Maximum Heritability Research Articles

Partitioning variances of growth in ultrasound longissimus muscle area measures in Angus bulls and heifers.

The objective of the study was to estimate variance components, heritability, and repeatability of ultrasound longissimus muscle area (ULMA) measures. Data included 4,653 serial ULMA measures from 882 purebred Angus bulls and heifers. Animals were born over a 4-yr period from 1998 to 2001. Each year, bulls and heifers were ultrasonically scanned four to eight times, with a 4- to 6-wk interval between scans. Initially, data were subdivided by scan session across years and were analyzed in a multitrait model (MTM). Data pooled across years and scan session were then analyzed using random regression models (RRM) to estimate trends in genetic parameter estimates. Additive direct genetic variance increased with advancing scan session ranging from 8.67 cm4 at the first scan (mean age = 35 wk) to a maximum of 19.48 cm4 at the sixth scan (mean age = 56 wk). Heritability of ULMA increased from 0.35 at first scan to a maximum of 0.48 at the fourth scan (mean age = 50 wk). Additive direct genetic variance and heritability values at about 1 yr of age (fifth scan) were 18.24 cm4 and 0.45, respectively. Estimates from RRM also showed an increase in sigma(a)2 and h2 with age. Trends in sigma(pe)2 estimates, although tending to fluctuate, also increased with age. Additive direct genetic variance at 1 yr of age ranged from 15.8 cm4 to 17.0 cm4 for the different models. Heritability of yearling ULMA measures ranged from 0.40 to 0.42 and repeatabilities ranged from 0.80 to 0.84. For the range of ages used in the current study, both MTM and RRM showed close to maximum heritability values at around 1 yr of age. Therefore, phenotypic differences in yearling ULMA between Angus cattle are better indicators of genetic differences than earlier measurements. Angus breeders could, therefore, use ULMA measures made at around 1 yr of age to select next generation parents.

Familial and genetic effects on motor coordination, laterality, and reading-related cognition.

Recent research has provided evidence for a genetically mediated association between language or reading-related cognitive deficits and impaired motor coordination. Other studies have identified relationships between lateralization of hand skill and cognitive abilities. With a large sample, the authors aimed to investigate genetic relationships between measures of reading-related cognition, hand motor skill, and hand skill lateralization. The authors applied univariate and bivariate correlation and familiality analyses to a range of measures. They also performed genomewide linkage analysis of hand motor skill in a subgroup of 195 sibling pairs. Hand motor skill was significantly familial (maximum heritability=41%), as were reading-related measures. Hand motor skill was weakly but significantly correlated with reading-related measures, such as nonword reading and irregular word reading. However, these correlations were not significantly familial in nature, and the authors did not observe linkage of hand motor skill to any chromosomal regions implicated in susceptibility to dyslexia. Lateralization of hand skill was not correlated with reading or cognitive ability. The authors confirmed a relationship between lower motor ability and poor reading performance. However, the genetic effects on motor skill and reading ability appeared to be largely or wholly distinct, suggesting that the correlation between these traits may have arisen from environmental influences. Finally, the authors found no evidence that reading disability and/or low general cognitive ability were associated with ambidexterity.

Genetic association between feed intake and feed intake behaviour at different stages of growth of group-housed boars

Abstract Voluntary feed intake, feed intake pattern and performance traits were recorded on 3188 group housed boars of Landrace and Large White tested from day 100 to day 170. Measurements of feed intake and feed intake behaviour were obtained by electronic feed dispensers (ACEMO) under ad libitum conditions. Heritabilities of feed intake in periods 1 to 5 and over the entire test period were estimated to be 0.16, 0.24, 0.30, 0.27, 0.26, and 0.22, respectively. The maximum heritability of daily feed intake in the third time period on test corresponds to about 130 days of age at about 85 kg of weight. Daily feed intake in this period showed a high genetic correlation with the average feed intake over the whole performance test (rg = 0.91). Estimates of genetic correlations between daily feed intake and feed conversion ratio, residual feed intake, average daily gain or backfat thickness were 0.04, 0.97, 0.62 and 0.42, respectively. Boars feed intake activities decreased over time while time per day in the feeder was almost constant. Traits of feed intake behaviour as feeding rate, feed intake/visit, number of visits, time per visit, and time per day in the feeder showed high heritabilities of 0.44, 0.51, 0.43, 0.42, and 0.43, respectively, but genetic correlations with performance and carcass traits were generally low. One exception was the behavioural trait time per day in the feeder with its moderate genetic correlations to daily feed intake (rg = 0.44) and average daily gain on test (rg = 0.32). Selection for lean growth will improve lean growth feed efficiency as indicated by the negative correlation of −0.47. But more efficient may be the use of the component traits, lean content, daily feed intake and daily gain in particular of the most informative test period.

