More on Genetic Diversity

What is “Genetic Diversity”?

Genetic diversity is a term that is thrown around and not often well understood.  Is it natural?  What happens in wild populations when genetic diversity is lost due to hunting, illness, or habitat loss etc?  Believe it or not, measuring genetic diversity is one way conservationists can rank certain species as threatened or endangered.  Loss of genetic diversity creates a population ill equipped to handle illness, changes to the environment, or shrinking habitats.  It also can create a misalignment of the immune system and dysfunction in reproduction.  Even if numbers remain high in a species, loss of diversity can affect them negatively.

So how does this apply to dog breeds?

As a species, canines have a lot of genetic diversity.  However, we segregate our species by breed.  Many breeds in general have large numbers (although not all!), but we also often apply selection pressures to (make breeding choices for) them that result in the loss of genetic diversity.  These pressures include popular sires, world wars, selection for type etc.  While these pressures create our idyllic breeds, they also reduce our genetic diversity at the breedwide level and can fix breed specific diseases.  The further down the path of genetic diversity loss we travel, the greater these effects, regardless of the number maintained in our breed.

So when we talk about diversity in dogs, what are we talking about?

In general when people talk about diversity, they are talking about two aspects: diversity within a single dog and diversity within the breed itself.

When we talk about diversity within the dog, we are assessing how much of the genetic material they inherited from their sire is exactly the same as the genetic material they inherited from their dam.  When a dog inherits too many of the same genes from both parents, we call them inbred.  It’s well known that inbreeding can cause many issues in populations and therefore it is encouraged to breed for heterozygous, or outbred, dogs. Inbred dogs also are more likely to express any hidden recessive component diseases and be affected by the disease.

What does diversity at the breedwide level mean?

Diversity in the breed means that the breed as a whole has lots of different genes.  The genes can be so simple as coat color, to as complicated as the immune system or cardiac structure.  When the genes begin to be depleted, often genes that code for illness then become more frequent.  When this happens, those genetic flaws will be expressed more often. This is often referred to as biodiversity or allelic richness.

Is this a silver bullet for disease?

All dogs will have some mutation in their genome.  The reason genetic diversity is desirable is that it dilutes the risk of disease by having more genetic variety within the dog and within the breed as a whole.  As dogs within a breed become closer related genetically, the greater the risk is of expressing disease.

Now what does that mean for your breed?  Some breeds are in good shape, they have lots of diversity remaining.  Some of those breeds have a lot of diversity, but the majority of the dogs within the breed are bottlenecked on a few very specific genetics, with the majority of the different genetics retained in only a few individuals.  Other breeds have lost a lot of their genetic diversity and have a severe genetic bottleneck. No matter the situation, all breeds should strive to maintain what they have so they do not get in a worse situation or get to the point of needing to bring in new genetics. We are the safeguards of our breeds’ futures.