Animal breeding and inbreeding

Thus far we have evaluated the rate of inbreeding in retrospect. However, as it provides an indication of the expected increase in inbreeding depression, it would be nice to be able to predict the rate of inbreeding in future geThus far we have evaluated the rate of inbreeding in retrospect. However, as it provides an indication of the expected increase in inbreeding depression, it would be nice to be able to predict the rate of inbreeding in future generations. Predicting the exact future is not possible, but you can make an approximation. A simple formula to get some idea about the effect of selection decisions with respect to the number of breeding animals is: In other words, if you know the number of males and females that are used for breeding, you can predict what the rate of inbreeding will be. Of course the exact rate of inbreeding will depend on the genetic relationships between the animals, and that is not taken into account in this formula. And as we have seen in figures 5 and 6, the rate of inbreeding depends on your population size, more than on mating strategy. This formula will provide you with an approximation, assuming that these numbers represent your population size, and assuming absence of selection and no extremely small or large family sizes, relative to the sizes of the other families. For example, let’s assume a population of 3000 animals. But only 20 males and 300 females participate in breeding. Each female gets 10 offspring. What is the rate of inbreeding in this population? So 20 males and 300 females, that is 320 breeding animals, results in a rate of inbreeding of %. Would it matter how these 320 animals were divided across males and females? Try it yourself. What if you would use 160 males and 160 females? And what if you would use 2 males and 318 females? You will find out that the more skewed the proportion of breeding males to females is, the higher the rate of inbreeding. How about population size? Would that matter? What if you would use only one male and one female for breeding? And how would the rate on inbreeding change if you would increase that number to 10 males and 10 females? Or 100 males and 100 females? You will find out that in very small breeding populations the rate of inbreeding can’t be controlled by using equal numbers of males and females for breeding. So far we have assumed that family size, so number of offspring in males and females, is equal for all families. In real life this is not the case. The rate of inbreeding is most influenced by the largest family, because they will have the largest proportion in the next generation(s). We also have assumed that the population size remains constant across generations. In real life this may not always be the case. Populations may decrease in size because of, for example, decrease in popularity or a disease outbreak. They may increase in size because of, for example, an increase in popularity, or a smaller mortality than anticipated. Thus: The rate of inbreeding depends on a combination of the proportion of breeding males to females the number of breeding males and females variation in family size fluctuation in population size Example: rate of inbreeding in the Holstein Friesian Even though the population of Holstein Friesian cattle is very large, so is the average additive genetic relationship among those animals. Because of the use of AI, the number of offspring per sire often is very large. And some sires are used much more for breeding than others, resulting in very unequal family size. Even though Holstein Friesians around the world are related to each other, there is some degree of subpopulations in the different countries. In Denmark, for example, the rate of inbreeding is estimated at 1%, in Ireland at 0.7%, and in the USA at 1.3%. These are very high values, considering the fact that millions of cows are used for breeding, and hundreds of bulls are available. However, only a limited number are used for breeding, and on a very large number of cows. This is a clear example of the effect of very unequal family size (some bulls used much more than others) on the rate of inbreeding. The problem: let’s assume a population of 3000 animals. But only 20 males and 300 females participate in breeding. Each female gets 10 offspring. What is the rate of inbreeding in this population? #Kinship #inbreeding #NikolaysGeneticsLessons #Genetics #Phenotype #Genotype #NarrowSenseHeritability #BroadSenseHeritability #breeding #selection #traits #breedingValue #population #estimatedBreedingValues #Prepotency #pedigree #DNA #quantitativeTrait #populationGenetics #pureLine #selectiveBreeding #ArtificialSelection #phenotypicTraits #breeds #Siamese #hybridCatSpecies #exoticPets #AnimalBreeding