Maximizing heritability of a linear combination of traits.

In 1971 Jones proposed an approximate procedure for finding that linear combination of scores which has maximum heritability in a twin sample. I give an exact small-sample procedure. I point out two problems: such procedures can over-optimize the heritability by capitalizing on chance, and confidence intervals and significance tests are needed. I give an approach using James-Stein shrinkage estimation and bootstrapped standard errors to address these problems. It appears that confidence intervals may be quite broad. To reduce the width of the confidence intervals, one can accept some small-sample bias in exchange for smaller sampling errors. The James-Stein approach to estimating coefficients is used to achieve reduced confidence interval width. I illustrate with a computational example using personality data.

Minimal genetic influences on plasma fibrinogen level in adult males in the NHLBI twin study

Plasma fibrinogen was determined in 189 twins participating at the Indiana center during the third examination of the NHLBI twin study with a mean age of 63 years. Moderate heritability estimates were obtained from 44 complete MZ pairs and 39 complete DZ pairs. After adjustment of fibrinogen levels for age and other confounding variables related to cardiovascular disease risk, the maximum likelihood heritability estimate was only 30% (p = 0.03). Plasma fibrinogen was most strongly associated with smoking and the presence of diabetes. Omitting all subjects with diabetes or cardiovascular disease further reduced the heritability estimates slightly, and most path models including genetic parameters provided no significant improvement in fit over a model determined solely by random environmental effects. Our results are consistent with the environment rather than genetic influences having a greater influence on the level of plasma fibrinogen.

GENETIC PARAMETERS AND INTER-RELATIONSHIP ANALYSIS IN LUCERNE (MEDICAGO SATIVA L.)

The genetic variability and correlations were worked out in forty two F progenies of the diallel crosses of seven parental varieites of lucerne for four characters. Analysis of variance revealed highly significant differences for all the characters. Seed yield expressed a maximum genotypic coefficient of variability and genetic advance as per cent of means with low heritability values, whereas plant height recorded the maximum heritability value. Green fodder yield was significantly and positively correlated with seed yield, branch number and plant height.

Quantitative genetic studies in flue-cured tobacco (Nicotiana tabacum L.). II. Certain physical and chemical characters

Genetic analyses of flue-cured tobacco leaf physical characteristics (percent lamina, lamina weight, and filling value) and chemical characteristics (percent total alkaloids, reducing sugars, nitrogen, ash, and cellulose) were conducted on a five parent diallel set (excluding reciprocals) evaluated at the Delhi Research Station in a randomized block design over a 2-year period. The ANOVA indicated that there was variance associated with the genetic source for all characteristics except filling value. Griffing's analysis for variances owing to general and specific combining abilities suggested additive genetic variance as the main source of genetic variation. Variances owing to specific combining ability for all traits were exceeded by the variance of the estimates indicating dominance to be of no major consequence in the expression of these physical and chemical traits. Total alkaloids and percent nitrogen expressed maximum heritability, and Wr–Vr graphs supported the conclusions. Parental diversity was evident from the scatter of array points and graphic analysis also indicated lack of dominance. Examination of pleiotropic effects revealed that traits related positively with alkaloids and nitrogen were negatively correlated with carbohydrate fractions such as reducing sugars and cellulose.Key words: tobacco, heritability, dominance, additive effects.

Genetic and Phenotypic Relations of Milk Production and Postpartum Length with Health and Lactation Curve Traits by Lactation

Milk, including its components, is the most important trait for dairy cattle. The relationship of 26 other traits with milk production was quantified both genetically and phenotypically to investigate any unfavorable responses associated with increased production. Traits with antagonistic positive correlations with 305-day mature-equivalent milk production included postpartum length, locomotive cost, and days dry. Postpartum length was calving interval or days in last lactation for terminal records. Traits with favorable negative correlations with milk production included culling rate, rate of decline in milk production per week, and mammary cost. Culling rate was a binomial variable defining whether a cow was eliminated from the herd during her lactation. Heritability of mature-equivalent milk production declined as lactation number increased: .27±.02 in first, .21±.02 in second, .16±.02 in third, and .15±.02 in fourth lactation. The maximum heritability of postpartum length was .06±.01 in the first lactation. Heritabilities of culling rate and days dry were less than .05. More than 62,000 records of progeny of 323 sires were analyzed.

