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Abstract: Triticum turgidum L var. durum is known to be particularly susceptible to infection by Fusarium graminearum, the causal agent for Fusarium head blight (FHB), which results in severe yield [...]

The changes in the mean and variance components of a quantitative trait caused by changes in allele frequencies, concentrating on the effects of genetic drift are analyzed. Random drift generates transient linkage disequilibria that cause correlations between allele frequency fluctuations at different loci.

The objective was to estimate breed, heterosis, and recombination effects on pig reproductive traits in two different four-breed composite populations. Breeds included Yorkshire, Landrace, Large White, and Chester White in Exp. 1 and Duroc, Hampshire, Pietrain, and Spot in Exp. 2. Data were recorded on purebred pigs, two-breed cross pigs, and pigs from generations [F.sub.1] through [F.sub.6], where [F.sub.1] pigs were the first generation of a four-breed cross. Litter traits were considered a trait of the gilt. There were 868 first parity litters in Exp. 1 and 865 in Exp. 2. Direct heterosis significantly increased sow weight at 110 d of gestation and litter weight at 14 and 28 d (weaning) in both experiments. Direct heterosis significantly increased number of nipples, weight at puberty, lactation weight loss, litter size, and litter birth weight in Exp. 2. Gestation length in Exp. 1 and age at puberty in Exp. 1 and Exp. 2 were significantly decreased by direct heterosis. Maternal heterosis significantly increased age at puberty in Exp. 2 and decreased sow weight at 110 d of gestation in Exp. 1. Recombination significantly increased sow weight at 110 d of gestation and tended to increase total number born and litter birth weight in Exp. 1. Recombination significantly decreased age at puberty in Exp. 2. Litter heterosis significantly increased number of pigs at 14 and 28 d; litter weights at birth, 14, and 28 d; and tended to increase lactation weight loss in Exp. 1. Litter heterosis decreased litter size in Exp. 2. Maternal heterosis and recombination effects had a sampling correlation of -0.97 in Exp. 1 and -0.91 in Exp. 2 for number of fully formed pigs. Therefore, maternal heterosis and recombination effects were summed, and their net effect was tested. This net effect tended to increase number of nipples, lactation weight loss, and litter birth weight and significantly increased number of fully formed pigs in Exp. 1. Direct, maternal, and litter heterosis and recombination effects significantly influenced reproductive traits. Key Words: Cytoplasm, Epistasis, Pigs, Recombination, Reproduction, Variance Components

The primary objective was to estimate breed, heterosis, and recombination effects on growth and carcass traits of two different four-breed composite populations of pigs. Experiment 1 (Exp. 1) included purebred and crossbred pigs originating from York-shire, Landrace, Large White, and Chester White breeds, and Experiment 2 (Exp. 2) included pigs from Duroc, Hampshire, Pietrain, and Spot breeds. Data were recorded on purebred pigs, two-breed cross pigs, and pigs from generations [F.sub.1] through [F.sub.6], where [F.sub.1] pigs were the first generation of a four-breed cross. Pig weights were recorded at birth and at 14, 28, 56, 70, and 154 d of age. Average daily gain was calculated for intervals between weights, and ultrasonic backfat measurements (A-mode) were taken at 154 d of age. Feed intake was measured between 70 and 154 d of age on mixed pens of boars and barrows. Carcass backfat, length, and loin muscle area were measured on barrows at slaughter. Mixed-model analyses were done separately by experiment, fitting an animal model. Fixed effects included farrowing group and sex for growth traits and farrowing group for carcass traits. For ADFI, a weighted mixed-model analysis was done fitting farrowing group as a fixed effect, sire nested within farrowing group as a random effect, and weighting each observation by the number of pigs in each pen. To test feed efficiency, a second analysis of ADFI was done adding ADG as a covariate in the previous model. Included as covariates in all models were direct, maternal, and maternal grandam breed effects, direct and maternal heterosis effects, and a direct recombination effect. Recombination is the breakup of additive x additive epistatic effects present in purebreds during gamete formation by crossbred parents. Effects of direct heterosis significantly increased weights at birth, 14, 56, 70, and 154 d of age in Exp. 1. Effects of direct heterosis significantly increased ADG from birth to 14, 28 to 56, and 70 to 154 d of age in Exp. 1. In Exp. 2, effect of direct heterosis significantly increased weights and ADG at all ages. In Exp. 1, recombination significantly reduced loin muscle area. In Exp. 2, recombination significantly increased weights at birth, 14, 28, and 56 d, ADFI from 70 to 154 d, and ADFI adjusted for ADG. The correlation between maternal heterosis and recombination effects for all traits in Exp. I and Exp. 2 was approximately -0.90. Maternal heterosis and recombination effects were estimable, but greatly confounded. Key Words: Correlation, Cytoplasm, Epistasis, Pigs, Recombination, Variance Components

Research shows that in the mouse embryo the multipass membrane protein Smoothened, involved in Hedgehog signaling, acts epistatic to Ptc1 to facilitate Shh and Ihh signaling. Data further show that Hedgehog signaling within the mouse node determines left/right asymmetry.

