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PubMed1997

Feather pecking behaviour in White Leghorns, a genetic study.

1. Genetic variables of feather pecking (FP) behaviour in a 1993 commercial pure line of White Leghorns were estimated at the age of 6, 38 and 69 weeks. 2. Heritability estimates of performing FP were 0.05 +/- 0.06, 0.14* +/- 0.07 and 0.38** +/- 0.12 for 6, 38 and 69 weeks respectively for sum of pecks (PECKS) and 0.13* +/- 0.07, 0.13* +/- 0.07 and 0.35** +/- 0.12 for sum of bouts (BOUTS). 3. Heritability estimates of receiving FP were not significantly different from 0 except at 6 weeks (0.15* +/- 0.07 and the average of the 3 age classes (AVG) (0.22** +/- 0.09) for PECKS and at 6 weeks (0.15* +/- 0.07) using BOUTS. 4. Genetic correlations of performing FP among age classes were in general high and significant. This was not the case with receiving FP. 5. Plumage cover at 51 weeks had a negative genetic correlation with performing FP at 69 weeks and AVG, but not with receiving FP. No phenotypic correlations were significant between plumage and FP. 6. Body weight at 51 weeks had a negative genetic correlation with performing FP at AVG. 7. Heritability estimates for performing and receiving FP at 6 weeks correspond to those in the literature. No estimates have previously been reported on feather pecking at 38 weeks or 69 weeks. 8. Selection of birds with no or a very low tendency to perform feather pecking should, on the basis of our results, be feasible.

Aggression↗

PubMed2003

Genetics of fibrin clot structure: a twin study.

Coronary artery thrombosis following plaque rupture is an important feature of myocardial infarction, and studies have highlighted the role of coagulation in this condition. Although genetic and environmental influences on the variance in coagulation protein concentrations have been reported, there are no data on the heritability of structure/function of the final phenotype of the coagulation cascade, the fibrin clot. To assess genetic and environmental contributions to fibrin structure, permeation and turbidity studies were performed in 137 twin pairs (66 monozygotic, 71 dizygotic). The environmental influence (e2) on pore size (Ks) (e2 = 0.61 [95% confidence interval (CI), 0.45-0.80]) and fiber size (e2 = 0.54 [95% CI, 0.39-0.73]) was greater than the heritability (h2 = 0.39 [95% CI, 0.20-0.55] and 0.46 [95% CI, 0.27-0.62], respectively). After correction for fibrinogen levels, the environmental effect persisted for Ks (e2 = 0.61), but genetic influence assumed a greater importance in determining fiber size (h2 = 0.73). Multivariate analysis revealed an overlap in the influence of genetic and environmental factors on fibrinogen levels, Ks, and fiber size. Factor XIII B subunit showed environmental and genetic correlation with fibrinogen and fiber size and a genetic correlation with Ks. The results indicate that genetic and environmental influences are important in determining fibrin clot structure/function.

Adolescent↗

PubMed2006

[Correlation of genetic instability of nm23H1 gene to clinicopathologic features of epithelial ovarian carcinoma].

