Line and crossing effects in a diallel mating system with highly inbred lines of White Leghorn chickens

Summary Seven highly inbred lines of White Leghorn chickens were used in a near complete diallel mating plan during eight years. The lines originated from three different base populations selected for egg weight. Average inbreeding coefficients of parents of chicks hatching in successive years were 0.75, 0.80, 0.84, 0.86, 0.89, 0.91, 0.93 and 0.94. The composition of line, specific combining ability and reciprocal effects and their estimated values are given. These effects were estimated for age at first egg (AFE), average weight of all eggs laid to 40 weeks (EW40), body weight at 40 weeks (BW40), number of eggs to 40 weeks (EP40) and number of eggs between 41 and 60 weeks (EP60). Records of 3247 hens surviving to 40 weeks and of 3133 birds to 60 weeks could be used. Large differences between line effects could be found in all traits. They were only partly due to the preceding selection in the base populations. All specific combining effects were in the expected direction, negative for AFE and positive for EW40, BW40, EP40 and EP60. Recovery of inbreeding depression inflated these effects rather substancially. Average heterosis, defined as the relative superiority of a line combination over the mid parent value, was –11.3%, 5.8%, 7.8%, 45.1% and 35.8% for AFE, EW40, BW40, EP40 and EP60 respectively. One line showed a relative superiority in AFE of -19.3% compared to about –7.9% for all other combinations. Reciprocal or sex-linked effects were generally smaller in all traits than specific combining effects, they were considerably smaller in AFE, EP40 and EP60. General reciprocal effects could be found for several lines in one or more traits. Offspring of two lines, when used as sire lines, showed a negative correlation between reciprocal effects of egg weight and body weight.     

Effects of pollen donors on seed formation inEspeletia schultzii (Compositae) populations at different altitudes

The influence of different pollen donors on seed formation was investigated in three populations ofEspeletia schultzii that differ in environmental conditions and life history characteristics. Self pollen and pollen from different donors (< 15m apart) within each population was used in a diallel design in order to test the genetic base of seed set variation. Three measures of seed formation were used: (1) achene number; (2) proportion of filled achenes (fruits) that distinguishes between achenes with seeds and empty achenes; (3) proportion of aborted seeds that distinguishes between viable and aborted seeds. Self-pollinations resulted in empty achenes. Achene number did not vary between the different pollen donors. A bimodal pattern of filled achenes was found in two populations in two consecutive years. On the other hand, a unimodal pattern was found in crosses between more distant donors (> 30m). These patterns seems to be the results of a sporophytic incompatibility system. Seed abortion was highest at the higher elevations and seems to be correlated with elevation rather than with any genetic effect.     

Diallel analysis for sex-linked and maternal effects

Genetic models including sex-linked and maternal effects as well as autosomal gene effects are described. Monte Carlo simulations were conducted to compare efficiencies of estimation by minimum norm quadratic unbiased estimation (MINQUE) and restricted maximum likelihood (REML) methods. MINQUE(1), which has 1 for all prior values, has a similar efficiency to MINQUE(), which requires prior estimates of parameter values. MINQUE(1) has the advantage over REML of unbiased estimation and convenient computation. An adjusted unbiased prediction (AUP) method is developed for predicting random genetic effects. AUP is desirable for its easy computation and unbiasedness of both mean and variance of predictors. The jackknife procedure is appropriate for estimating the sampling variances of estimated variances (or covariances) and of predicted genetic effects. A t-test based on jackknife variances is applicable for detecting significance of variation. Worked examples from mice and silkworm data are given in order to demonstrate variance and covariance estimation and genetic effect prediction.     

双列杂交F1代加倍单倍体的遗传模型

双列杂交法已广泛地应用于性状的遗传研究,但均局限于无非等位基因互作的性状．本文在前人研究的基础上提出了应用双列杂交F_1代加倍单倍体检验双基因互作模型适合性的方法,并对遗传参数的估算作了进一步的研究．     

Diallel analysis of androgenetic plant production in hexaploid Triticale (X. triticosecale,Wittmack)

Summary Studies were made on the genetic determination of androgenetic plant yield and its two components: embryo production and green plant regeneration. This involved the analysis of a complete 7×7 diallel cross of 4 androgenetic lines and 3 lines obtained by pedigree selection, one of them having the Triticum timopheevi cytoplasm. The three traits analysed are both heritable and environmentally influenced (by season and culture medium composition). The analysis of embryo production shows a mainly nuclear inheritance, with predominantly additive gene action, but also a favourable effect of Triticum timopheevi cytoplasm. Green plant regeneration has a more complex genetic determination, with additive as well as non-additive gene action and cytoplasmic influences. Hybrids appear superior to inbred lines for embryogenesis and green plant yield, but not for green plant regeneration. Androgenetic lines used as parents did not show superiority over other parents either in their own value or in the transmission of androgenetic abilities. Genetic improvement seems to be possible by recombination in progenies of hybrids between lines having complementary abilities.     

