Responses of prolactin and hair growth to selection for age at puberty in Angus cattle

A trial was carried out over a 7-year period (1999 to 2005 calf crops) to compare indicators of seasonality in Angus cattle, which were part of a long-term genetic selection experiment. Divergent selection was applied for early ('AGE-') or late ('AGE+') age at puberty (AP) in heifers, and selection lines differed over the 7-year period by 62 days (15% of the mean). The primary measures of seasonality studied in 629 heifer progeny (59 sire groups) were serum concentration of prolactin (PRL), and winter and summer hair growth. Serial samples were obtained for PRL from 11 to 18 months of age, and data were analysed with adjustment for cortisol concentration. Using restricted maximum likelihood procedures with an animal model, heritability estimates were: AP, 0.26 ± 0.03; log(e)PRL concentration, 0.23 ± 0.07; log(e)cortisol concentration, 0.22 ± 0.07; hair weight, 0.21 ± 0.04; and hair length, 0.09 ± 0.05. Corresponding repeatability estimates for the last four traits were 0.49 ± 0.03, 0.38 ± 0.03, 0.21 ± 0.04, and 0.64 ± 0.02, respectively. The genetic correlation between AP and log(e)PRL concentration was estimated at -0.29 ± 0.13 (P < 0.05). PRL concentration in the AGE- line after passing through puberty was 11 ± 5% lower than in the AGE+ line (P < 0.05). Line effects were not significant for hair weight or hair length. It was concluded that divergent selection for AP changed PRL concentration, which may partly reflect sensitivity to changing day length.     

Estimation of heritability and repeatability of resting metabolic rate in birds, with free-living pied flycatchers Ficedula hypoleuca (Aves: Passeriformes) as an example

Estimates of a trait heritability and repeatability can get at an idea of its usefulness for being an individual characteristic and its ability to change under selection pressure. Heritability and repeatability of energetic parameters still poorly studied in birds. The most important physiological characteristic of homoiotherms is resting metabolic rate (RMR), which, in the absence of productive processes, does not exceed basal metabolic rate (BMR). We estimated BMR repeatability in free-living pied flycatchers in Moscow Region (55 degrees 44' N, 36 degrees 51' E; 1992-2008) and Tomsk (56 degrees 20' N, 84 degrees 56' E; 2008-2009) populations over intervals from 40 days to 3 years. In Moscow Region population, BMR repeatability amounted to tau = 0.34 +/- 0.10 (n=80) if measured over 1 year interval, tau = 0.60 +/- 0.15 (n=19) if measured over 2 years interval, and tau = 0.85 +/- 0.13 (n=6) if measured over 3 years interval providing that consecutive BMR measurements were done in the same period of reproductive season. In Tomsk population, BMR repeatability, measured over 1 year interval, amounted to tau = 0.49 +/- 0.11 (n=50). Repeatability is a measure of a trait constancy and sets the upper limit of its heritability. To estimate RMR heritability, cross-fostering experiments have been conducted in 2003-2005 with flycatchers of Moscow Region population. RMR of chicks positively correlated with BMR of their biological fathers, whereas such correlation in metabolic rates between chicks and their foster fathers was absent. The RMR heritability estimate turned out to be h2 = 0.43 +/- 0.17 (n=210). The obtained estimates of heritability and repeatability of fundamental energetic traits are rather high for physiological features. This suggests the existence of a potential for direct selection on BMR and evolutionary stable diversity of avian populations with regard to basal metabolic rate.     

Phenotypic and genetic parameters compared during repeated measures of longissimus muscle area and subcutaneous fat thickness in Nelore cattle

