多个典范选择性状的综合优化研究

利用综合优化方法,研究了在育种目标约束下,选择性状表现型向量与目标性状基因型向量的典范相关,提出了综合典范性状对的数学模型。综合典范性状对是Ｓ个间撞遗传系数较在的典范选择－目标性状对,在育种目标约束下间接遗传系数极大化的线性组合。综合典范选择性状,作为间接选择的指标,有较好地满足多目标育种的要求。     

多个主成分性状的综合优化研究

考虑育种目标的要求,对多个独立的主成分性状进行综合优化,建立了综合主成分性状的数学模型．综合主成分性状是S个表型方差（遗传方差）最大的主成分性状在育种目标约束下表型方差（或遗传方差）极大化下的线性组合,作为育种指标,选择效果好,预见性强．     

关于多个数量性状的典范相关研究 Ⅰ.典范性状及其遗传力

本文用多元统计分析方法,研究多个数量性状的表现型变量与基因型变量的相关关系,提出了典范性状及其遗传力的概念。第一典范性状是测量性状的所有线性组合中具有最大遗传力的线性组合,第i典范性状则是在与前面i—1个典范性状不相关的那些性状的线性组合中具有最大遗传力的线性组合。在实际问题中,只须取少数典范性状进行研究就能充分利用试验所提供的信息。提出了估计典范性状及其遗传力的方法,并讨论了典范性状在遗传育种研究中应用的可能性。     

比值性状的遗传力与选择强度的关系

本文利用计算机模拟技术比较了不同遗传参数组织下比值性状的理论遗传力及其在各选择强度下实现遗传力的差异,证明了比值性状的遗传特性与一般正态数量性状不同,其实现遗传传力随选择强度不同而呈有规律的顺序变化;并且这种变化受比值的两个分量性状的遗传力和遗传相关大小影响。Ｓｕｔｈｅｒｌａｎｄ的理论遗传力亦不能有效地预测选择比值的遗传变化。反求指数法（ＩＩＲ法）对直接选择比值的作用机制分析表明,在不同选择强度下     

杂交粳稻品质与产量性状间的典范相关分析──杂交粳稻品质性状的遗传研究Ⅳ

由38个杂交粳稻及其12个亲本的6个产量性状和13个品质性状的典范相关分析得出：两者以稻谷重、糙米重、精米重、每穗实粒数、单株产量间相关极显著．其它性状关系小．故对产量及其余品质性状同步选择可加速育成优质高产组合．提高产量宜着力增加穗数和结实粒数,籽粒不且过大过宽过重．改良品质以糙米率、糙米长宽比、垩白率、透明度、食味最为关键,并互为正向关系,可同时改良,其中透明度、垩白率又是影响食味的主要直观性状．     

氮素水平对籼、粳稻主要数量性状遗传力的影响

本文在0、35、75、105公斤/公顷4个纯氮水平下,考察了籼、粳稻各10个品种株高、结实率等12个主要数量性状遗传力的变化规律。结果表明,性状不同,其遗传力受氮素的影响程度也不同,两亚种皆然,但籼稻的遗传力均比粳稻的高,籼稻群体比粳稻群体更具遗传多样性。因此,育种实践中,应将目标性状设在最宜于其遗传信息充分表达的氮素水平下进行选择。     

二棱大麦数量性状相关遗传力和选择指数的分析

以15个二棱大麦品种(系)材料,用相关遗传力研究大麦数量性状的相关遗传,并计算分析籽粒产量和产量构成性状所组合的各种选择指数。结果表明:各性状与单株粒重的相关遗传力均低于单株粒重的遗传力,故仅利用一个性状作间接选择的效率比对单株粒重作直接选择的效率低;在构成大麦产量的三要素中,着重提高单株穗数对产量的选择效率最大; 高产育种同时考虑与产量显著相关的性状比单纯对产量选择的效果好,其中以单株穗数、每穗粒数和籽粒产量结合起来选择的效果最佳。本文并对相关遗传力在相关遗传变异分析中的应用进行了讨论。     

氮素水平对釉、粳稻主要数量性状遗传力的影响

本文在0、35、75、105公斤／公顷4个纯氮水平下,考察了仙、粳稻各10个品种株高、结实率等12个主要数量性状遗传力的变化规律。结果表明,性状不同,其遗传力受氮素的影响程度也不同,两亚种皆然,但釉稻的遗传力均比粳稻的高,釉稻群体比粳稻群体更具遗传多样性。因此,育种实践中,应将目标性状设在最宜于其遗传信息充分表达的氮素水平下进行选择。     