Research examines geographic origin of Rhexia, belonging to the family of Melastomeae, based on the chloroplast gene ndhF and a fossil-calibrated clock. Results indicate that Melastomeae once ranged from Eurasia to North America and subsequently spread to South America, Africa, and Southeast Asia, with eventual extinction due to climate deterioration.

Research discusses Dobzhansky-Muller incompatibilities in relation to hybrid sterility and inviability caused by the stochastic accumulation of substitutions in the genomes of species constituting hybrids. Results show that probability of two divergent species contributing to hybrid sterility or inviability is very small as revealed by Drosophila and Bombina flies.

The role of multiplicative gene action in producing heterosis was elucidated. Multiplicative effects between non-alleles give rise to epistatic effects of the additive by additive type. Heterosis may be partitioned into a dominance effect component and an additive by additive-epistasis component. Heterosis with multiplicative actions involve both the dominance components as well as the multiplicative interactions. However, heterosis without dominance may also arise from multiplicative as wellas other nonadditive effects between loci. Multiplicative action may make increase dominance effects. Further discussions on the genetic role of multiplicative effects are discussed.

Strains of Drosophila melanogaster that carry nine mtDNAs of varying molecular divergence from within the D. melanogaster species subgroup in combination with two D. melanogaster nuclear genomes were generated to test for within- and between-species mitochondrial nuclear interactions. The findings revealed that a low mitochondrial substitution rate, resulting from a low mutation rate and/or efficient purifying selection, prohibits the accumulation of mitochondrial-nuclear incompatibilities among the studied Drosophila species.

Crossed combinations of mitochondrial and nuclear lineages of the seed beetle Callosobruchus maculatus and assay metabolic rate under two different temperature regimes are utilized to understand the intergenomic epistasis between mitochondrial and nuclear genes that might affect whole-organism metabolic phenotypes. The results provide insight into the mtDNA sequence variation linked to whole-organism metabolic rate and mechanism and the possible role of mtDNA in life-history of evolution, particularly in thermal adaptation.

Concepts from the formal theory of information to calculate the amount of genomic information that could be maintained is used to identify conditions under which much higher levels of genomic information could be maintained compared to previously considered origin-of-life researchers. The findings revealed that the highest levels of information could be maintained when many genotypes produce identical phenotypes and when reproduction occasionally involves recombination between multiple parental genomes.

The article presents a new methodology, which can be used for the measurement of fitness while considering fitness as a measure of competitive ability. The significance of the measurement theory of fitness for measuring the gene interaction with respect to fitness is also determined.

The direction and magnitude of epistatic interactions in a polygenic trait under stabilizing selection were examined to determine their influence on the evolution of hybrid incompatibilities. A possible hypothesis for polygenetic drift explained the evolution of postzygotic reproductive isolation which evolves due to the accumulation of incompatible epistatic interactions.

A study examines the nature and dominance of epistasis between alleles derived from Drosophila persimilis which causes hybrid male sterility in the genetic background of its sister species Drosophila pseudoobscura, in order to assess its key role in causing hybrid incompatibilities. Results reveal that epistasis increases the dominance of individually recessive-acting QTL loci so that they play a role in hybrid male sterility.

Several simulation studies are conducted to determine the levels of inversions and genesE impact on the adaptive divergence observed within the chromosomal inversions. The results prove that the inversions play an extremely significant role in the maintenance of the species.

The impact of different latitudinal and cold-tolerance conditions on the DNA repeat-number variation in the hsr-omega RNA gene of Drosophila melanogaster is discussed. The repeat number is shown to exhibit a negative relationship with the cold tolerance of the species.

Several multi-trait experiments are conducted to present a comparative study of the importance of pleiotropy and signaller-receiver genes epistasis in the life-history of trade-offs. The signaller-receiver epistases are shown to create trade-offs among the multiple correlated traits affecting fitness.

A study was conducted to map epistatic endosperm trait loci (ETL) under a triploid genetic model of endosperm traits in a random hybridization design. The proposed method is verified by a series of Monte Carlo simulation experiments.

