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At least 19 recordsLinked to original sources
PubMed1992

Phenotypic plasticity for life-history traits in Drosophila melanogaster. III. Effect of the environment on genetic parameters.

We estimated genetic and environmental variance components for developmental time and dry weight at eclosion in Drosophila melanogaster raised in ten different environments (all combinations of 22, 25 and 28 degrees C and 0.5, 1 and 4% yeast concentration, and 0.25% yeast at 25 degrees C). We used six homozygous lines derived from a natural population for complete diallel crosses in each environment. Additive genetic variances were consistently low for both traits (h2 around 10%). The additive genetic variance of developmental time was larger at lower yeast concentrations, but the heritability did not increase because other components were also larger. The additive genetic effects of the six parental lines changed ranks across environments, suggesting a mechanism for the maintenance of genetic variation in heterogenous environments. The variance due to non-directional dominance was small in most environments. However, there was directional dominance in the form of inbreeding depression for both traits. It was pronounced at high yeast levels and temperatures but disappeared when yeast or temperature were decreased. This meant that the heterozygous flies were more sensitive to environmental differences than homozygous flies. Because dominance effects are not heritable, this suggests that the evolution of plasticity can be constrained when dominance effects are important as a mechanism for plasticity.

Adaptation, Physiological↗
PubMed1992

Estimation of genetic parameters for somatic cell score in Holsteins.

Genetic parameters of somatic cell scores for Holstein cows were estimated using an animal model and REML for two data sets. Set 1, with 13,017 records from 5278 cows, was used to obtain variance components, heritability, and repeatability for two lactation measures: the simple average and the weighted average of test day data. Set 2, with 14,418 records from 4806 cows, was used to obtain genetic correlations for the simple average between lactations 1 and 2, between lactations 1 and 3, and between lactations 2 and 3. Simple and weighted average of test day somatic cell scores had the same heritabilities (.12) and repeatabilities (.35). Phenotypic variances were about 1.2, and herd-sire interaction variances were small (.002). Genetic correlation for somatic cell score was about .55 between lactations 1 and 2 and between lactations 1 and 3 and .65 between lactations 2 and 3. Phenotypic correlation was .20 between lactations 1 and 2, .16 between lactations 1 and 3, and .31 between lactations 2 and 3.

Animals↗
PubMed1975

Efficient experimental designs for the estimation of genetic parameters in plant populations.

Procedures for estimating the genetic parameters of plant populations frequently employ progeny testing to ascertain the genotype of maternal plants. However, when experimental resources are limited (e.g., electrophoretic markers), the large progeny sizes required for accurate typing severely restricts the numbers of families which can be tested. In this paper, four experimental designs with partial progeny testing are compared with the standard procedure of complete testing for their statistical efficiency in estimating the gene frequency, fixation index, and outcrossing rate at a single diallelic locus. It is shown that substantial increases in efficiency can be obtained (especially in inbred populations) if one or two individuals per family are assayed, and then further progeny testing is confined to those families which give rise to a heterozygote in this initial screening. Sample size for various purposes are computed and factors affecting the applicability of such "censored" designs are discussed.

Female↗
PubMed1992

Genetic parameters of conformation traits, milk yield, and herd life in Holsteins.

Genetic parameters were estimated simultaneously for 5 herd-life traits, 15 conformation (type) traits, and milk yield measured in first lactation for 128,601 Holstein cows. Heritabilities of all traits were higher in registered than in grade cows. Genetic correlations of linear type traits with first lactation yield ranged from -.48 for udder depth to .54 for dairy form. Genetic correlations among milk yield and herd-life traits were all positive except for milk-corrected herd life in grade cows. Udder traits had largest absolute genetic correlations with herd-life traits, followed by body traits and feet and leg traits. Some traits associated with body size and foot angle differed between registered and grade cows. Estimates of genetic trends from obtained parameters revealed greatest progress for milk yield from single-trait selection but also the largest changes for some type traits and milk-corrected herd life in an undesirable direction. Relative milk to type ratios of between 2:1 and 3:1 yielded 90% of the gain in milk yield with no change or slight improvement in type traits and functional herd life. Selection for type traits associated with herd life appears to be warranted to improve days of functional herd life or to decrease involuntary culling of dairy cows.

Animals↗
PubMed1977

Estimates of genetic parameters of body weight in descendants of X-irradiated rat spermatogonia.