BACKGROUND & OBJECTIVE: Genetic instability, including microsatellite instability (MSI) and loss of heterozygosity (LOH), is the main reason for anti-oncogenes function maladjustment, and tumorigenesis. This research was to explore the correlation of genetic instability of nm23H1 gene to clinicopathologic features of epithelial ovarian carcinoma, and provide experimental basis for revealing the mechanism of nm23H1 gene function and tumor metastasis. METHODS: MSI and LOH of locus D17S396 in 25 specimens of epithelial ovarian carcinoma and relevant pericancerous tissues were detected by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) with ordinary silver staining. EnVision immuno-histochemistry and Leica-Qwin computer imaging techniques were used to assess the expression of nm23H1 protein. RESULTS: The detection rates of MSI and LOH of locus D17S396 in the 25 specimens of epithelial ovarian carcinoma were 16.00% and 24.00%, and the positive rate of nm23H1 protein was 56.00%. The frequency of LOH was significantly higher in the cases with lymph node metastasis than in those without metastasis (66.67% vs. 10.53%, P<0.01), and was significantly higher in the cases at FIGO stage III-IV than in those at stage I-II (50.00% vs. 11.76%, P<0.05). The positive rate of nm23H1 protein was significantly lower in the cases with lymph node metastasis than in those without lymph node metastasis (16.67% vs. 68.42%, P<0.05), and was significantly lower in the cases at FIGO stage III-IV than in those at stage I-II (25.00% vs. 70.59%, P<0.05). The expression intensity of nm23H1 protein had no correlation to clinicopathologic factors of epithelial ovarian carcinoma when analyzed by computer imaging techniques. The positive rate of nm23H1 protein was significantly lower in the cases with LOH of locus D17S396 than in those without LOH of locus D17S396 (0.00% vs. 73.68%, P<0.01). CONCLUSIONS: The occurrence of LOH may be a molecular marker for the canceration of ovarian tissues. MSI and LOH of nm23H1 gene regulate the development of epithelial ovarian tumor through different pathways. LOH could inhibit the expression of nm23H1 in epithelial ovarian carcinoma.

Cystadenocarcinoma, Mucinous↗

PubMed1989

Relationship of bull fertility with daughter fertility and production traits in Holstein dairy cattle.

The phenotypic and genetic correlations between fertility ratings of AI bulls for conception rate and their estimated breeding values for daughters' fertility and production traits were calculated. Genetic correlations between fertility ratings of bulls for conception and heifer fertility traits (age at first breeding, age at last breeding, and number of insemination per conception) were negative and ranged from -.04 to -.23, indicating daughters of bulls with high fertility ratings were younger at first breeding and required fewer services to conceive. In general, genetic correlations between fertility ratings of bulls for conception rate and cow fertility traits (days from calving to first breeding, days open, and number of inseminations per conception) and production traits (breed class average milk and fat and fat percentage) in the first two lactations were also moderate to high and in the favorable direction. Although heritability of both male and female fertility is low, these data indicate that heavy use of sires with high fertility ratings could have a mild positive effect on both male and female fertility. Evidence is also found to indicate that in this breed, selection for increased milk yield should not impair genetic ability of cows to reproduce.

Animals↗

PubMed1992

[The genetic analysis of long-term index selection--a simulation experiment].

The genetic effects of long-term index selection were investigated by means of Monte Carlo Method. The response and the effect on genetic structure of population to selection using four methods, that is theoretical index, emperical index, restricted index and single-trait selection, were compared. Results obtained from 50 generations demonstrated that much greater response was achieved in large populations, and selection in small ones led to a decrease in selection limit. Genetic correlation played an important role on response in small populations. Emperical index selection was more effective than theoretical index, restricted index had less response in the early period of selection but greater response in later period and also had less effect on genetic structure of population even if the genetic correlation was intense. Meanwhile, index selection could cause decrease in additive genetic variance and beritabilities while genetic correlation changed depending on the coefficients of index formulae. The suggestion is that emperical index or restricted index should be used for long-term selection for multi-traits.

Computer Simulation↗

PubMed1991

Estimates of covariances between reproduction and growth in Australian beef cattle.

Estimates of covariance components between scrotal circumference, serving capacity, days to calving, and yearling and final weight were obtained for Hereford, Angus, and Zebu cross cattle in temperate and tropical Australia. Analyses were carried out by REML employing a derivative-free algorithm and fitting bivariate animal models. Aspects of modeling and computational requirements related to the use of this method are discussed. Estimates of heritabilities agreed closely with those from univariate analyses, being low for female reproductive performance and moderate to high for male reproduction and growth. Estimates of genetic correlation between male and female fertility traits were low but favorable, being -.25, -.28, and -.41 between scrotal circumference and days to calving for Herefords, Angus, and Zebu crosses, respectively. Genetic correlations between male reproductive traits and weights ranged from .24 to .52 for the temperate breeds and were higher (.65 to .69) for Zebu crosses. Phenotypic correlations between scrotal circumference and weights were similar for all breeds, ranging from .32 to .47, whereas serving capacity and weights were phenotypically unrelated. Estimates of correlations between days to calving and weights were less consistent. Phenotypically, there was little association between the two traits. Genetic correlations for Zebu crosses were negative and low to moderate (-.36 to -.66) and estimates for Angus were close to zero.