A study was conducted to assess the influence of hybridization on patterns of preferences for parental type odorant mate signals across a unimodal hybrid zone between two European subspecies of the house mouse, Mus musculus musculus and M. m. domesticus. The study provides first indirect information on a possible genetic determination of preference in a mammal and the involvement of a polygenic autosomal system with dominance and epistasis.

The quantitative loci study is conducted to explain the contribution of differential epistasis on the variation observed in the allometric relationship that exists between the long bone lengths and body weight in a mouse. The epistasis is found to ultimately lead to genetic variations in pleiotropy.

The contribution of additive, dominance and epistatic genetic effects to the differentiation in oviposition preference between two populations of the seed beetle Acanthoscelides obtectus evolved in the laboratory on bean and chickpea seeds are investigated. The results have shown a positive effect of epistasis on the performance of the second generations of hybrids.

Studies, in which the level of genetic variation in experimentally inbred populations was compared with that in outbred control populations, show that high-quality genetic variation is lost and low-quality variation is gained during periods of small population size. A loss of fitness is expected because expressed characters will be displaced away from selective optima and implies that life-history traits are underlain by substantial dominance or epistasis.

The levels of epistasis in crosses between populations of two contrasting sibling species, D. serrata and D. birchii Dobzhansky and Mather are compared. The result shows that strong epistasis has not developed among the D. birchii populations and the habitat specialist does not show stronger epistasis than D. serrata, thus it points to epistasis not being directly linked to divergence times among populations.

An approximate solution for the mean fitness in mutation-selection balance with arbitrary order of epistatic interaction is derived. The solution is based on the assumptions of coupling equilibrium and that the interaction effects are multilinear. We find that the effect of m-order epistatic interactions (i.e., interactions among groups of m loci) on the load is dependent on the total genomic mutation rate, U, to the mth power. Thus, higher-order gene interactions are potentially important if U is large and the interaction density among loci is not too low. The solution suggests that synergistic epistasis will decrease the mutation load and that variation in epistatic effects will elevate the load. Both of these results, however, are strictly true only if they refer to epistatic interaction strengths measured in the optimal genotype. If gene interactions are measured at mutation-selection equilibrium, only synergistic interactions among even numbers of genes will reduce the load. Odd-ordered synergistic interactions will then elevate the load. There is no systematic relationship between variation in epistasis and load at equilibrium. We argue that empirical estimates of gene interaction must pay attention to the genetic background in which the effects are measured and that it may be advantageous to refer to average interaction intensifies as measured in mutation-selection equilibrium. We derive a simple criterion for the strength of epistasis that is necessary to overcome the twofold disadvantage of sex.

In general, common diseases do not follow a Mendelian inheritance pattern. To identify disease mechanisms and etiology, their genetic dissection may be assisted by evaluation of linkage in mouse models of human disease. Statistical modeling of multiple-locus linkage data from the nonobese diabetic (NOD) mouse model of type 1 diabetes has previously provided evidence for epistasis between alleles of several Idd (insulin-dependent diabetes) loci. The construction of NOD congenic strains containing selected segments of the diabetes-resistant strain genome allows analysis of the joint effects of alleles of different loci in isolation, without the complication of other segregating Idd loci. In this article, we analyze data from congenic strains carrying two chromosome intervals (a double congenic strain) for two pairs of loci: Idd3 and Idd10 and Idd3 and Idd5. The joint action of both pairs is consistent with models of additivity on either the log odds of the penetrance, or the liability scale, rather than with the previously proposed multiplicative model of epistasis. For Idd3 and Idd5 we would also not reject a model of additivity on the penetrance scale, which might indicate a disease model mediated by more than one pathway leading to [Beta]-cell destruction and development of diabetes. However, there has been confusion between different definitions of interaction or epistasis as used in the biological, Statistical, epidemiological, and quantitative and human genetics fields. The degree to which statistical analyses can elucidate underlying biologic mechanisms may be limited and may require prior knowledge of the underlying etiology.

Sex is thought to facilitate accumulation of initially rare beneficial mutations by allowing simultaneous allele replacements at many loci. However, this advantage of sex depends on a restrictive assumption that the fitness of a genotype is determined by fitness potential, a single intermediate variable to which all loci contribute additively, so that new alleles can accumulate in any order. Individual-based simulations of sexual and asexual populations reveal that under generic selection, sex often retards adaptive evolution. When new alleles are beneficial only if they accumulate in a prescribed order, a sexual population may evolve two or more times slower than an asexual population because only asexual reproduction allows some overlap of successive allele replacements. Many other fitness surfaces lead to an even greater disadvantage of sex. Thus, either sex exists in spite of its impact on the rate of adaptive allele replacements, or natural fitness surfaces have rather specific properties, at least at the scale of intrapopulation genetic variability.