Real-time ultrasound is currently used for in vivo carcass evaluation of beef cattle. We estimated heritability and repeatability coefficients for ultrasound-measured carcass traits in Nelore cattle. We measured longissimus muscle area, backfat thickness, and rump fat thickness in male and female animals ranging in age from 10 to 26 months. The variance components were estimated by single-trait analysis using the derivative-free restricted maximum likelihood method, under an animal model. The complete data file included 3077 records of 1172 animals born between 2003 and 2008. Two analyses were performed using a repeatability model: a) all records of longissimus muscle area, backfat thickness, and rump fat thickness of animals aged 10 to 26 months, and b) considering two age periods (11 to 17 and 18 to 24 months). The heritability estimates ranged from 0.33 to 0.46 for longissimus muscle area, from 0.20 to 0.26 for backfat, and from 0.26 to 0.29 for rump fat, demonstrating that direct selection for these traits can provide genetic gain. The repeatability estimates were moderate, ranging from 0.42 to 0.73. The highest repeatability estimates were obtained for longissimus muscle area in both the first (0.70) and second (0.73) analyses. The repeatability estimates suggest that ultrasound measures are precise; higher precision was obtained for longissimus muscle area than for subcutaneous fat thickness. The latter could be obtained during periods of greater feed availability to increase precision.     

Heritability of ram mating success in multi-sire breeding situations

Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for log_e(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (log_e(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain.     

Genetic analysis of ewe productivity traits in Moghani sheep

Genetic and environmental (co)variance components for productivity traits in Moghani sheep were estimated using data from 1344 ewes. The data were collected in the Jafarabad breeding station, north-east of Iran, during a 13-year period (1995-2008). The studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). A model including direct additive genetic effects as well as permanent environmental effects related to repeated records of ewe was the most appropriate model for all the studied traits. Genetic parameters were estimated applying restricted maximum likelihood (REML) procedure. Direct heritability estimate for LSB, LSW, LMWLB, LMWLW, TLWB and TLWW were 0.11, 0.02, 0.15, 0.07, 0.07 and 0.06, respectively. Corresponding values for repeatability estimates were 0.16, 0.19, 0.18, 0.11, 0.13 and 0.09. Genetic correlations between the studied traits ranged from −0.99 for LSB-LMWLB and LSW-LMWLB to 0.99 for LSB-TLWB. Phenotypic and environmental correlation estimates were generally lower than those of genetic ones. Estimates of permanent environmental correlation among traits were positive and medium to high. Although low direct heritabilities were estimated for the reproductive traits, as these traits are of interest then they should be included in a breeding program.     

Age-stratified heritability estimation in the Framingham Heart Study families

The Framingham Heart Study provides a unique source of longitudinal family data related to CVD risk factors. Age-stratified heritability estimates were obtained over three age groups (31-49 years, 50-60 years, and 61-79 years), reflecting the longitudinal nature of the data, for four quantitative traits. Age-adjusted heritability estimates were obtained at a single common time point for the same four quantitative traits. The importance of these groups is that they consist of the same individuals. The highest age-stratified heritability estimate (h2 = 0.88 (+/- 0.06)) was for height in the model adjusting for gender over all three age groups. SBP gave the lowest heritability estimate (h2 = 0.15 (+/- 0.11)) for the 70 age group in the model adjusting for gender, height, BMI, smoker, and drinker. BMI had slightly higher estimates (h2 = 0.64 (+/- 0.11)) in the 40 age group than previously published. The highest age-adjusted heritability estimate (h2 = 0.90 (+/- 0.06)) was for height in the model adjusting for gender. SBP gave the lowest heritability estimate (h2 = 0.38 (+/- 0.09)) for unadjusted model. These results indicate that some common, complex traits may vary little in their genetic architecture over time and suggest that a common set of genes may be contributing to observed variation for these longitudinally collected phenotypes.     

Development of a selection index to improve market value of cultured Atlantic salmon (Salmo salar).

Genetic parameters were estimated on growth and development traits using analyses of variance and covariance of 42 full-sib families from a select line, 39 full-sib families from a control line of the same strain, and 37 full-sib families from another unselected strain. The traits included percent 1+ smolts, percent sexually immature fish after 1 year in seawater (nongrilse), and fork length measured at intervals throughout the production cycle. The number of fish sampled per family was 30 of 300-1500 for all freshwater traits and 15-60, i.e., all individuals present, for all seawater traits. Heritability estimates of freshwater traits had a broad range (0.15-0.61), but estimates were lower for seawater traits (0.06-0.29). There was a general reduction in heritability estimates for traits measured at increasing ages both in freshwater and seawater. These reductions may in part represent declines of maternal and common environmental effects that inflate heritability estimated from full-sib families. The genetic correlations indicated positive associations between freshwater and seawater growth parameters. However, the correlations decreased with increasing intervals between measurements. A selection index was developed using the estimates of the genetic and phenotypic parameters for three economically important traits: percent 1 + smolts, percent nongrilse, and harvest length. The seawater traits, percent nongrilse, and fork length at 17 months (harvest length) were the most important in the index.     

