(4 Points) Construct to scale a diagram (likethe one used in lecture for calf weaning weights) showing the following hypothetical sample of records for live (market) weight in lambs (assume = 130 lb ). Be sure to lobel completely. Lambs 1 and 3 have similar market weights, but for different reasons. Briefly, explain. A New Model The basic genetic model for quantitative traits can now be expanded to include breeding value (BV) and gene combination value (GCV): P = + B V + GC V + E The weaning weights of the three calves depicted in Figure 1 are shown again in Figure 4, this time with their (hypothetical) breeding values and gene combination values included. Calf \#1 has the heaviest weaning weight, but note that most of his superior performance is due to either environment or genetic effects that cannot be transmitted to offspring. If heavier weaning weights are desirable, the best breeding animal should be Calf \#3. Despite his mediocre individual performance, he has the highest breeding value. Figure 4. Contributions of breeding value, gene combination value, and environmental effect to the weaning weights of the three calves depicted in Figure 1. The new model for quantitative traits retains many of the characteristics of the basic model. Like genotypic value, breeding value and gene combination value are expressed as positive and negative deviations from a population mean. The average of breeding values and the average of gene combination values across an entire population are, therefore, zero. Furthermore, breeding values and gene combination values are considered independent of environment effects and each other. It is possible to have highly inbred animals that suffer inbreeding depression (unfavorable gene combination value) and, Calf \#1 weighs 600 lb (100 lb above average), has a higher then average genotypic value ( l ), and experienced a better than averoge environmental effect ( 5 ). Colf m2 weighs 450 lb ( 50 lb below average), has a lower than average genotypic value, and experienced a worse than average environmental effect. Calf 3 weighs 460 lb . His genotypic volue for weaning weight is higher than average, but his actual performance is below average due to a very poor environment. Figure 5. Contributions of components of the genetic model for repeated traits for tw o records on a single dairy cow for 305-d lactation yield. Appendix B Partitioning the Genotypic Value Where is the breeding value? As defined in the body of this section, the basic genetic model for quantitative traits is: P = + G + E where P = the phenotypic value or performance of an individual animal for a particular trait. = (Greek letter m u ) the population mean or average phenotypic value for the trait for all animals in the population. G m the genotypic value of the individual for the trait. E = the environmental effect on the individual's performance for the trait. We said this model would help us understand breeding value, which we defined as the value .

1. (4 Points) Construct to scale a diagram (likethe one used in lecture for calf weaning weights)
showing the following hypothetical sample of records for live (market) weight in lambs (assume
= 130 lb ). Be sure to lobel completely. Lambs 1 and 3 have similar market weights, but for
different reasons. Briefly, explain. A New Model The basic genetic model for quantitative traits
can now be expanded to include breeding value (BV) and gene combination value (GCV): P = +
B V + GC V + E The weaning weights of the three calves depicted in Figure 1 are shown again
in Figure 4, this time with their (hypothetical) breeding values and gene combination values
included. Calf #1 has the heaviest weaning weight, but note that most of his superior
performance is due to either environment or genetic effects that cannot be transmitted to
offspring. If heavier weaning weights are desirable, the best breeding animal should be Calf #3.
Despite his mediocre individual performance, he has the highest breeding value. Figure 4.
Contributions of breeding value, gene combination value, and environmental effect to the
weaning weights of the three calves depicted in Figure 1. The new model for quantitative traits
retains many of the characteristics of the basic model. Like genotypic value, breeding value and
gene combination value are expressed as positive and negative deviations from a population
mean. The average of breeding values and the average of gene combination values across an
entire population are, therefore, zero. Furthermore, breeding values and gene combination values
are considered independent of environment effects and each other. It is possible to have highly
inbred animals that suffer inbreeding depression (unfavorable gene combination value) and, Calf
#1 weighs 600 lb (100 lb above average), has a higher then average genotypic value ( l ), and
experienced a better than averoge environmental effect ( 5 ). Colf m2 weighs 450 lb ( 50 lb
below average), has a lower than average genotypic value, and experienced a worse than average
environmental effect. Calf 3 weighs 460 lb . His genotypic volue for weaning weight is higher
than average, but his actual performance is below average due to a very poor environment.
Figure 5. Contributions of components of the genetic model for repeated traits for tw o records
on a single dairy cow for 305-d lactation yield. Appendix B Partitioning the Genotypic Value
Where is the breeding value? As defined in the body of this section, the basic genetic model for
quantitative traits is: P = + G + E where P = the phenotypic value or performance of an
individual animal for a particular trait. = (Greek letter m u ) the population mean or average
phenotypic value for the trait for all animals in the population. G m the genotypic value of the
individual for the trait. E = the environmental effect on the individual's performance for the trait.
We said this model would help us understand breeding value, which we defined as the value of
an individual as a contributor of genes to the next generation. But, where is breeding value (BV)
in the model? The only genetic component of the model is the genotypic value (G). Does G equal
BV? The answer is no. To explain why the answer is no, let's look at G in more detail. it
represents the overall effects of an individual's genes, either singly or in combination, on that
individual's performance for a trait. As a result, it can be partitioned into additive (A), dominance
(D), and epistatic (1) genetic components. The basic genetic model can then be rewritten as: P =
+ A + D + I G First, consider A. Additive gene action is the most important type of gene action
in the inheritance of, and selection for, quantitative traits. When gene action is additive, each
allele in the genotype has a specific metric value it adds to the phenotype. The additive genetic
effect of an allele can be either positive or negative, Also, the effect of that allele is independent
of the effect of the other allele at that locus as well as the effects of alleles at all other loci. This
means additive genetic effects are independent gene effects. Only independent gene effects are
directly transmitted to the next generation. [Recall our discussion of Mendelian genetics in
Section II.] Thus, the additive genetic value (A) is equal to the breeding value (BV). B V is the

2. portion of G that is transmitted to offspring; it is due to independent gene effects. Additive gene
effects are independent. Thus, A = B V . Now consider D and I. Both these components of G
have non-additive genetic effects. The effects of dominance and epistasis are due to gene
combinotions and, as such, are not directly transmitted to the next generation. Recall that
dominance is the interaction between alleles at a single locus and epistasis is the interaction of
alleles at different loci (Section II). Thus, neither have independent gene effects.