Effects of nine generations of 450r per generation of ancestral spermatogonial X irradiation of inbred rats on genetic parameters of body weight at 3, 6, and 10 weeks of age and of weight gains between these periods were studied. Covariances among relatives were estimated by mixed model and regression techniques in randomly selected lines with (R) and without (C) radiation history. Analyses of the data were based on five linear genetic models combining additive direct, additive indirect (maternal), dominance and environmental effects. Parameters in these models were estimated by generalized least-squares. A model including direct and indirect genetic effects fit more closely to the data in both R and C lines. Overdominance of induced mutations did not seem to be present. Ancestral irradiation increased maternal additive genetic variances of body weights and gains but not direct genetic variances. Theoretically, due to a negative direct-maternal genetic correlation, within full-sib family selection would be ineffective in increasing body weight at six weeks in both R and C lines. However, progress from mass selection would be expected to be faster in the R lines.

Aging↗
PubMed1992

Estimation of changes in genetic parameters in selected lines of mice using REML with an animal model. 2. Body weight, body composition and litter size.

Restricted Maximum Likelihood (REML) with an animal model was used to estimate genetic parameters of body weight, body consumption and litter size of lines of mice selected for 20 generations on an index of lean mass at 10 weeks in males, highly correlated with body weight, and for a further 18 generations on body weight at 10 weeks in males and females. Univariate and multivariate estimates of heritability were about 0.5 and those of common environment correlations were about 0.25 for both body weight and composition. Body weight and fat pad weight had genetic and phenotypic correlations of about 0.5. The heritability estimate of litter size was about 0.15 from univariate analysis, rather lower from multivariate, and the estimate of its genetic correlation with body weight was about 0.25. There were reductions in heritability of both body weight and litter size in later generations, even though full pedigrees were fitted and inferences made to the base population, but a plateau in response to selection for increased body weight could not be explained by a complete attenuation of genetic variance.

Animals↗
PubMed1992

[Iterative estimation of variance components for a mixed model with a numerator relationship matrix: apply to compute K of variance ratio in BLUP and genetic parameters].

An iterative procedure is presented for the estimation of variance components in the mixed model with a numerator relationship matrix from non-balanced data. This method has been shown to be feasible if only designing matrix for fixed effects of the mixed model and Henderson method 3 hypothetic condition of the fixed effect to compute correctly the reduction in sum of squares, we would obtain more precise estimation of variance components, furthermore, the sizes of the initial value K could not affect to last result of the iterative solution. This is because in the iterative process may adjust automatically by designing matrix. Also, the variance components could apply not only to compute variance ratio in BLUP, but also to estimate genetic parameters.

Animals↗
PubMed1992

Increased litter size in Rambouillet sheep: I. Estimation of genetic parameters.

The variance and covariance components needed to estimate heritabilities of and genetic correlations among litter size, ovulation rate, scrotal circumference, and BW in a flock of Rambouillet sheep were estimated using REML via an expectation-maximization type algorithm. The heritability estimates from univariate analyses were .14, .21, .25, .36, and .15 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively, and average heritability estimates from bivariate analyses were .19, .20, .20, .34, and .10 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively. The genetic correlation between litter size and ovulation rate was near unity. Body weight in ewes had a moderate genetic correlation with both litter size (.22) and ovulation rate (.20) and a low residual correlation with both litter size (.03) and ovulation rate (.09). The genetic correlation between BW in rams and scrotal circumference was 0, whereas the residual correlation was .71. The genetic correlations of scrotal circumference with litter size and ovulation rate were -.25 and +.20, respectively.

Animals↗
PubMed1976

Genetic parameters of several measures of milk flow rate and milking time.

Heritabilities and genetic correlations of milking rate, time, and yield were estimated by intrasire regression of daughter on dam for 252 Holstein pairs. Heritabilities were: lactation yield, .51 +/- .11; peak rate, .47 +/- .11; bucket milk yield, .38 +/- .10; average rate, .37 +/- .12; milk yield to .45 kg/min, .19 +/- .12; total time, .17 +/- .12; duration of peak rate, .10 +/- .10; strip time, .08 +/- .15; yield during peak rate, .07 +/- .11; and strip yield, .01 +/- .17. The genetic correlation of peak rate with lactation milk yield was .69 +/- .08, indicating substantial genetic improvement in milking rate by selecting for milk production. The genetic correlation between total milking time and lactation milk yield was .50 +/- .20, indicating an increase in total milking time due to selection for milk. Direct selection for peak rate would provide an opportunity to reduce total milking time.

Animals↗
PubMed1977

Genetic parameters of serum cholesterol levels, activity and growth in mice.

