In a population of Arabian race horses the breeding goal is to increase running speed in 2,000 m races for 3 year olds. The average time across this distance at that age in the current population is 117.0 seconds. The plan is to select the best 10% for breeding (for now we ignore the difference between males and females, both in speed and in reproductive capacity). The genetic standard deviation is 3.0 seconds, and the accuracy of selection is 0.24. Predict the genetic gain using these selection decisions. What would be the average 2,000 m time in the next generation?
Answer: Look in the table at the end of the chapter and find that a selected proportion of 10% results in a selection intensity of 1.755. This means that this selected top 10% on average performs 1.755 standard deviations better than the population average. It will depend on the variance for the trait how much better that is in trait units: 1.755 *3.0 = 5.265 seconds. This is a bit optimistic because we were not able to estimate the genetic potential 100% accurately. In fact, it was only 24% accurate (rIH = 0.24). Combining all information results in: ΔG = i * rIH * σa = 1.755 * 0.24 * 0.3 = 1.26 seconds. The example is about improving running speed, so the next generation will be 1.26 sec faster: 117.0 – 1.26 = 115.74 seconds.