Inheritance of Fruit Size in the Cultivated Tetraploid Blackberry [Rubus (Tourn.) L. subgenus Eubatus

Abstract Twelve seedling populations involving large, intermediate, and small-fruited parental clones of tetraploid blackberries were evaluated for fruit size inheritance. The amount and type of variation and the significant deviations from the mid-parent means in seedling distributions indicated that inheritance was quantitative with partial dominance for small fruit size. Maximum heritability, estimated by the genetic variance/phenotypic variance, was 0.76. Narrowsense heritability, estimated by regressing progeny on the mid-parents, was 0.62, indicating that most of the genetic variability (82%) was transmittable through the sexual cycle (gametes). These results suggest that simple breeding procedures based on inter-mating parent clones selected on the basis of their phenotypic performance are likely to produce significant genetic gains in fruit size of blackberries.

Inheritance of Fruit Size, Soluble Solids, and Ripening Date in Prunus domestica cv. Agen1

Abstract Genetic and environmental components of variance were estimated in 2 seedling populations of plum and prune at the University of California, Davis, California; the first population comprised 90 progeny of 14 open-pollinated parents, the second, 430 progeny of 50 controlled crosses among 28 parents. The estimates of phenotypic and genotypic variability associated with these traits in these 2 populations were nearly identical. Heritabilities, estimated by regressing the 500 progeny from the second population on their 50 mid-parents, were very high (0.80–1.0) for fruit size measurements and ripening dates, but zero for fruit yield. Also high (0.49) was the maximum heritability of percent soluble solids, estimated by the genetic variance/phenotypic variance. Phenotypic correlations among the traits fruit size, ripening date, and percent soluble solids are also small but significant in this seedling population. These results indicated that the rates of gain to be expected from mass selection on such populations are substantial.

Choosing between darkness and light: The ecological genetics of photic behaviour in the planktonic larva of Spirorbis borealis

The light-dark preference of individual Spirorbis borealis larvae was measured by the relative amount of time spent in the lighted half of a container. Specimens taken from a tidal pool were 20% more photonegative than those obtained outside the pool, probably because of natural selection against being washed out of the pool at high tide. The between-population behavioural difference was maintained in the laboratory, and is genetic in origin. Applying biometrical genetic analysis to larvae grouped into half-sib families, the within-population variation was used to estimate an upper limit to the heritability of 0.36. It is concluded that the differences among populations greatly exceed heritable variation within populations. A numerical selection model based on the estimated maximum heritability suggests, however, that the populations could diverge by 20% in less than a year, in response to local differences in the selection regime.

Yield performance with heritability measurements of half sib families obtained from maize variety Azam

This study evaluated the performance of 64 half sib families (HSF) derived from “Azam” variety of maize using partially balanced lattice square design with two replications. Data were recorded on grain yield and other agronomic traits. Observations showed difference in half-sib families for studied traits. Among the 64 half-sib families, minimum days to 50% tasseling (51 days) were observed for HS-49 while maximum (57 days) for HS-63. Minimum days to 50% silking (56 days) were counted for HS-6 while maximum (63 days) for HS-23. Minimum days to 50% anthesis (55 days) were counted for HS-1 and HS-6 while maximum (62 days) for HS-23. Similarly, minimum ASI (-2 days) were observed in HS-1, HS-15, HS-16, HS-28 and HS-63 while maximum (2 days) in HS-48. Minimum (60 cm) ear height was recorded for HS-11 and maximum (93.5 cm) for HS-28. Minimum fresh ear weight (1.3 kg) was weighted for HS-17 while maximum (3.2 kg) for HS-21. Grain moisture was recorded minimum (19.35 %) for HS-19 and maximum (31.25%) for HS-2. HS-42 showed minimum (28 g) 100 kernel weight while HS-5 showed maximum (47 g). Grain yield was minimum (2323 kg ha-1) for HS-17 and maximum (5742 kg ha-1) for HS-21. Maximum heritability estimate (0.92) was recorded for fresh ear weight, while minimum (0.41) was observed for ear height.