Analysis of Variance↗

PubMed1994

Genetic and phenotypic parameter estimates of pelvic measurements and birth weight in beef heifers.

Data on 1210 spring-born (1983 to 1988) yearling heifers were analyzed by paternal half-sib procedures to obtain genetic and phenotypic parameter estimates involving birth weight and pelvic measurements. Data included records on 629 Angus, 325 Simmental, and 256 Salers representing 93, 49, and 22 paternal half-sib sire groups, respectively. Heritabilities for birth weight (BW), pelvic height (PH), pelvic width (PW), and pelvic area (PA) for Angus were 0.30, 0.61, 0.28, and 0.43, respectively. Corresponding values for Simmental and Salers heifers were 0.14, 0.34, 0.44, 0.37, and 0.18, 0.02, 0.29, 0.15, respectively. Genetic correlations among pelvic measurements (PH-PW, PH-PA, PW-PA) were positive (0.25 to 1.03) except for the estimate of -0.07 for PH-PW in Simmentals. Genetic correlations between BW and the 3 pelvic measurements (BW-PH, BW-PW, BW-PA) were negative (-0.18 to -0.36) except for the estimates of 0.53 (BW-PW) and 0.26 (BW-PA) in Simmentals and 2.84 (BW-PH) and 0.39 (BW-PA) in Salers. Phenotypic correlations among pelvic measurements ranged from 0.16 to 0.80. Phenotypic correlations between birth weight and the 3 pelvic measurements were consistently lower (-0.02 to 0.09) than the genetic correlations.

Journal Article↗

PubMed2004

Genetic components of days open under heat stress.

A reaction norm approach was used to estimate the genetic parameters of days open (DO) with a model that accounted for heat stress. Data included DO records for Georgia, Tennessee, and North Carolina in the Southeastern United States. A fixed effect model included herd-year, month of calving (MOC), age of cow, and a regression on 305-d milk yield. The reaction norm model additionally included the effect of animal with random regression on a heat stress index (HI), calculated as the standardized solutions to MOC derived from the fixed effect model; the residual variance was assumed to be a function of the HI. The shape of the distribution of the HI was close to a sinusoidal function with the highest value in March/April and the lowest value in September. Genetic and residual variances and heritabilities were highest for spring calvings and lowest for fall calvings. The variance associated with the random regression of the highest level of HI was 33% of the genetic variance of the regular animal genetic effect. Genetic correlation between these effects was 0.67. As a validation, DO data were grouped into 4 seasons of calving and treated as different traits. A 4-trait mixed linear model that included the fixed effects listed above except MOC, was used to analyze the grouped data. In general, the estimates of genetic and residual variances of the multiple trait analyses followed those of the reaction norm model. Genetic correlations of spring with summer, and fall with winter were both 0.90. Genetic correlations between spring/summer and fall/winter were around 0.80. The reaction norm model for DO allows inexpensive genetic evaluation of fertility under heat stress. Results of such an evaluation may strongly depend on editing criteria and model specifications.

Analysis of Variance↗

PubMed2003

Estimates of heritability for ossification of the cartilages of the front feet in the Finnhorse.