Heritabilities (h2) of, and phenotypic and genetic correlations among, serum cholesterol (SC), levels of physical activity, growth, and body moisture content were estimated from data on 466 sire-son pairs of random-bred, ICR albino mice. Heritability estimates of SC and body moisture content were 0.31 +/- 0.07 and 0.29 +/- 0.11, respectively. Estimates of h2 for activity measured by standard exercise wheels at 28, 49 and 70 days of age were 0.31 +/- 0.17, 0.50 +/- 0.11 and 0.27 +/- 0.14 and for weight at 21, 44 and 67 days of age, were 0.11 +/- 0.09, 0.33 +/- 0.09 and 0.42 +/- 0.08, respectively. The estimates of h2 for weight gain ranged from 0.22 +/- 0.07 to 0.27 +/- 0.08. Significant negative phenotypic correlations occurred between activity and rate of body weight gain. A negative genetic correlation of -0.70 +/- 0.11 between SC and body moisture implied that SC and percent body fat are positively correlated. Genetic correlations among SC values and activity scores and between SC values and body weight gains were near zero.

Animals↗
PubMed1992

[Estimation of genetic parameters by using analysis of variance within unit].

In the estimation of heritability, various non-genetic factors must be excluded from the variance of sire or dam. The methods of sib correlation within unit, suggested by professor Sheng Zhilian is commonly used in China. This paper will provide evidence to verify this method theoretically and discuss the application of the method to systematic classification. In addition, in this paper the author suggest some other methods to estimate heritability by using analysis of variance within unit when the blood relationship exists between sire and dam. These methods not only make the estimation procedure of hertability simple but also have the same function of analyzing variance with multiple factors.

Analysis of Variance↗
PubMed1976

On estimating non-additive genetic parameters in chickens.

Several economically important traits in two Leghorn populations (over 9000 birds) were examined for additive and non-additive components of genetic variance and sex-linked effects. Data were analysed by two different statistical models based on least-squares procedures. 2. Six different covariances were first calculated between relatives; i.e., full-sibs 3/4-sisters, half-sisters, dam-daughters, grandam-granddaughters and aunt-nieces. 3. From the covariances, weighted least-squares equations were used to obtain estimates of variance components for additive genetic, dominance, maternal and sex-linkage effects. 4. The estimates of non-additive components were highly variable but generally small compared with the additive genetic estimates. 5. In general this study suggests that for most traits, with the possible exception of rate of egg production, there is relatively little non-additive genetic variation. 6. The consequences of possible negative correlations between additive effects and maternal effects are considered as they might apply to egg production in poultry.

Animals↗
PubMed1976

Genetic parameters of organ and body weights in the Japanese quail.

Heritability values were estimated for the weights of various internal organs and correlations among the organ weights were calculated using 279 male and 305 female birds of Japanese quail. The organs measured were heart, lungs, liver, gizzard, intestines, pancreas, spleen, kidneys, gonads, oviduct, muscles, and bones; total body weight was also recorded. The heritabilities for these internal organs ranged from 78 percent for bones to 17 percent for intestines, and showed no marked differences between male and female groups. In total body and muscle weight, however, males had higher heritabilities than females; male birds had larger genetic variances of these traits than females. Total body weight and muscle weight were stronly correlated both phenotypically and genetically. Correlations among other organs were generally low.

Animals↗
PubMed1975

Genetic parameters of dermal patterns of ridge counts.

Dermatoglyphic traits including ridge counts and pattern type counts on fingers were studied in 711 families representing six racial groups in Hawaii. Heritability tesimates were derived from regressions of offspring on father, mother and mid-parent values as well as from full-sib correlations. These estimates varied from 0.23 for radial loops to 0.80 for total ridge count. The heritability estimates were lower for ridge counts of single hands or single digits.

Dermatoglyphics↗
PubMed1976

[Dynamics of population genetics parameters and their statistical during assessment selection for quantitative characters. I. An additive model. One character].

The selection for a single additively inherited quantitative character is studied using computer models of 3 types: 1) all the individuals had the same viability, and the paratypic deviation does not depend on their genotype; 2) differential viability of genotypes is taken into account with respect to a number of heterozygous loci; 3) differential paratypic deviation is estimated, it is introduced like viability in the model 2. Two types of trancation selection, stabilizing and directed, under the selection coefficient of approximately 0.5 are studied. There are studied dynamics of genotypic (omega2gamma) and phenotypic (omega2phi) variances, the heritability index and it estimates (for the correlation progeny-parent--rho; for the regression progeny-parent--b; for half-sibses--v), and the non-equilibrium of a population for the models. The number of generation was 10; the population number in every generation was 200; the number of loci in the main experiment was 10.h2 values were calculated in the progeny before selection (p1, b1, v1) and after selection (p2, b2, v2). It is shown that stabilizing selection results in the formation of balanced gene complexes; the rate of decreasing omega2phi depends on the genetic length of a chromosome region in which genes, determining the character, are located, and not on the number of genes. The distribution of a character under directed selection depends on the type of the model. p2, b2, and v2 values are the worst. The best is the b1 value. It is concluded that the problem of predicting the selection effect using statistical estimates of heretability is connected with the problem of investigation of population heterogeneity and integrating their genetical structure.

Computers↗