Combining abilities and heritability of callus formation and plantlet regeneration in wheat (Triticum aestivum L.) anther cultures

Summary Frequency of callus formation in wheat (Triticum aestivum L. em. Thell) anthers cultured in vitro and the frequency of subsequent plantlet formation from such calli were examined in a diallel population produced from five inbred spring wheat cultivars. Two of the five cultivars were believed to possess relatively high frequencies of response and the other three relatively low response frequencies, based on previous studies. General and specific combining abilities were estimated and found to be highly significant for both traits. Reciprocal effects were also estimated and were highly significant for both traits. Of the 25 entries, the largest mean callus formation frequency was observed on anthers of Kitt x Olaf, while the largest mean plantlet formation frequency was observed using anthers of the cultivar, Fielder. No significant correlation was observed between the two traits. Heritability estimates in the range of 0.6–0.7 suggested, however, that both traits were highly heritable, so that rapid gain from selection for these traits should be possible. Current limitations due to genetic variation in responses therefore may not constitute a major obstacle to application of in vitro techniques by wheat breeders.Scientific Article No. 3710 Contribution No. 6686 of the Maryland Agric. Exp. Stn., Dept. of Agronomy, College Park, MD 20742, and USDA-ARS, Beltsville, MD 20705, USA     

Limits of artificial selection under unbalanced mating systems

Summary The influence of unbalanced mating systems — factorial mating (FM) and random loss of families after a full diallel crossing (RS) — on the ultimate probability of gene fixation (u()) and the time required to fix or lose a gene (t()) are investigated. The average u() of these systems is smaller than that of random mating, and the range of u() for a given initial parental genotype combination is very large (close to one for most initial genotypic combinations). The average u() of different parental genotypic combinations of a given gene frequency are different. These systems accelerate the t().This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain     

Combining ability and parental evaluation in five selected clones of sugarcane (Saccharum sp. hybrids)

Summary Five Hawaiian commercial sugarcane (Saccharum sp. hybrids) clones were crossed in a full diallel. Four morphological characters were studied in the progeny: number of millable stalks per plant, stalk diameter, stalk length, and sucrose content. A fifth character, plant volume, was calculated from stalk number, stalk diameter and stalk length. The five selected parental clones were treated as fixed variables in the analysis. General combining ability (gca) was significant for all five characters; specific combining ability (sca) was significant for stalk diameter, stalk length, and plant volume. The variance for gca was large in all progeny populations. However, the variance for sca was large in the progeny of only some clones and/or for some individual characters. Parents were evaluated on the basis of their general combining ability: clone H49-3533 had high gca for sucrose content, while clone H53-5356 had high gca for plant vigor.Published with the approval of the Director as Journal Series Paper No. 455, Experiment Station, Hawaiian Sugar Planters' Association.     

Diallel analysis for some quantitative characters in Petunia hybrida Hort

Summary Flowering time, plant height and flower size in Petunia hybrida Hort. (multiflora type) have been genetically analysed by means of a 5 × 5 diallel cross. The results indicated that: (1) the three characters are controlled by additive-dominance polygenic systems. The contribution of the additive gene actions to the genetic variance of flowering time was relatively higher than that of dominance. The reverse situation was found for plant height and flower size. (2) Dominance is ambi-directional for the three characters. Ratios of average dominance were in the range of partial for flowering-time, complete for plant height and overdominance for flower size. (3) Number of genes (or gene groups) controlling the characters are about 3, 3 and 5 for flowering time, plant height and flower size: respectively, (4) Heritability estimates are 0.84, 0.88 and 0.89 in the broad-sense and 0.40, 0.49 and 0.37 in the narrow-sense, for flowering time, plant height and flower size; respectively. (5) Heterosis as percent increase of the mean F₁-hybrid above the higher parent, or decrease below the lower parent, was observed for flowering time (+ 9.7% to +13.3%), for plant height (–13.6% to –20.3%) and for flower size (+2.5% to +16.0%).     

A general framework for marker-assisted selection

Early simulation studies have showed that the inclusion of epistatic components (especially the additive-by-additive effects) into marker-assisted selection (MAS) can improve selection efficiency for a short-term breeding program. In this study I extend Lande and Thompson's theory to incorporate both additive and non-additive effects into MAS with reference to the mass selection case. Four different indices are analytically examined in terms of the type of genetic components involved in the marker scores: phenotype-, general combining ability (GCA)-, and GCA and reciprocal effects-based marker scores. The phenotype-based marker index is applicable to any population of non-random mating, while the other three indices are applicable to the synthetic population derived from diallel crosses. All these indices may have higher selection efficiencies than the index with solely additive effects-associated markers as long as the detectable transient non-additive effects are present. The improvement in selection efficiency depends on the magnitude of non-additive variances and the proportion of them explained by markers. The index with the phenotype-based marker scores operates on the whole of the additive and non-additive effects, and has the largest selection efficiency. The indices with the GCA-based marker scores operate only on additive and additive-by-additive genetic variation and have relatively small selection efficiencies. Inclusion of the markers from organelle genomes can also increase selection efficiency, depending upon the proportion of the total genetic variation attributable to organelle genomes and the proportion of them explained by organelle genomic markers. Sharing of markers among different marker scores does not facilitate the improvement of selection efficiency.