Genetic and phenotypic aspects of foot lesion scores in sheep of different breeds and ages

Footrot is a costly endemic disease of sheep. This study investigates the potential to decrease its prevalence through selective breeding for decreased lesion score. Pedigreed mule and Scottish Blackface (SBF) ewes were scored for lesions on each hoof on a 0 to 4 scale for up to 2 (SBF ewes) or 4 (mules) times over 2 years. One score was obtained for SBF lambs. An animal was deemed to have lesions (severe lesions) if at least one hoof had a score of at least 1 (2). The prevalence of lesions was 34% in lambs, 17% in SBF ewes and 51% in mules. The heritability of lesions (severe lesions) analysed as repeated measurements of the same trait in a threshold model was 0.19 (0.26) in SBF ewes and 0.12 (0.19) in mules. Estimates for the sum and maximum of scores as well as the number of feet affected were much lower, as were estimates for permanent animal effects (i.e. non-genetic effects associated with an animal). When successive scores on the same animal were analysed as correlated traits, heritability estimates for most traits tended to be higher, except for severe footrot in mules where estimates varied greatly over time. The phenotypic correlations between successive scores in SBF ewes were close to 0, genetic correlations were moderately positive (0.18 to 0.55). Correlations in mules were generally of a similar size, but some genetic correlations were higher (up to 0.92). There was a clear trend for heritabilities for lesions and severe lesions to increase with higher prevalence of lesions, even when analysed in a threshold model. Heritability estimates for traits that combine scores over several events in mules, identifying the more persistently affected animals, ranged from 0.12 to 0.23 with the highest estimates for the average number of feet that were (severely) affected in animals scored for a minimum at two events. The heritability of all lesion traits in lambs was estimated as 0. It is concluded that selection for lower lesions is possible in ewes but not lambs, and that a simple binary score at an animal level is at least as effective as a comprehensive score at hoof level. Given the low repeatability of lesion scores, repeated measures over time will improve effectiveness of selection. Selection across environments (flocks, seasons) with different prevalences of lesions scores will need to take account of variation in the heritability.     

Genetic parameters of coat colour in golden fox (Vulpes vulpes L.)

Genetic parameters (heritability, genetic and phenotypic correlations) of chosen coat colour traits of golden fox were estimated. 1013 animals, born on the Sniaty fox farm (Poland) in 1985-1999 were evaluated. In 1993-1999 colour type was additionally assessed for 833 animals, by detailed evaluation of coat colour on the back and sides of the body, throat colour, belly colour and the amount of silver hair. The REML method was used to estimate genetic (co)variance components. Data were transformed using the probit transformation. Heritability estimates for coat traits were low (0.04 to 0.22). Values of most of the estimated genetic parameters (h2, rG, rP) were comparable to those frequently reported for other colour types of silver fox.     

Identity-by-descent-based heritability analysis in the Northern Finland Birth Cohort

For most complex traits, only a small proportion of heritability is explained by statistically significant associations from genome-wide association studies (GWAS). In order to determine how much heritability can potentially be explained through larger GWAS, several different approaches for estimating total narrow-sense heritability from GWAS data have recently been proposed. These methods include variance components with relatedness estimates from allele-sharing, variance components with relatedness estimates from identity-by-descent (IBD) segments, and regression of phenotypic correlation on relatedness estimates from IBD segments. These methods have not previously been compared on real or simulated data. We analyze the narrow-sense heritability of nine metabolic traits in the Northern Finland Birth Cohort (NFBC) using these methods. We find substantial estimated heritability for several traits, including LDL cholesterol (54 % heritability), HDL cholesterol (46 % heritability), and fasting glucose levels (39 % heritability). Estimates of heritability from the regression-based approach are much lower than variance component estimates in these data, which may be due to the presence of strong population structure. We also investigate the accuracy of the competing approaches using simulated phenotypes based on genotype data from the NFBC. The simulation results substantiate the downward bias of the regression-based approach in the presence of population structure.     