REASONS FOR PERFORMING STUDY: Ossification of the cartilages in the foot is common in coldblooded horses, but prevalence as well as ossification pattern varies between breeds; research on estimation of heritability for the condition has been limited. OBJECTIVES: Our purpose was to calculate estimates of 1) heritability for ossification parameters of the cartilages in the front feet of the Finnhorse and 2) genetic correlations between the different ossification parameters. METHODS: Estimates of heritability for different ossification parameters of the cartilages in the front feet and of genetic correlations between different parameters were evaluated in data consisting of dorsopalmar radiographs of the front feet and pedigree up to the fourth generation of 964 Finnhorses (age > or = 2 years; 345 females and 619 males). Ossification at the base of the cartilages and total ossification, including separate centres of ossification, were graded 0-5 according to the most proximal point of ossification and the presence of separate centres of ossification was recorded separately. The data were analysed using a model including a fixed sex-age subclass effect and a random animal effect. Variance and covariance components were estimated with the restricted maximum likelihood (REML) method assuming an animal model. RESULTS: Females had more ossification than males and this difference increased with age. The ossification in the medial cartilages progressed significantly with age in females but not in males. In the lateral cartilages, the increase in ossification with age was evident in both sexes. Separate centres of ossification were an incidental finding. Estimates of heritability for the ossification parameters varied slightly between the cartilages as well as between the front feet. For total ossification, the estimates of heritability varied between 0.31 (right lateral) and 0.50 (left medial) and were slightly higher for ossification at the base of the cartilages. High genetic correlations were found for total ossification between the medial and lateral cartilages in the foot and for parallel ossification parameters between the right and left foot. CONCLUSIONS: The estimates of heritability were relatively high, and both cartilages and front feet have a similar genetic tendency to ossify. POTENTIAL RELEVANCE: This information is useful in further studies assessing other factors contributing to the ossification process and also in the planning and modifying breeding programmes.

Aging↗

PubMed1999

Artificial selection for increased wheel-running activity in house mice results in decreased body mass at maturity.

To test the hypothesis that body size and activity levels are negatively genetically correlated, we conducted an artificial selection experiment for increased voluntary wheel-running activity in house mice (Mus domesticus). Here, we compare body masses of mice from control and selected lines after 14 generations of selection. In both groups, beginning at weaning and then for 8 weeks, we housed half of the individuals with access to running wheels that were free to rotate and the other half with wheels that were locked to prevent rotation. Mice from selected lines were more active than controls at weaning (21 days) and across the experiment (total revolutions during last week: females 2.5-fold higher, males 2.1-fold higher). At weaning, mice from selected and control lines did not differ significantly in body mass. At 79 days of age, mice from selected lines weighed 13.6 % less than mice from control lines, whereas mice with access to free wheels weighed 4.5 % less than 'sedentary' individuals; both effects were statistically significant and additive. Within the free-wheel-access group, individual variation in body mass of males was negatively correlated with amount of wheel-running during the last week (P<0.01); for females, the relationship was also negative but not statistically significant (P>0.40). The narrow-sense genetic correlation between wheel-running and body mass after 8 weeks of wheel access was estimated to be -0. 50. A negative genetic correlation could account for the negative relationship between voluntary wheel-running and body mass that has been reported across 13 species of muroid rodents.

Animals↗

PubMed1999

"Quasi-REML" correlation estimates between production and health traits in the presence of selection and confounding: a simulation study.

