Genetic Diversity 101

Genetic diversity is the variation in genes that exist between individuals within a population. Each variation of a gene is called an allele, and when a population has many different alleles for the same gene it is indicative of a high amount of genetic variation. Conversely, having less allelic variation in the overall population is linked to higher incidences of diseases and is usually indicative of an inbred population.

For an individual dog, each gene location (locus) can have two alleles: one from each parent. If they are the same this is called homozygous; if they are different this is called heterozygous. Whether an individual dog has more or less homozygous alleles is a general indication of how inbred it is, but it is also worth comparing the individual to its population. For example, there may be a dog that is very inbred on rare lines, so has very different alleles than the majority of the population even though the dog in question is quite homozygous.

Breeding for Diversity

Most people think of genetics in terms of pedigree averages. Because each individual gets 50% of their genetic material from each parent, it is extrapolated that this even splitting of genes from progenitors continues in each subsequent generation. That is, it is assumed that a grandchild retains 25% of the genes from each grandparent, or that a great-grandchild retains 12.5% of the genes from each great-grandparent, and so on. The reality is instead that each parent could have passed down anywhere from 0-50% of each of its parents' genetic material. So it is possible that the grandchild gets 0% of their genetic material from the maternal grandmother, 50% of from their maternal grandfather, 15% from their paternal grandmother, and 35% from their paternal grandfather. Or perhaps the split is more even: 24%/26% and 20%/30% from their maternal and paternal grandparents respectively.

It is easy to lose genetic diversity over time despite assuming from a dog's pedigree that it should be quite outbred. Breeding for diversity must consider individuals' actual genetic makeup, not just pedigree averages, in order to maximize the number of alleles present in (and their distribution within) the overall population. This information can be measured in many ways; the Doberman Preservation Project uses the metrics reported by the genetic diversity test panel from UC Davis' Veterinary Genetics Lab.

inheritance variation illustration (source)

Most people think of genetics in terms of pedigree averages. Because each individual gets 50% of their genetic material from each parent, it is extrapolated that this even splitting of genes from progenitors continues in each subsequent generation. That is, it is assumed that a grandchild retains 25% of the genes from each grandparent, or that a great-grandchild retains 12.5% of the genes from each great-grandparent, and so on. The reality is instead that each parent could have passed down anywhere from 0-50% of each of its parents' genetic material. So it is possible that the grandchild gets 0% of their genetic material from the maternal grandmother, 50% of from their maternal grandfather, 15% from their paternal grandmother, and 35% from their paternal grandfather. Or perhaps the split is more even: 24%/26% and 20%/30% from their maternal and paternal grandparents respectively.

inheritance variation illustration (source)

It is easy to lose genetic diversity over time despite assuming from a dog's pedigree that it should be quite outbred. Breeding for diversity must consider individuals' actual genetic makeup, not just pedigree averages, in order to maximize the number of alleles present in (and their distribution within) the overall population. This information can be measured in many ways; the Doberman Preservation Project uses the metrics reported by the genetic diversity test panel from UC Davis' Veterinary Genetics Lab.

Genetics of Outcrossing

Registered dog breeds with closed stud books have closed gene pools. With careful breeding the available genetic diversity may be preserved or better distributed, but it cannot be increased. Outcrossing, or breeding to an individual of a different breed, is the only way to introduce additional allele variations to those present in the original gene pool. However, as already mentioned above, it is easy to lose introduced genetic diversity over subsequent backcross generations, or repeated breedings back to members of the original breed. So in order to guarantee a sustained increase in genetic diversity over time, outcrossing must occur repeatedly and continuously.