Heritability estimates for carcass traits of cattle: a review

We present estimates of heritability for carcass traits of cattle published in the scientific literature. Seventy-two papers published from 1962 to 2004, which reported estimates of heritability for carcass traits, were reviewed. The unweighted means of estimates of heritability for 14 carcass traits by slaughter end point (age, weight, and fat depth) were calculated. Among the three end points, carcass weight, backfat thickness, longissimus muscle area, and marbling score were the carcass traits with the most estimates of heritability (56 相似文献   

Evidence for Genetic Variation in Human Mate Preferences for Sexually Dimorphic Physical Traits

Intersexual selection has been proposed as an important force in shaping a number of morphological traits that differ between human populations and/or between the sexes. Important to these accounts is the source of mate preferences for such traits, but this has not been investigated. In a large sample of twins, we assess forced-choice, dichotomous mate preferences for height, skin colour, hair colour and length, chest hair, facial hair, and breast size. Across the traits, identical twins reported more similar preferences than nonidentical twins, suggesting genetic effects. However, the relative magnitude of estimated genetic and environmental effects differed greatly and significantly between different trait preferences, with heritability estimates ranging from zero to 57%.     

A multi-marker test based on family data in genome-wide association study

Background

Requirements for successful implementation of multivariate animal threshold models including phenotypic and genotypic information are not known yet. Here simulated horse data were used to investigate the properties of multivariate estimators of genetic parameters for categorical, continuous and molecular genetic data in the context of important radiological health traits using mixed linear-threshold animal models via Gibbs sampling. The simulated pedigree comprised 7 generations and 40000 animals per generation. Additive genetic values, residuals and fixed effects for one continuous trait and liabilities of four binary traits were simulated, resembling situations encountered in the Warmblood horse. Quantitative trait locus (QTL) effects and genetic marker information were simulated for one of the liabilities. Different scenarios with respect to recombination rate between genetic markers and QTL and polymorphism information content of genetic markers were studied. For each scenario ten replicates were sampled from the simulated population, and within each replicate six different datasets differing in number and distribution of animals with trait records and availability of genetic marker information were generated. (Co)Variance components were estimated using a Bayesian mixed linear-threshold animal model via Gibbs sampling. Residual variances were fixed to zero and a proper prior was used for the genetic covariance matrix.

Results

Effective sample sizes (ESS) and biases of genetic parameters differed significantly between datasets. Bias of heritability estimates was -6% to +6% for the continuous trait, -6% to +10% for the binary traits of moderate heritability, and -21% to +25% for the binary traits of low heritability. Additive genetic correlations were mostly underestimated between the continuous trait and binary traits of low heritability, under- or overestimated between the continuous trait and binary traits of moderate heritability, and overestimated between two binary traits. Use of trait information on two subsequent generations of animals increased ESS and reduced bias of parameter estimates more than mere increase of the number of informative animals from one generation. Consideration of genotype information as a fixed effect in the model resulted in overestimation of polygenic heritability of the QTL trait, but increased accuracy of estimated additive genetic correlations of the QTL trait.

Conclusion

Combined use of phenotype and genotype information on parents and offspring will help to identify agonistic and antagonistic genetic correlations between traits of interests, facilitating design of effective multiple trait selection schemes.     

Genetic variability for root hair traits as related to phosphorus status in soybean

