ratios for some economic traits. The study consisted of twenty one genotypes; these genotypes were six inbred lines (parents) and fifteen F1 crosses. These twenty one genotypes were subjected to evaluation trial at Moshtohor village, Kalyobiya Governorate, Egypt during summer seasons of 2016 in a randomized complete block design with three replications. Data on yield and its components and fruit traits were recorded and subjected to statistical analysis to investigate Hayman's approach were used to study genetic components and heritability which control these traits. Data indicated that the additive component (D) was insignificant for average fruit weight, number of fruits and total yield per plant traits indicating the importance of non-additive effect in the inheritance of these traits. Meanwhile, the dominance genetic variations H1 and H2 were significant or highly significant for all studied fruits traits, showing the importance of dominance genetic effects in the inheritance of these traits. The average degree of dominance (H1/D) ½ showed over dominance for the average fruit weight, number of fruits and fruit yield per plant traits. The proportion of gene with positive and negative effects (H2/4H1) in the parents was lower than one quarter proportion, indicating unequal distribution between the positive and negative alleles among the parents. The ratio of dominant to recessive alleles (KD/KR) in the parents was more than (one), indicating that the six parents used in the present study carried more dominant than recessive allels. Heritability estimates in broad sense are very high for average fruit weight trait (100%), number of fruits (96%) and fruit yield per plant (92%), indicating the importance of genetic components of variation in the inheritance of these traits encouraging the usage of breeding programs to improve these traits. Meanwhile heritability estimates in narrow sense was low (2.7%, 1.4% and 0.7 %, respectively) clarifying the importance of non-additive genetic effects in the inheritance of these traits. These results indicate that a major of total phenotypic variances due to dominance and/or over-dominance and the environmental factor affects the inheritance of these traits. So it is of great importance to develop new hybrids in order to obtain maximum fruits number.

Combining ability of yield attributes traits, oil and protein contents in oil seed rape (Brassica napus) under normal and restricted nitrogen application

Combining ability of yield associated traits has been studied quite frequently in oilseed rape (Brassica napus L.) but it was hardly ever studied based on nitrogen levels variations. Six parents along with their 15 F2 half diallel crosses were evaluated in two nitrogen (N) levels including N0 and N+. Analysis of variance revealed significant mean squares of general and specific combining abilities (GCA and SCA) for all the traits studied. The high narrow-sense heritability estimates were found for seed yield and harvest index, implying the more importance of additive genetic effects for and consequently high selection efficiency for improving these traits. Due to low narrow-sense heritability estimates for oil and protein contents and therefore more importance of non-additive genetic effects, selection for improving these traits should be done in later segregating generations. The GCA × N level interaction was significant only for oil content which is indicating of more differences of GCA effect of this trait at two nitrogen levels. Significant N × SCA effect mean squares for harvest index and oil content, revealed significant variation of SCA effects of these traits in nitrogen levels application. Most of the crosses with high seed yield at N0 and N+ had at least one parent with positive GCA effect at both N levels. Among the six parents, PF7045/91 appeared to be the best combiner for seed yield at the N0. This variety also showed high GCA at the N+ but its low oil content at the N+ is certainly disadvantageous as the quality of the hybrid is often intermediate between the two parents.

Combining Ability Analysis of Some of Grain Yield Stress Indices in Rapeseed (Brassica Napus L.) Varieties

Although most of investigations showed that nitrogen fertilizers gave substantial rapeseed yield increases even in diverse and contradicting conditions but in a few studies were focused on genetic parameters of nitrogen stress effects. Combining ability of some of important grain yield stress indices based on application and non application of nitrogen (N+ and N0) was studied using half diallel of six spring rapeseed varieties and their 15 F2 progenies. Significant mean squares of general and specific combining abilities (GCA and SCA) were observed for potential yield(Yp), Stress yield(Ys), mean productivity (MP), geometric mean productivity (GMP), tolerance index (TOL), stress tolerance index (STI) and stress susceptibility index (SSI), indicating importance of additive and non-additive genetic effects for them. Non significant ratio of GCA to SCA mean square and low narrow-sense heritability estimates were detected for all the indices, indicating the prime importance of non-additive genetic effects. Significant positive GCA effect of Yp, Ys, MP, GMP and STI for PF7045/91 and significant negative GCA effects of them for Option500, indicated the same direction of GCA effects of these indices and GCA effects of Yp and Ys. On compare to SCA effects, most of crosses had significant high parent heterosis for Yp, Ys and and all the stress indices, therefore selection the better combinations based on heterosis will be more effective than SCA effect.