Performance of the "quasi-REML" method for estimating correlations between a continuous trait and a categorical trait, and between two categorical traits, was studied with Monte Carlo simulations. Three continuous, correlated traits were simulated for identical populations and three scenarios with either no selection, selection for one moderately heritable trait (Trait 1, h2 = .25), and selection for the same trait plus confounding between sires and management groups. The "true" environmental correlations between Traits 2 (h2 = .10) and 3 (h2 = .05) were always of the same absolute size (.20), but further data scenarios were generated by setting the sign of environmental correlation to either positive or negative. Observations for Traits 2 and 3 were then reassigned to binomial categories to simulate health or reproductive traits with incidences of 15 and 5%, respectively. Genetic correlations (r(g12), r(g13), and r(g23) and environmental correlations (r(e12), r(e13), and r(e23)) were estimated for the underlying continuous scale (REML) and the visible categorical scales ("quasi-REML") with linear multiple-trait sire and animal models. Contrary to theory, practically all "quasi-REML" genetic correlations were underestimated to some extent with the sire and animal models. Selection inflated this negative bias for sire model estimates, and the sign of r(e23) noticeably affected r(g23) estimates for the animal model, with greater bias and SD for estimates when the "true" r(e23) was positive. Transformed "quasi-REML" environmental correlations between a continuous and a categorical trait were estimated with good efficiency and little bias, and corresponding correlations between two categorical traits were systematically overestimated. Confounding between sires and contemporary groups negatively affected all correlation estimates on the underlying and the visible scales, especially for sire model "quasi-REML" estimates of genetic correlation. Selection, data structure, and the (co)variance structure influences how well correlations involving categorical traits are estimated with "quasi-REML" methods.

Animal Husbandry↗

PubMed1999

Sire marbling score expected progeny difference and weaning weight maternal expected progeny difference associations with age at first calving and calving interval in Angus beef cattle.

Field records from the American Angus Association were used to study the associations of sire marbling score EPD and sire weaning weight maternal (milk) EPD with age at first calving (AFC) and calving interval (CI). Cows were selected based on the accuracy of their sire's milk (> or =.7) or marbling (> or =.6) EPD. The data were screened using biological constraints, and regression models were used to identify records that were greater than 5 SD from the mean. The AFC was modeled for both milk and marbling data sets to account for effects of year, sire EPD, and their interaction. The CI was subdivided into first, second, and mature calving interval traits and modeled to account for state, year, calf sex, calf birth weight (BW), calf weaning weight (WW), sire EPD, and interactions of EPD with year and state. Derivative-free REML was used to estimate heritability and genetic correlations for AFC and CI. Sire milk EPD and marbling EPD were predictors of AFC (P < .001); however, pooled estimates were unreliable because of state x EPD interactions (P < .001). Increases in sire milk EPD resulted in reductions in AFC; however, there was no consistent pattern to effects of marbling EPD increases. Models accounted for < 8% of variation in AFC. Sire milk EPD was not a predictor of first, second, or mature CI (P > .1). Sire marbling score EPD was not a predictor of second, or mature CI (P > .1); however, it was associated (P = .059) with first CI, although regression estimates varied across states and prevented pooling. The BW, sex, and WW were predictors of CI (P < .001). Increases in BW resulted in longer mature CI, and mature CI decreased as WW increased. The AFC was heritable (.22), and CI traits had heritabilities ranging from .01 to .03. The AFC was genetically correlated with first CI (-.6) and mature CI (-.93). Genetic correlations between CI traits were uninterpretable because of low additive genetic variances. In conclusion, sire marbling score and milk EPD do not seem to be reliable predictors of AFC or CI. The BW and WW have significant but small effects on AFC and CI. Selection for AFC is possible, but earlier calving heifers may have longer calving intervals.

Adipose Tissue↗

PubMed2025

Polygenic and developmental profiles of autism differ by age at diagnosis.

Although autism has been historically conceptualised as a condition that emerges in early childhood, many autistic people are diagnosed later in life. It is unknown whether earlier and later diagnosed autism have different developmental trajectories and genetic profiles. Using longitudinal data from four independent birth cohorts, we demonstrate that two different socioemotional and behavioural trajectories are associated with age at diagnosis. In independent cohorts of autistic individuals, common genetic variants account for approximately 11% of the variance in age at autism diagnosis, comparable to the contribution of individual sociodemographic and clinical factors, which typically explain less than 15% of this variance. We further demonstrate that the polygenic architecture of autism can be decomposed into two modestly genetically correlated (rg = 0.38, SE = 0.07) autism polygenic factors. One of these factors is associated with earlier autism diagnosis, and lower social and communication abilities in early childhood but is only modestly genetically correlated with ADHD and mental health conditions. Conversely, the second factor is associated with later autism diagnosis, increased socioemotional and behavioural difficulties in adolescence, and has moderate to high positive genetic correlations with Attention-Deficit/Hyperactivity Disorder and mental health conditions. These findings indicate that earlier and later diagnosed autism have different developmental trajectories and genetic profiles. Our findings have important implications for how we conceptualise autism and provide one model to explain some of the diversity within autism.

