GENETIC MANAGEMENT OF DOG BREEDS
THE BASICS
In large, widely dispersed populations of wild animals and plants that are free of disturbance from humans, nature is the only force of selection. The fittest survive and the unfit die, creating populations that are robust in the face of environmental changes and disease. A population that is small or isolated, however, is vulnerable. Over time, the population becomes more and more inbred, and just by chance alone alleles are lost from the gene pool (genetic drift). As individuals become more and more similar to each other genetically, the risk to the population increases - a rare virus, or an unusual cold snap or heat wave, could wipe out an entire population.
In many ways, purebred dogs are similar to endangered species or to captive populations such as livestock or zoo animals. If they are in closed populations (i.e., no new animals are added, such as a for closed studbook), they must inevitably become more inbred over time, and they will lose genetic diversity through genetic drift. If at the same time breeding is controlled so that only some animals breed and mating is not random (i.e. a breeder determines who mates with whom), loss of genetic diversity can be extremely rapid. As breeders seek to produce animals that are more uniform as they are selecting for type, the resulting homozygosity makes the population more vulnerable. At the extreme, all individuals in the population would become genetically identical. Then of course, breeders would have no differences between animals to select for, and a novel pathogen could exterminate an entire breed.
The two basic goals of genetic management are to control the loss of genetic resources from a population, and to use breeding strategies that maintain a healthy population of animals that meets the needs of the breeders. The principles are the same for dogs as they are for cheetahs, horses, chickens, fish, or even plants. Fortunately, excellent tools have been developed over the last 20 years by population and conservation geneticists that have revolutionized the breeding of domestic animals including dogs.
POPULATION GENETICS
Genetic management requires the ability to understand how the frequency and distribution of genes in a population change over time. In fact, the field of population genetics was developed by biologists trying to understand the processes of evolution and adaptation, and it has since been put to good use by conservation geneticists and animal breeders in the management of captive populations.
The changes in the traits of a dog breed over time are also a form of evolution - through reproduction and selection (both controlled by the breeder), some alleles become more frequent in the breed and some become less frequent or are even eliminated. If we have some basic information about the population of interest - the number of individuals, sex ratio, how often they breed, the number of offspring they have, how long they live, and so on - we can predict how the frequencies of alleles will change from one generation to the next using statistics and probability. As you read about population genetics you will run into lots of complicated looking equations. Our computers do all the math for us now, and you only need to understand what they mean and how they work in general.
In large, widely dispersed populations of wild animals and plants that are free of disturbance from humans, nature is the only force of selection. The fittest survive and the unfit die, creating populations that are robust in the face of environmental changes and disease. A population that is small or isolated, however, is vulnerable. Over time, the population becomes more and more inbred, and just by chance alone alleles are lost from the gene pool (genetic drift). As individuals become more and more similar to each other genetically, the risk to the population increases - a rare virus, or an unusual cold snap or heat wave, could wipe out an entire population.
In many ways, purebred dogs are similar to endangered species or to captive populations such as livestock or zoo animals. If they are in closed populations (i.e., no new animals are added, such as a for closed studbook), they must inevitably become more inbred over time, and they will lose genetic diversity through genetic drift. If at the same time breeding is controlled so that only some animals breed and mating is not random (i.e. a breeder determines who mates with whom), loss of genetic diversity can be extremely rapid. As breeders seek to produce animals that are more uniform as they are selecting for type, the resulting homozygosity makes the population more vulnerable. At the extreme, all individuals in the population would become genetically identical. Then of course, breeders would have no differences between animals to select for, and a novel pathogen could exterminate an entire breed.
The two basic goals of genetic management are to control the loss of genetic resources from a population, and to use breeding strategies that maintain a healthy population of animals that meets the needs of the breeders. The principles are the same for dogs as they are for cheetahs, horses, chickens, fish, or even plants. Fortunately, excellent tools have been developed over the last 20 years by population and conservation geneticists that have revolutionized the breeding of domestic animals including dogs.
POPULATION GENETICS
Genetic management requires the ability to understand how the frequency and distribution of genes in a population change over time. In fact, the field of population genetics was developed by biologists trying to understand the processes of evolution and adaptation, and it has since been put to good use by conservation geneticists and animal breeders in the management of captive populations.
The changes in the traits of a dog breed over time are also a form of evolution - through reproduction and selection (both controlled by the breeder), some alleles become more frequent in the breed and some become less frequent or are even eliminated. If we have some basic information about the population of interest - the number of individuals, sex ratio, how often they breed, the number of offspring they have, how long they live, and so on - we can predict how the frequencies of alleles will change from one generation to the next using statistics and probability. As you read about population genetics you will run into lots of complicated looking equations. Our computers do all the math for us now, and you only need to understand what they mean and how they work in general.