Analysis of Inbreeding Depression in Eight S1 Cassava Families

Inbreeding offers numerous advantages but also presents some problems for the genetic improvement of cassava (Manihot esculenta Crantz). One of the concerns is that inbreeding depression (ID) may be too drastic for (even partially) inbred materials to survive. A large experiment was conducted to quantify ID in cassava. S1 families from eight elite cultivars, each represented mostly by over 90 cloned genotypes, were produced and evaluated in a replicated trial at one location. The results from this evaluation allowed measurement of ID levels for key traits such as fresh root yield (63.9%), fresh foliage yield (37.9%), harvest index (26.5%), plant height (10.1%), and dry matter content in the roots (5.3%). Results also indicated (as expected) that ID, for a given trait, was not uniform among the eight families evaluated. For reasons provided in the article, the ID levels measured in this study may have been overestimated. Compared with the first experiences introducing inbreeding in temperate and tropical maize (Zea mays L.), we concluded that the use of homozygous progenitors in future cassava genetic enhancement is feasible. The average ID and frequency distributions within S1 families for different traits correlated well with the relative importance of nonadditive genetic effects controlling their inheritance as reported in the literature.

White Maize: Genetics of Quality and Agronomic Performance

White maize (Zea mays L.) is preferred for human consumption, but little is known about the genetic regulation of flour quality, and the potential value of genotypes adapted to temperate areas has not been reported. The objectives of this work were to assess the potential value of flint white maize inbreds from northwestern Spain and to determine the genetic effects of quality. A diallel among flint and dent white inbred lines was evaluated in northwestern Spain, and generation mean analyses were performed for three crosses representing flint by flint, dent by dent, and flint by dent combinations. Dent × dent hybrids had low density. Considering grain yield and density together, the best hybrids were EP64 × K301, EP71 × K301, and EC22 × Mo20W, which had poor milling test values, and high proportions of whole kernels. Considering the relative importance of nonadditive genetic effects, the final goal of breeding programs should be to obtain hybrids. Both additive and nonadditive genetic effects have to be taken into account to improve any of these traits in the flint genetic background. Moreover, it will be difficult to improve kernel density and proportion of whole kernels in any genetic background.

The use of animal models in the study of complex disease: all else is never equal or why do so many human studies fail to replicate animal findings?

The study of the genetics of complex human disease has met with limited success. Many findings with candidate genes fail to replicate despite seemingly overwhelming physiological data implicating the genes. In contrast, animal model studies of the same genes and disease models usually have more consistent results. We propose that one important reason for this is the ability to control genetic background in animal studies. The fact that controlling genetic background can produce more consistent results suggests that the failure to replicate human findings in the same diseases is due to variation in interacting genes. Hence, the contrasting nature of the findings from the different study designs indicates the importance of non-additive genetic effects on human disease. We discuss these issues and some methodological approaches that can detect multilocus effects, using hypertension as a model disease. This article contains supplementary material, which may be viewed at the BioEssays website at http://www.interscience.wiley.com/jpages/0265-9247/suppmat/index.html.

Heterosis and combining ability in a half diallel cross of kenaf ( Hibiscus cannabinus L.) in south Italy

The occurrence of heterosis has been evaluated in 45 F 1 combinations derived from ten parental genotypes of kenaf ( Hibiscus cannabinus L.) according to a diallelic scheme. In addition studies have been conducted to assess the combining ability for yield components, using method 2, model I, of the Griffing diallel analysis. The characteristics analyzed were: plant height, basal diameter, fresh and dry weight of bark and core of the useable stalk portion. Dry bark/dry woody core weight was evaluated also. The highly significant F-test values demonstrated the existence of variability for general combining ability (GCA) and specific combining ability (SCA), and for all the characters analysed. Mean squares of GCA were always (except for basal diameter) higher than those of SCA. However, when compared in terms of the average squared effects (components), the effects of SCA were greater than those of GCA, indicating the importance of non-additive genetic effects in determining the expression of yield components. Lines HC 625, HC 622 and HC 602 were the best general combiners for the most important characters. Heterosis for dry bark weight was highest in HC 602×HC 726.

Components of Genetic Variance in Milk Yield

The purpose of this research was to determine the importance of non-additive genetic effects and genetic maternal effects in the inheritance of milk production in dairy cattle. Expressing milk yield as a deviation from herdmate average eliminated most of the variation due to herds, years, seasons, and their interactions without affecting the expression of additive genetic differences between sires for milk yield. It is clearly demonstrated that expressing records as deviations does not eliminate effects of dam and herd-year-season confounding. Genetic maternal effects were found to be of little or no importance. The magnitude of the sire by maternal grandsire component estimate implies that non-additive genetic variance is near zero. An example is used to show that even should genetic maternal effects and non-additive genetic effects be sizeable, the selection index weights for records on relatives and the accuracy of the index are only slightly different from those obtained assuming strictly additive inheritance.