Plant root hairs are believed to be very important for phosphorus (P) uptake from the soil by expanding the absorptive surface area of the root and increasing the soil volume explored by the roots, but genetic information about root hair traits in soybean is relatively scarce. In the present study, two contrasting genotypes of soybean (Glycine max and Glycine soja), CN4 and XM6, and their 88 F₉-derived recombinant inbred lines (RILs) were grown in a field with moderately low P availability. Some important root hair traits, including root hair density (RHD), average root hair length (ARHL), and root hair length per unit root (RHLUR) were investigated and quantified with an automatic image analysis system and the genetic variability for these root hair traits was estimated with the RIL population. The results indicated that the two parental genotypes differed significantly in the three root hair traits measured, with XM6 generally having larger RHD and RHLUR (but smaller ARHL) than CN4, which may in part explain the difference in biomass and P status between the two parents. All the three root hair traits were continually segregated in the progenial RIL population with a normal distribution of the phenotypic values, indicating that these traits are possibly controlled by quantitative trait loci (QTLs). Analysis of variance for the RIL population showed that RHD had a low heritability (h² _b = 27.32, 31.04, 33.97% for basal roots, tap roots, total roots, respectively), while ARHL had a relatively higher genetic variance and hence a higher heritability (h² _b = 53.85, 59.18, 60.98% for basal roots, tap roots, total roots, respectively), suggesting that RHD is influenced more by environmental factors than ARHL. Both RHD and ARHL were positively correlated with RHLUR, indicating that the former two traits may be the attributes to the latter. On the other hand, RHD and ARHL were negatively correlated with each other, implying a possible complementary relationship between the two traits. Both RHD and RHLUR (but not ARHL) were positively correlated with P concentration in the plant, suggesting an important role of root hairs in P status. The basal roots had denser and higher total root hair length than the tap roots, and this is in accordance with previous observations with other plants that basal roots are more effective for P uptake than tap roots in cultivated soils.     

Heritability of fresh fruit bunch yield and its components in the oil palm (Elaeis guineensis,Jacq.)

Summary Single-plant heritability estimates of 38.9%, 31.5% and 42.3% were obtained for number of bunches (NB), fresh fruit bunch yield (FFB) and mean bunch weight (MBW) respectively. Hybrid (family) mean heritability estimates for these traits were 88.9%, 90.5% and 96% respectively. Repeatability estimates for these traits were 33%, 11% and 8% for NB, FFB and MBW respectively. Evaluation of hybrid family mean for yield components appears feasible at the third or fourth year of data collection. Phenotypic and genotypic correlations between NB and FFB were 0.80 and 0.61 respectively; between NB and MBW, –0.41 and –0.16 respectively; and between FFB and MBW, 0.66 and 0.60 respectively. The hypothesis that increased FFB can be obtained by hybridization between parents with high NB and heavy MBW is supported by this correlation set.     

Sweat pore count, hair density and tooth size: heritability and genetic correlation

In 109 subjects from 50 families without major inherited disorders, sweat pore count showed the anticipated reduction with age but also unexpected systematic differences between sides and between fingers. After adjustment for age and sex, significant genetic variation was found for sweat pore count, hair density and tooth size. The three traits were not phenotypically correlated but there was a significant negative genetic correlation between hair density and sweat pore count. The findings suggest that the same genes influence these two traits in opposite directions and that genetic and environmental influences may act on them through different physiological mechanisms.     

Quantitative conservation genetics of wild and managed bees

Quantitative genetic traits provide insights into the evolutionary potential of populations, as heritability estimates measure the population’s ability to respond to global changes. Although wild and managed bees are increasingly threatened by the degradation of natural habitats and climate change, risking plant biodiversity and agriculture production, no study has yet performed a systematic review of heritability estimates across the group. Here we help fill this knowledge gap, gathering all available heritability estimates for ants, bees, and wasps, evaluating which factors affect these estimates and assessing the reported genetic correlations between traits. Using a model selection approach to analyze a dataset of more than 800 heritability estimates, we found that heritability is influenced by trait type, with morphological traits exhibiting the highest heritability estimates, and defense and metabolism-related traits showing the lowest estimates. Study system, sociality degree, experimental design, estimation type (narrow or broad-sense heritability), and sample size were not found to affect heritability estimates. Results remained unaltered when correcting for phylogenetic inertia, and when analyzing social bees separately. Genetic correlations between honeybee traits revealed both positive coefficients, usually for traits in the same category, and negative coefficients, suggesting trade-offs among other traits. We discuss these findings and highlight the importance of maintaining genetic variance in fitness-related traits. Our study shows the importance of considering heritability estimates and genetic correlations when designing breeding and conservation programs. We hope this meta-analysis helps identify sustainable breeding approaches and conservation strategies that help safeguard the evolutionary potential of wild and managed bees.     

