GENERATION MEAN ANALYSIS FOR ESTIMATION SOME GENETIC PARAMETERS FOR YILD AND YIELD COMPONENTS IN FOURE MAIZE CROSSES.

A field experiment was conducted at the field of Field Crop .Dept., College of Agric\Univ.of Baghdad. spring and fall seasons of 2009, 2010 , spring of 2011 and fall of 2013 in order to know the relative magnitude of the genetic variation component and interactions forms of epistasis using Generation Means Analysis of maize (Zea mays L.) . Six generations P1 , P2 , F1 , F2, BC1 and BC2 for four crosses (FI01301 Rustico), (AntignaoHi39× Nostred ) , (Lo1391 ×Rustico) and ( Rusticocangini× Rustico) were evaluated by using randomized complete block design( RCBD) with four replications for grain yield and its components. The results showed significant differences between the generations of the four crosses. The first generation superiority and gave the highest mean for each of the traits of four crosses. The highest hybrid vigor and heterosis percent to for unit area grain yield (ton\ha) 121.8% and 126.92% for cross( FI01301 ×Rustico ). Most of the genetic effects (d additive , dominance h , additive × additive i , additive × dominance j and dominance × dominance l) were significant for all crosses . This revealed the importance of the dominance, additive and epistasis effects as genetic actions controlled in yield inheritance and its components in maize. But the dominance variation was more important than the additive variation in the ear length ,grain weighte and yield unit area, disagreement signal indicate the existence of an act of the dominance h and dominance× dominance l of most studied traits duplicate epistasis. Supplementary superiority also appeared to Epistasis complementary of crosses (FI01301×Rustico) and (AntignaoHi39×Nostred) and grain weight in cross (Lo1391 ×Rustico ). It can be conclude that the additive and non-additive gene action control the in heritable yield and its component . It is recommend using the method of reciprocal recurrent selection(RRS) to improve yield and its components .

An overview on quantitative and genomic tools for utilising dominance genetic variation in improving animal production

In addition to genetic progress made by selection on additive genetic values, short-term gains can be produced by recovering possible inbreeding depression or utilising putative overdominance. These are both caused mainly by dominance genetic variation which can be quantified using mixed model methodology. Inbreeding brings along a requirement for extra parameterisation in expressing and estimating dominance variance. The extra parameters specify how dominance is affecting the mean and (co)variances among inbred animals. The full description for breed crosses contains a very large set of parameters. The benefits from crossbreeding are highest with widely deviating allele frequencies between the breeds. Maximisation of heterosis can be done only on a temporary basis as a continued exploitation leads to stagnation in the overall genetic progress. Therefore efficient methods with immediate returns are needed to find the most promising breeds jointly with the most potential mating pairs. One possibility is the use of genomic tools in assessing populations for crossbreeding and in searching for major genes mediating dominance variation. The analyses are providing markers that can be used in choosing mating pairs that produce desirable dominance deviations in analysed marker brackets. Genome-wide marker sets can be used for discovering genome segments with maximum heterosis effect. The phenotypic records are available for such analyses, soon are also the large marker sets and their genotypes: the analytical tools need developers.;

Genetics of quality and agronomic traits in hard endosperm maize

SUMMARYHard endosperm maize (Zea mays L.) is useful for industry and for human consumption. The objective of the present work was to study the inheritance of quality traits in hard endosperm maize. Three flint and three dent inbreds, F1 of their diallel crosses, F2s and backcrosses to each parent were evaluated for grain yield and quality traits (flotation test, flour-milling test, grain damage (GD) index and grain density). Genotypes and genotype×environment interactions were significant for most traits. A genetic model including additive, dominance and epistatic effects explained most of the genetic variation for the traits. Additive effect mean squares were larger than those due to dominance effects, except for grain yield and GD. Partition of the dominance variance into average, general, and specific dominance components revealed that the average dominance related to heterosis was the most important. Additive×additive epistatic variation was smaller than additive and dominance variation for quality traits. Some inbreds displayed sufficient potential to be used in hard endosperm maize breeding programmes. The average dominance effect was favourable for most of the quality and agronomic traits. Breeding programmes for improving quality in hard endosperm maize would be most efficient if both additive and dominant effects are capitalized on.

Inheritance of High Sugars from Tomato Accession PI 270248 and Environmental Variation between Seasons

Small-fruited cherry tomato accession PI 270248 [Lycopersicon esculentum Mill. var. cerasiforme (Dunal) A. Gray] with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) (L. esculentum) that had normal (low) fruit sugars. The F1 was crossed to PI 270248 and 7833 to obtain BCP1 and BCP2, respectively, and self-pollinated to obtain F2 seed. The resulting population was used to study the inheritance of high sugars from PI 270248. Continuous sugar level frequency distributions of BCP1, BCP2, and F2 suggest that the trait is under polygenic control. Additive variation was significant, but dominance variation was not. There was a heterozygote × heterozygote type of epistasis present that likely caused the F1 sugar level to skew nearly to the level of the high sugar parent. The F2 mean sugar level was lower than the midparent level. Broad-sense heritability was 0.86. There was a significant line × season (fall, spring) interaction where lines with higher sugars were affected more by seasons than lines with lower sugars. Sugar level, in general, was higher in spring. Higher solar radiation in spring than in fall may explain the sugar level difference between the seasons.

Inbreeding and the Genetic Complexity of Human Hypertension

Considerable uncertainty exists regarding the genetic architecture underlying common late-onset human diseases. In particular, the contribution of deleterious recessive alleles has been predicted to be greater for late-onset than for early-onset traits. We have investigated the contribution of recessive alleles to human hypertension by examining the effects of inbreeding on blood pressure (BP) as a quantitative trait in 2760 adult individuals from 25 villages within Croatian island isolates. We found a strong linear relationship between the inbreeding coefficient (F) and both systolic and diastolic BP, indicating that recessive or partially recessive quantitative trait locus (QTL) alleles account for 10-15% of the total variation in BP in this population. An increase in F of 0.01 corresponded to an increase of ∼3 mm Hg in systolic and 2 mm Hg in diastolic BP. Regression of F on BP indicated that at least several hundred (300-600) recessive QTL contribute to BP variability. A model of the distribution of locus effects suggests that the 8-16 QTL of largest effect together account for a maximum of 25% of the dominance variation, while the remaining 75% of the variation is mediated by QTL of very small effect, unlikely to be detectable using current technologies and sample sizes. We infer that recent inbreeding accounts for 36% of all hypertension in this population. The global impact of inbreeding on hypertension may be substantial since, although inbreeding is declining in Western societies, an estimated 1 billion people globally show rates of consanguineous marriages >20%.