Rodríguez-Almeida F A, Van Vleck L D, Willham R L, Northcutt S L
Department of Animal Science, University of Nebraska, Lincoln 68583, USA.
J Anim Sci. 1995 Apr;73(4):1002-11. doi: 10.2527/1995.7341002x.
Dominance and additive x additive genetic variances were estimated for birth and weaning traits of calves from three synthetic lines of beef cattle differing in mature size. Data consisted of 3,992 and 2,877 records from lines of small-, medium-, and large-framed calves in each of two research herds located at Rhodes and McNay, IA, respectively. Variance components were estimated separately by herd and line for birth weight (BWT), birth hip height (BH), 205-d weight (WW), and 205-d hip height (WH) by derivative-free REML with an animal model. Model 1 included fixed effects of year, sex, and age of dam. Random effects were additive direct (a) and additive maternal (m) genetic with covariance (a,m), maternal permanent environmental, and residual. Model 2 also included dominance (d) and model 3 included dominance plus additive x additive (a:a) effects. In general, only slight changes occurred in other variance components estimates when day was included in Model 2. However, large estimates of additive x additive genetic variances obtained with Model 3 for 4 out of 24 analyses were associated with reductions in estimates of direct additive variances. Direct (maternal) heritability estimates averaged across herd-line combinations with Model 2 were .53(.11), .42(.04), .27(.12), and .35(.04) for BWT, BH, WW, and WH, respectively. Corresponding covariance (a,m) estimates as fractions of phenotypic variance (sigma p2) were .00, .01, .01, and .06, respectively. For maternal permanent environmental effects in Model 2, average estimates of variances as fractions of sigma p2 across herd-line combinations were .03, .00, .05, and .02, for BW, BH, WW, and WH, respectively. Dominance effects explained, on average, 18, 26, 28, and 11% of total variance for BWT, BH, WW, and WH, respectively. Most of the estimates for additive x additive variances were negligible, except for one data set for BWT, two for BH, and one for WH, where the relative estimates of this component were high (.21 to .45). These results suggest that most of the non-additive genetic variance in the traits studied is accounted for by dominance genetic effects.
对来自三个成熟体型不同的肉牛合成系的犊牛出生和断奶性状的显性遗传方差以及加性×加性遗传方差进行了估计。数据分别来自位于爱荷华州罗兹和麦克奈的两个研究牛群中，小型、中型和大型体格犊牛系的3992条和2877条记录。采用无导数REML和动物模型，按牛群和品系分别估计出生体重（BWT）、出生时髋高（BH）、205日龄体重（WW）和205日龄髋高（WH）的方差分量。模型1包括年份、性别和母牛年龄的固定效应。随机效应包括加性直接（a）和加性母体（m）遗传效应及其协方差（a,m）、母体永久环境效应和残差效应。模型2还包括显性（d）效应，模型3包括显性效应加上加性×加性（a:a）效应。一般来说，当模型2中纳入天数时，其他方差分量估计值仅有轻微变化。然而，在24次分析中有4次，模型3得到的加性×加性遗传方差的估计值较大，这与直接加性方差估计值的降低有关。模型2中，牛群-品系组合的直接（母体）遗传力估计值，BWT、BH、WW和WH分别平均为0.53（0.11）、0.42（0.04）、0.27（0.12）和0.35（0.04）。协方差（a,m）估计值占表型方差（sigma p2）的比例分别为0.00、0.01、0.01和0.06。对于模型2中的母体永久环境效应，牛群-品系组合的方差估计值占sigma p2的比例，BW、BH、WW和WH分别平均为0.03、0.00、0.05和0.02。显性效应分别平均解释了BWT、BH、WW和WH总方差的18%、26%、28%和11%。除了一个BWT数据集、两个BH数据集和一个WH数据集外，大多数加性×加性方差的估计值可以忽略不计，在这些数据集中，该分量的相对估计值较高（0.21至0.45）。这些结果表明，所研究性状的大多数非加性遗传方差是由显性遗传效应造成的。