Multifactorial analysis of a mixed-longitudinal sample of Indian siblings: Age and sex effects on heritability

The aim of the present study was to examine the heritability of 11 traits in a mixed-longitudinal sample of Indian siblings, and to determine whether heritability estimates vary during the growth period and whether they are influenced by sex. The sample consisted of 245 brothers and 213 sisters from 138 nuclear families living in a semi-urban area in Kolkata, India. The age ranged between 5 and 19 years. The traits were standardised for age and sex using standard deviation scores (SDS) produced by the LMS method (Cole, T.J., 1988. Fitting smoothed centile curves to reference data. J. R. Stat. Soc. A 151, 385-418). The standard deviation scores were analysed by PCA. The two factors with eigenvalues above 1 explained 77.3% of the variance; they showed a high level of pleiotropism present among the studied traits and represented body lengths (PC1) and body weight and breadths (PC2). The heritability between all types of siblings (irrespective of sex) for the PC1 and PC2 was estimated. The heritability between various pairs of siblings showed variations along the whole ontogenetic period studied. During the childhood and pre-pubertal period, heritability between brothers, brother-sister pairs and any sibling pairs was mostly constant, with small and non-significant variations. All the pairs showed the lowest degree of heritability during puberty for PC1 but not for PC2, with significant changes of heritability estimates between adolescence and adulthood, in most of the analysed sibling pairs and in both PC factors. The highest heritability was generally observed at the end of the examined growth period in all pairs. A significant effect of sex on heritability was only detected for PC2 at 11 years of age.     

Heritability of phenotypic udder traits to improve resilience to mastitis in Texel ewes

There are no estimates of the heritability of phenotypic udder traits in suckler sheep, which produce meat lambs, and whether these are associated with resilience to mastitis. Mastitis is a common disease which damages the mammary gland and reduces productivity. The aims of this study were to investigate the feasibility of collecting udder phenotypes, their heritability and their association with mastitis in suckler ewes. Udder and teat conformation, teat lesions, intramammary masses (IMM) and litter size were recorded from 10 Texel flocks in Great Britain between 2012 and 2014; 968 records were collected. Pedigree data were obtained from an online pedigree recording system. Univariate quantitative genetic parameters were estimated using animal and sire models. Linear mixed models were used to analyse continuous traits and generalised linear mixed models were used to analyse binary traits. Continuous traits had higher heritabilities than binary with teat placement and teat length heritability (h²) highest at 0.35 (SD 0.04) and 0.42 (SD 0.04), respectively. Udder width, drop and separation heritabilities were lower and varied with udder volume. The heritabilities of IMM and teat lesions (sire model) were 0.18 (SD 0.12) and 0.17 (SD 0.11), respectively. All heritabilities were sufficiently high to be in a selection programme to increase resilience to mastitis in the population of Texel sheep. Further studies are required to investigate genetic relationships between traits and to determine whether udder traits predict IMM, and the potential benefits from including traits in a selection programme to increase resilience to chronic mastitis.     

家蚕二化性杂交品种部分数量性状遗传参数的初步评估

采用完全随机设计法根据10头老熟幼虫体重、全茧重、茧层量、茧层率（%）、存活率、万蚕茧层量和茧丝长等指标,对两对二化性家蚕Bombyx mori L. 杂交品系（SH6×NB₄D₂和CSR₂×CSR₄）杂交一代的22个子代个体进行了遗传参数估算,以缩小优质蚕品种的候选范围,并且计算出直接筛选的参数,如遗传力和遗传进度等,使这些信息可用于以筛选高产新品种为目的的育种和选择过程中。杂交子代2, 4, 5, 6, 7, 10, 14, 16, 19和20号个体在这几个指标中表现出显著的优越性。全茧重、万蚕茧层量和茧丝长的遗传力和遗传进度较大,可以简单地从表现型的差异对这些性状进行选择并取得遗传性状改良。其他几个指标(10头老熟幼虫体重、茧层量、茧层率(%)和存活率)的遗传力和遗传进度较低,对这些性状进行直接选择来改良品种的效果较差。