Changes of genetic variances and heritability by effect of selection in a Mexican local variety of Squash

A local variety of squash (Cucurbita pepo L.), ‘Round Zuchinni’ type from Los Reyes Acatlixhuayan State of México, México, was simultaneously evaluated and selected. The objective was to study effect of selection on genetic variance and heritability. Additive genetic variance decreased in seven of nine traits studied: fruit height (79.93 %); fruit weight (65.72 %); fruit width (60.91 %); flesh thickness (57.66 %); flesh color (43.70 %); dry weight of seed (39.54 %); flesh flavor (16.60 %); except in width and seed length traits where it increased 63.40 % and 0.81 %, respectively. Only weight of seed had dominance genetic variance. The coefficient of additive genetic variance (CVA) fluctuated from 9.4 to 61.7 % in the first cycle, and from 9.4 to 51.8 % in the second cycle of selection-evaluation among traits. Heritability diminished in seven from nine characters. In general, the estimated genetic variances (additive and dominance) and heritability decreased as a result of combined selection of falf sib families.

The genetic architecture of teosinte catalyzed and constrained maize domestication

The process of evolution under domestication has been studied using phylogenetics, population genetics–genomics, quantitative trait locus (QTL) mapping, gene expression assays, and archaeology. Here, we apply an evolutionary quantitative genetic approach to understand the constraints imposed by the genetic architecture of trait variation in teosinte, the wild ancestor of maize, and the consequences of domestication on genetic architecture. Using modern teosinte and maize landrace populations as proxies for the ancestor and domesticate, respectively, we estimated heritabilities, additive and dominance genetic variances, genetic-by-environment variances, genetic correlations, and genetic covariances for 18 domestication-related traits using realized genomic relationships estimated from genome-wide markers. We found a reduction in heritabilities across most traits, and the reduction is stronger in reproductive traits (size and numbers of grains and ears) than vegetative traits. We observed larger depletion in additive genetic variance than dominance genetic variance. Selection intensities during domestication were weak for all traits, with reproductive traits showing the highest values. For 17 of 18 traits, neutral divergence is rejected, suggesting they were targets of selection during domestication. Yield (total grain weight) per plant is the sole trait that selection does not appear to have improved in maize relative to teosinte. From a multivariate evolution perspective, we identified a strong, nonneutral divergence between teosinte and maize landrace genetic variance–covariance matrices (G-matrices). While the structure of G-matrix in teosinte posed considerable genetic constraint on early domestication, the maize landrace G-matrix indicates that the degree of constraint is more unfavorable for further evolution along the same trajectory.

Estimation of additive and dominance genetic variance components for female fertility traits in Iranian Holstein cows

The aim of the current study was to estimate additive and dominance genetic variance components for days from calving to first service (DFS), a number of services to conception (NSC) and days open (DO). Data consisted of 25 518 fertility records from first parity dairy cows collected from 15 large Holstein herds of Iran. To estimate the variance components, two models, one including only additive genetic effects and another fitting both additive and dominance genetic effects together, were used. The additive and dominance relationship matrices were constructed using pedigree data. The estimated heritability for DFS, NSC and DO were 0.068, 0.035 and 0.067, respectively. The differences between estimated heritability using the additive genetic and additive-dominance genetic models were negligible regardless of the trait under study. The estimated dominance variance was larger than the estimated additive genetic variance. The ratio of dominance variance to phenotypic variance was 0.260, 0.231 and 0.196 for DFS, NSC and DO, respectively. Akaike's information criteria indicated that the model fitting both additive and dominance genetic effects is the best model for analysing DFS, NSC and DO. Spearman's rank correlations between the predicted breeding values (BV) from additive and additive-dominance models were high (0.99). Therefore, ranking of the animals based on predicted BVs was the same in both models. The results of the current study confirmed the importance of taking dominance variance into account in the genetic evaluation of dairy cows.

Detection of epistasis through triple test cross (TTC) analysis in maize (Zea mays L.)

The present study was carried out to detect the epistasis present in two cross of maize through triple test cross (TTC) analysis. The mean squares due to total epistasis was highly significant at P≤0.01 for all the characters in both C-I and C-II, except for ear length in C-I. The i type of epistasis was highly significant for the traits such as days totasseling, days to silking, earlength, ear circumference, kernels row-1,100 grain weight and shelling percentage in C-I and in C-II, ‘i’ type was non-significant for ASI, ear length, kernels row-1and grain yield plot-1. Both j type and l type of epistasis were significant for all characters in both C-I and C-II, except for ear length in C-I and days to silking in C-II. The estimate of additive genetic component (D) was highly significant for all characters in both C-I and C-II. Epistasis played a significant role in the inheritance of all the characters in both C-I and C-II except for ear length in C-I. Both additive and dominance components of genetic variance with a predominance of dominance genetic variance played an important role in the inheritance of all the quantitative traits except ear length in C-I and kernel rows ear-1 in C-II.