基于多性状模型内蒙古绒山羊早期生长性状基因组预测准确性研究

内蒙古绒山羊是经过长期自然选择和人工选育后形成的优良家畜品种,是目前世界一流的绒肉兼用山羊。多性状动物模型被认为可以显著提高畜禽遗传评估的准确性,实现性状间的间接选择。本文基于内蒙古绒山羊个体的系谱、基因型、环境以及早期生长性状的表型记录,建立多性状动物模型,利用ABLUP、GBLUP、ssGBLUP三种方法进行早期生长性状(初生重、断乳重、断乳前平均日增重、周岁重)遗传参数及基因组育种值的估计,进一步利用五倍交叉验证方法评价基因组育种值估计准确性和可靠性。结果显示,3种方法估计的初生重遗传力为0.13～0.15,断乳重遗传力为0.13～0.20,日增重遗传力为0.11～0.14,周岁重遗传力为0.09～0.14,均属于中等偏低遗传力;断乳重和日增重、日增重和周岁重之间存在强的正遗传相关,相关系数分别为0.77～0.79和0.56～0.67,表型相关发现同样的规律;ABLUP、GBLUP和ssGBLUP法估计的初生重育种值准确性分别为0.5047、0.6694、0.7156,断乳重分别为0.6207、0.6456、0.7254;日增重分别为0.6110、0.6855、0.7357,周岁...     

性状遗传力与QTL方差对标记辅助选择效果的影响

在采用动物模型标记辅助最佳线性无偏预测方法对个体育种值进行估计的基础上,模拟了在一个闭锁群体内连续对单个性状选择10个世代的情形,并系统地比较了性状遗传力和QTL方差对标记辅助选择所获得的遗传进展、QTL增效基因频率和群体近交系数变化的影响。结果表明：在对高遗传力和QTL方差较小的性状实施标记辅助选择时,可望获得更大的遗传进展;遗传力越高,QTL方差越大,则QTL增效基因频率的上升速度越快;遗传力较高时,群体近交系数上升的速度较为缓慢,而QTL方差对群体近交系数上升速度的影响则不甚明显。结合前人关于标记辅助选择相对效率的研究结果,可以认为：当选择性状的遗传力和QTL方差为中等水平时,标记辅助选择可望获得理想的效果。     

Bias in the prediction of genetic gain due to mass and half-sib selection in random mating populations

The prediction of gains from selection allows the comparison of breeding methods and selection strategies, although these estimates may be biased. The objective of this study was to investigate the extent of such bias in predicting genetic gain. For this, we simulated 10 cycles of a hypothetical breeding program that involved seven traits, three population classes, three experimental conditions and two breeding methods (mass and half-sib selection). Each combination of trait, population, heritability, method and cycle was repeated 10 times. The predicted gains were biased, even when the genetic parameters were estimated without error. Gain from selection in both genders is twice the gain from selection in a single gender only in the absence of dominance. The use of genotypic variance or broad sense heritability in the predictions represented an additional source of bias. Predictions based on additive variance and narrow sense heritability were equivalent, as were predictions based on genotypic variance and broad sense heritability. The predictions based on mass and family selection were suitable for comparing selection strategies, whereas those based on selection within progenies showed the largest bias and lower association with the realized gain.     

Heritability and physiological correlates of migratory tendency in the grasshopper Melanoplus sanguinipes

Abstract. Durations of tethered flights by the North American migratory grasshopper Melanoplus sanguinipes Fabricius are bimodally distributed: most individuals either will not fly, or else will fly for many hours. This observation suggests a simple measure (the ‘one‐hour rule’) for distinguishing migrants from non‐migrants. This measure is repeatable (repeatability = 0.6–0.7). Using laboratory‐reared offspring of grasshoppers from an Arizona population of mixed migratory tendency, a breeding experiment was conducted to determine the heritability of migratory tendency and possible correlated responses to selection on migratory behaviour. When migratory tendency is considered as a threshold trait, the heritability of liability is in the range 0.5–0.6. Most families in the breeding experiment had at least some migrants among their offspring; selection on migratory incidence had a correlated effect on the durations of flights by these individuals. The magnitude of thoracic lipid reserves showed a modest correlated response to selection on migratory behaviour. Thoracic and abdominal lipid reserves in identified migrants are reduced by flight, indicating that lipid is mobilized and consumed during flight in this species.     

Body condition score of Nellore beef cows: a heritable measure to improve the selection of reproductive and maternal traits

Despite the economic importance of beef cattle production in Brazil, female reproductive performance, which is strongly associated with production efficiency, is not included in the selection index of most breeding programmes due to low heritability and difficulty in measure. The body condition score (BCS) could be used as an indicator of these traits. However, so far little is known about the feasibility of using BCS as a selection tool for reproductive performance in beef cattle. In this study, we investigated the sources of variation in the BCS of Nellore beef cows, quantified its association with reproductive and maternal traits and estimated its heritability. BCS was analysed using a logistic model that included the following effects: contemporary group at weaning, cow weight and hip height, calving order, reconception together with the weight and scores of conformation and early finishing assigned to calves at weaning. In the genetic analysis, variance components of BCS were estimated through Bayesian inference by fitting an animal model that also included the aforementioned effects. The results showed that BCS was significantly associated with all of the reproductive and maternal variables analysed. The estimated posterior mean of heritability of BCS was 0.24 (highest posterior density interval at 95%: 0.093 to 0.385), indicating an involvement of additive gene action in its determination. The present findings show that BCS can be used as a selection criterion for Nellore females.     

