Showing 5 results for Genetic Parameters
Abdolamjid Rezai, Reza Amiri,
Volume 2, Issue 1 (4-1998)
Abstract
Diallel crosses among 6 Avena sativa L. and A. sterilis L. lines and introductions were used to evaluate the validity of the assumptions for the genetic model. Number of days to pollination, plant height at pollination and at maturity, as well as grain and stem protein percentages were evaluated. According to Griffing's method 1 the reciprocal mean squares for all the traits under study were significant. But based on Hayman's analysis, the maternal effects for all the traits studied were not significant. Therefore, reciprocal means were used to evaluate the validity of the absence of multiple alleles, linkage and epistasis effects using regression of Wr on Vr and analysis of variance for Wr + Vr and Wr - Vr. Based on the results of the 3 methods, the genetic models for plant height at maturity and days to pollination were unbiased. Therefore, Hayman's analysis was used to estimate the genetic parameters for these traits. For plant height at pollination and stem protein percentage, significant and nonsignificant differences of regression slope from one and zero (Ho: β = 1 and Ho: β = 0) were detected, respectively. For these traits the biasedness of the model was removed after elimination of one parent from the diallel table. Grain protein percentage was not analyzed as it necessitated the elimination of 2 parents from the diallel table. In general, regression of Wr on Vr compare to Wr + Vr and Wr - Vr analysis of variances showed to be a more valid inductive method for testing the accuracy of the genetic model assumptions. Also, results of the Hayman and Jinks analysis, both when the assumptions are valid and when not, showed that genetic parameters are affected by the biasedness of the model, and that different estimates will be obtained. The Griffing's method was less affected by the unbiasedness of the model than Hayman and Jinks method. Therefore, it seems that preliminary testing for validity of the assumptions is necessary in Hayman and Jinks genetic model.
M. R. Bahreini Behzadi, F. Eftekhari Shahroudi, L. D. van Vleck,
Volume 9, Issue 1 (4-2005)
Abstract
Data from the birth weight (BW), the average daily gain from birth to weaning (ADG) and the weaning weight (WW) of 1182, 1099 and 1099 lambs were respectively collected and applied to estimate the maternal effects on heritabilities as well as on the determination of the environmental factors. The data were collected from Shahrbabak Sheep Breeding Research Station within five year, from 1993 to 1998. The effects of the year of birth, the age of the dam and its sex on all the traits were significant. The type of birth had no effect on BW but it was significant for the other two traits. Estimates of (co)variance components and genetic parameters were obtained by restricted maximum likelihood, using single and two-trait animal models. Based on the most appropriate fitted model, direct heritability of BW, ADG and WW were estimated at 0.10± 0.06, 0.21 ±0.08 and 0.22± 0.09, respectively. The maternal heritability for the three traits was also estimated at 0.27± 0.04, 0.15 ±0.05 and 0.19 ±0.05, respectively. Direct genetic and phenotypic correlations between BW and ADG BW and WW ADG and WW were estimated at 0.85 and 0.41 0.82 and 0.48 and 0.99 and 0.99, respectively. Ignoring maternal effects in animal model caused overestimation of direct heritability. Thus maternal effects are significant sources of variation for early growth traits and their ignorance in the animal model causes inaccurate genetic evaluation of the lambs.
S. R. Miraei Ashtiani, P. Zamani, A. Nikkhah, M. Moradi Shahrbabak, A. Naserian, F. Akbari,
Volume 9, Issue 4 (1-2006)
Abstract
Improvement of feed efficiency in dairy farming economically has a great importance. In this study, the genetic parameters of net energy efficiency and its relationships with milk yield, 3.2% fat corrected milk, body weight, gross income and income over feed costs were investigated, by the 2589 monthly records collected from the 723 lactating cows in the 3 herds. The different requirements of energy were estimated, by the National Research Council (NRC) models. A general linear model was employed for determining significant factors affecting each trait. The genetic parameters were estimated by a multivariate analysis with the derivative free approach of restricted maximum likelihood algorithm. The animal models contained the fixed effects of herd-year-season, parity number and stage of lactation, the regression coefficients of each trait on the dietary levels of rumen undegradable protein and metabolizable energy, and the random effects of animal additive genetic, permanent environment and residuals. The heritability of milk yield, 3.2 percent fat corrected milk, body weight, net energy efficiency, gross income and income over feed cost, were estimates 0.31, 0.32, 0.30, 0.34, 0.24 and 0.29 respectively. The results of this study indicated that the direct selection for net energy efficiency might genetically improve the feed efficiency. It also seems that the selection for fat corrected milk may be effective for the indirect improvement of feed efficiency and economic performance of dairy cows.
M. Tousi Mojarrad, M.r. Ghannadha,
Volume 12, Issue 43 (4-2008)
Abstract
In order to study inheritance of traits (Height, Peduncle length, Extrusion peduncle length, Diameter first internode, Diameter secondary internode, Diameter third internode length of secondary internode, length of third internode) associated with height in bread wheat, seven cultivars of bread wheat with their F1 progenies produced through a half diallel mating design were planted in a randomized complete block design with 3 replications in normal and drought conditions in the Seed and Plant Improvement Institute, Karaj, in 2004. Analysis of variance showed significant differences for all the traits in normal and drought conditions at 1 % probability level. Diallel analysis showed that general combining abilities were significant for all the traits in normal and drought conditions at 1% level of probability. The specific combining abilities were not significant except for extrusion peduncle length and length of secondary internode. Additive effect was more important in controlling all the traits. Height had the most broad sense and narrow sense heritabilities in normal and drought conditions. It was also found that increasing all the traits except for plant height and length of the third internode was controlled by the dominance alleles in normal and drought condition. The analysis of traits revealed more mean traits in progenies compared to parents in both normal and drought conditions. Sardary and Roshan varities showed the best general combining ability in normal and drought conditions.
H. Naeemipour Younesi, H. Farhangfar , M.r. Asghari,
Volume 12, Issue 43 (4-2008)
Abstract
A total of 1256 records associated with body weight and Cashmere at different ages (birth and 3 and 9 months) obtained from 754 Cashmere goats were used to estimate the genetic parameters in southern Khorasan province during 2000- 2003. A set of univariate animal models including additive and maternal genetic effects and maternal permanent environmental effects as well as the fixed effects of year and month of birth, sex, birth type and dam age (linear and quadratic covariates) and kid age (linear and quadratic covariates) was fitted. Co/variance components were estimated by restricted maximum likelihood procedure using Powel algorithm in DFREML software. For the body weight at 0, 3 and 9 months, models two, one and three were recognized as the appropriate models. For these models, direct heritability estimates were found to be 0.09, 0.11 and 0.09, respectively. For birth weight and weight at month 9, the magnitude of c2 and h2m were 0.18 and 0.00, respectively. For average daily gains during 0-3 and 3-9 months of age, direct heritability based on the model one was 0.16 and 0.05, respectively. Direct heritability of Cashmere was found to be 0.02. Applying repeatability model, the estimates of heritability and repeatability of Cashmere were 0.16 and 0.53, respectively. Genetic trends for birth weight (0.0175kg/year) and weight at month 9 (0.02065kg/year) were positive and non-significant. A negative non-significant statistical genetic trend (-0.00537kg/year) was found for Cashmere during the period of time.