Journal Article↗

PubMed2005

[Correlation of genetic polymorphisms in nucleotide excision repair system to sensitivity of advanced non-small cell lung cancer patients to platinum-based chemotherapy].

BACKGROUND & OBJECTIVE: DNA repair system plays an important role in tumor sensitivity to platinum-based chemotherapy. This study was to examine the correlations of polymorphisms in nucleotide excision repair system to sensitivity of advanced non-small cell lung cancer (NSCLC) to platinum-based chemotherapy. METHODS: Treatment outcomes of 200 advanced NSCLC patients, treated with platinum-based chemotherapy, were evaluated. XPC-PAT, XPD Lys751Gln (rs1052559), and ERCC1 C8092A (rs1052559) were genotyped by polymerase chain reaction-amplified fragment length polymorphism (PCR-AFLP) or PCR-restrictive fragment length polymorphism (PCR-RFLP) methods in the 200 patients. Unconditional logistic regression model was used to analyze the correlation of genetic polymorphisms to clinical response. RESULTS: The distributions of XPC-PAT genotypes differed significantly between response group (complete response + partial response) and un-response group (stable disease + progressive disease)(P=0.023). The XPC LL genotype carriers had higher response rate than the SS genotype carriers (OR=3.04; 95% CI=1.25-7.41, P= 0.015). The XPD Lys751Gln and ERCC1 C8092A polymorphisms were not found to be associated with platinum-based chemotherapy. However, these 3 genetic polymorphisms in nucleotide excision repair system had interaction in the drug sensitivity (P=0.021). CONCLUSION: The genetic polymorphisms of XPC-PAT, XPD Lys751Gln, and ERCC1 C8092A in nucleotide excision repair system may be associated with sensitivity of NSCLC patients to platinum-based chemotherapy.

Adult↗

PubMed2005

Effect of age and housing system on genetic parameters for broiler carcass traits.

The effect of age and housing system on genetic parameters for BW and carcass traits was investigated. Traits were measured on broilers of different ages (48, 63, and 70 d). Birds in the 48 and 70 d groups were raised in group housing, whereas birds in the 63 d group were raised in the same housing up to 22 d and in individual cages between 22 and 63 d. Each group consisted of approximately 2,000 individuals from a single group of parents. Carcass, breast meat, abdominal fat, and back half were expressed as percentage of BW. The heritabilities of BW at 48, 63, and 70 d were 0.31, 0.26, and 0.19, respectively, and the heritabilities of back half percentage at 48, 63, and 70 d were 0.42, 0.38, and 0.21, respectively. For other carcass traits, heritabilities were in the same range in different age groups. A positive genetic correlation was found between BW and valuable parts of carcass (breast meat and back half) at 48 d; these relationships were negative at 70 d. The genetic correlation between BW and abdominal fat percentage at 70 d was higher than at 48 d. The increase in growth at 48 d was accompanied by increase in valuable parts; at 70 d it was accompanied by an increase in abdominal fat percentage. The genetic correlation of BW at 48 d between individual cage and group housing demonstrated a genotype by environment interaction for performance of birds, which has consequences for design of breeding schemes.

Aging↗

PubMed2025

Polygenic and developmental profiles of autism differ by age at diagnosis.