Genetic analysis of the temperament of Nellore cattle using linear and threshold models

Temperament is an important trait for the management and welfare of animals and for reducing accidents involving people who work with cattle. The present study aimed to estimate the genetic parameters related to the temperament score (T) and weaning weight (WW) of Nellore cattle, reared in a beef cattle breeding program in Brazil. Data were analyzed using two different two-trait statistical models, both considering WW and T: (1) a linear-linear model in which variance components (VCs) were estimated using restricted maximum likelihood; and (2) a linear-threshold model in which VCs were estimated via Bayesian inference. WW was included in the analyses of T to minimize any possible effects of sequential selection and to allow for estimation of the genetic correlation between these two traits. The heritability estimates for T were 0.21±0.003 (model 1) and 0.26 (model 2, with a 95% credibility interval (95% CI) of 0.21 to 0.32). The estimated genetic correlations between WW and T were of a moderate magnitude (−0.33±0.01 (model 1) and −0.34 (95% CI: −0.40, −0.28, model 2). The genetic correlations between the estimated breeding values (EBVs) obtained for the animals based on the two models were high (>0.92). The use of different models had little influence on the classification of animals based on EBVs or the accuracy of the EBVs.     

Improving the analysis of low heritability complex traits for enhanced genetic gain in potato

Key message

Best linear unbiased prediction (BLUP), which uses pedigree to estimate breeding values, can result in increased genetic gains for low heritability traits in autotetraploid potato.

Abstract

Conventional potato breeding strategies, based on outcrossing followed by phenotypic recurrent selection over a number of generations, can result in slow but steady improvements of traits with moderate to high heritability. However, faster gains, particularly for low heritability traits, could be made by selection on estimated breeding values (EBVs) calculated using more complete pedigree information in best linear unbiased prediction (BLUP) analysis. One complication in applying BLUP predictions of breeding value to potato breeding programs is the autotetraploid inheritance pattern of this species. Here we have used a large pedigree, dating back to 1908, to estimate heritability for nine key traits for potato breeding, modelling autotetraploid inheritance. We estimate the proportion of double reduction in potatoes from our data, and across traits, to be in the order of 10 %. Estimates of heritability ranged from 0.21 for breeder’s visual preference, 0.58 for tuber yield, to 0.83 for plant maturity. Using the accuracies of the EBVs determined by cross generational validation, we model the genetic gain that could be achieved by selection of genotypes for breeding on BLUP EBVs and demonstrate that gains can be greater than in conventional schemes.     

The accuracy of a heritability estimator using molecular information

The heritability of a quantitative trait is a key parameter to quantify the genetic variation present in a population. Although estimates of heritability require accurate information on the genetic relationship among individuals, pedigree data is generally lacking in natural populations. Nowadays, the increasing availability of DNA markers is making possible the estimation of coancestries from neutral molecular information. In 1996, K. Ritland developed an approach to estimate heritability from the regression of the phenotypic similarity on the marker-based coancestry. We carried out simulations to analyze the accuracy of the estimates of heritability obtained by this method using information from a variable number of neutral codominant markers. Because the main application of the estimator is on populations with no family structure, such as natural populations, its accuracy was tested under this scenario. However, the method was also investigated under other scenarios, in order to test the influence of different factors (family structure, assortative mating and phenotypic selection) on the precision. Our results suggest that the main factor causing a directional bias in the estimated heritability is the presence of phenotypic selection, and that very noisy estimates are obtained in the absence of a familiar structure and for small population sizes. The estimated heritabilities from marker-based coancestries showed lower accuracy than the estimated heritabilities from genealogical coancestries. However, a large amount of bias occurred even in the most favourable situation where genealogical coancestries are known. The results also indicate that the molecular markers are more suitable to infer coancestry than inbreeding.     

Variation in the hematocrit of a passerine bird across life stages is mainly of environmental origin

The heritability of the hematocrit in adult, breeding pied flycatchers Ficedula hypoleuca is examined in a southern European population across seven years to see the consistency, or lack thereof, of patterns found with the trait at fledgling age where no significant heritability could be detected. While the across-years repeatability of the trait in adult, breeding birds was low but significant, heritabilities based on adult parent-adult offspring regressions controlling for assortative mating and full-sibling comparisons did not differ significantly from zero. Neither were heritability estimates affected by selection on fledgling hematocrit, as it was unrelated to local recruitment. There was no relationship between fledgling and adult hematocrit, suggesting that both behave as phenotypically plastic, different traits. This is the first study testing for the heritability of a physiological trait in birds with data from adult, free-ranging individuals.