Although autism has historically been conceptualized as a condition that emerges in early childhood1,2, many autistic people are diagnosed later in life3-5. It is unknown whether earlier- and later-diagnosed autism have different developmental trajectories and genetic profiles. Using longitudinal data from four independent birth cohorts, we demonstrate that two different socioemotional and behavioural trajectories are associated with age at diagnosis. In independent cohorts of autistic individuals, common genetic variants account for approximately 11% of the variance in age at autism diagnosis, similar to the contribution of individual sociodemographic and clinical factors, which typically explain less than 15% of this variance. We further demonstrate that the polygenic architecture of autism can be broken down into two modestly genetically correlated (rg = 0.38, s.e. = 0.07) autism polygenic factors. One of these factors is associated with earlier autism diagnosis and lower social and communication abilities in early childhood, but is only moderately genetically correlated with attention deficit-hyperactivity disorder (ADHD) and mental-health conditions. Conversely, the second factor is associated with later autism diagnosis and increased socioemotional and behavioural difficulties in adolescence, and has moderate to high positive genetic correlations with ADHD and mental-health conditions. These findings indicate that earlier- and later-diagnosed autism have different developmental trajectories and genetic profiles. Our findings have important implications for how we conceptualize autism and provide a model to explain some of the diversity found in autism.

Humans↗

PubMed2005

Genetics of efficient feed utilization and national cattle evaluation: a review.

Selection for the wide range of traits for which most beef breed associations calculate expected progeny differences focus on increasing the outputs of the production system, thereby increasing the genetic potential of cattle for reproductive rates, weights, growth rates, and end-product yield. Feed costs, however, represent a large proportion of the variable cost of beef production and genetic improvement programs for reducing input costs should include traits related to feed utilization. Feed conversion ratio, defined as feed inputs per unit output, is a traditional measure of efficiency that has significant phenotypic and genetic correlations with feed intake, growth rate, and mature size. One limitation is that favorable decreases in feed to gain either directly or due to correlated response to increasing growth rate do not necessarily relate to improvement in efficiency of feed utilization. Residual feed intake is defined as the difference between actual feed intake and that predicted on the basis of requirements for maintenance of body weight and production. Phenotypic independence of residual feed intake with growth rate, body weight, and other energy depots can be forced. However, genetic associations may remain when a phenotypic prediction approach is used. Heritability estimates for phenotypic residual feed intake have been moderate, ranging from 0.26 to 0.43. Genetic correlations of phenotypic residual feed intake with feed intake have been large and positive, suggesting that improvement would produce a correlated response of decreased feed intake. Residual feed intake estimated by genetic regression results in a zero genetic correlation with its predictors, which reduces concerns over long-term antagonistic responses such as increased mature size and maintenance requirements. The genetic regression approach requires knowledge of genetic covariances of feed intake with weight and production traits. Cost of individual feed intake measurements on potential replacements must be considered in implementation of national cattle evaluations for efficiency of feed utilization. These costs need to be compared to expected, and, if possible, realized rates of genetic change and the associated reduction in feed input requirements.

Animal Feed↗

PubMed2004

Constancy of the G matrix in ecological time.

The constancy of the genetic variance-covariance matrix (G matrix) across environments and populations has been discussed and tested empirically over the years but no consensus has so far been reached. In this paper, I present a model in which morphological traits develop hierarchically, and individuals differ in their resource allocation and acquisition patterns. If the variance in resource acquisition is many times larger than the variance in resource allocation then strong genetic correlations are expected, and with almost isometric relations among traits. As the variation in resource acquisition decreases below a certain threshold, the correlations decrease overall and the relations among traits become a function of the allocation patterns, and in particular reflecting the basal division of allocation. A strong bottleneck can break a pattern of strong genetic correlation, but this effect diminishes rapidly with increasing bottleneck size. This model helps to understand why some populations change their genetic correlations in different environments, whereas others do not, since the key factor is the relation between the variances in resource acquisition and allocation. If a change in environment does not lead to a change in this ratio, no change can be expected, whereas if the ratio is changed substantially then major changes can be expected. This model can also help to understand the constancy of morphological patterns within larger taxa as a function of constancy in resource acquisition patterns over time and environments. When this pattern breaks, for example on islands, larger changes can be expected.

Analysis of Variance↗