What is genetic diversity?

*Do not copy or distribute these texts without the approval of Coen Huisman or Linda van Andel*

In the past couple of years, dog breeding has had a lot of bad press. Almost everyone that is involved with dogs in The Netherlands, has seen the episode of Radar (Dutch consumer television program) about unhealthy breeds and hereditary diseases in breeds (link). This subject really drew the attention after the English documentary from 2008, named “Pedigree dogs exposed“. A lot of dog breeds have unhealthy breed characteristics, many hereditary diseases and high inbreeding percentages. Besides this, in the past years there have been many law suits against breeders about breeding unhealthy dogs. Luckily the Icelandic Sheepdog doesn’t have a lot of hereditary diseases or unhealthy breed characteristics. But still it is also important for us, breeders, to keep it that way and we need to keep a close eye on our breeding policies in this respect. 

As breeders, we often breed to maintain our breed and ideally improve it with regards to exterior, behaviour and working ability. In order to maintain the breed, breeders are very much aware that they cannot do this without looking at the health of the dogs. Genetic diversity is extremely important when it comes to the health of a breed, but it has been virtually impossible to take this into consideration before, simply because the information wasn’t there.

Genetic diversity within a closed population is never more diverse than the diversity of the founders of the breed. The founders are the dogs that all offspring derives from. Because the diversity within a breed can never be more than that of these unique founders, it’s better to start a breed with for example a 100 founders than 20.

With a 100 founders you breed with the unique genes of 100 individuals, with 20 you only have the unique genes of 20 for your breed. When procreating, you always get half of the genes of the father and the other half of the mother. In a closed population (as we have with purebred dogs and endangered animal species), there is only a limited amount of genes. This lack of new genes restricts us regarding the diversity within the population, and it is therefore extremely important to maintain diversity as much as possible.
Unfortunately within dog breeds often only 1 in every 10 pups is used for the next generation. For the Icelandic Sheepdog, the average litter size is 5 pups per litter. Every pup gets half of his genes from the mother and half of the father. So in every generation we lose genes in dog populations, because we do not use as many animals as possible for the next generation. The image on the right illustrates this perfectly.
In the first generation there are many different dogs with different genes, but because there is only a limited amount of genes that is passed on, you increasingly lose more unique genes.

What you want, is that every dog in the population contributes to the next generation. And that this way, you will have dogs with many unique and different genes in them. In the image below you can see that as many as possible different combinations have been made with a few unique dogs, so that each dog provides an equal contribution to the next generation and all genes have been passed on. This is the perfect picture.

When we talk about genetic diversity, it’s important to also discuss inbreeding and kinship. When calculating the genetic diversity, we use kinship. The more genetic diversity within a breed, the lesser the animals are related to each other. The less animals are related to each other, the lower the inbreeding percentage. It’s important to realise that inbreeding isn’t necessarily the cause of little diversity. It is true that a lack of genetic diversity causes a rise in inbreeding though.

When you want to calculate the real inbreeding percentage within a combination, you can only do this when taking all generations into account, as calculations over 5, 6 or 7 generations will have a totally different outcome. This is because these calculations didn’t go all the way back to the founders. The inbreeding of generations back to the founders will have to be added to the generations that follow. Also, in generations that follow, you will have many problems with popular males that have been used a lot (the so called matadors).

This is also the case with the Icelandic Sheepdog, where some males have had over 50 offspring. This makes the inbreeding in our population very high and the diversity low.

Lack of genetic diversity has a big impact on a population. The first consequence is the augmentation of genetic diseases. Another consequence is ‘inbreeding depression’  and is, in my opinion, the worst that can happen to your breed. Inbreeding depression:

  • lowers the ‘fitness’ of the animals; they have a shorter life span and produce less offspring. Also, fertility decreases. With cattle breeding, this aspect has the utmost attention, while for instance cows have a lower milk production because of decreased fitness.
  • causes immune system defects, which in turn results in external diseases, like bacteria and viruses. Next to this, the chance of cancer increases.

Next to these consequences of a lack of diversity, it is also a fact that without diversity, you can never improve your breed anymore. Without diversity, you will keep the same dogs, generation after generation. When you need more feisty dogs to improve the working abilities of a breed, they might not be there anymore. Or if you want to improve tail carriage, there is no possibility to do so. With a lack of diversity, you are also not able to adapt your breed to its surroundings, or the wishes and desires for breeding or the breeding standard. 

We can be brief when discussing the benefits of genetic diversity. Genetic diversity prevents all the negative aspects, such as the higher chances of hereditary diseases and inbreeding depression. Next to that, diversity also makes it possible to improve our breed faster and by being able to select, we can achieve our breeding goals. When I use the word ‘selection’, I do not mean ‘exclude’ as we often see with dog breeds. 

Luckily there are ways to improve genetic diversity. This is mainly done by:

  • restricting the problem of overly used dogs, i.e. put a restriction on the number of litters a male or female can have.
  • restoring the balance by prioritising dogs from unique lines, in order to bring more balance to their share of genes in the population in relation to the more popular lines. 
  • promoting more one-time parent litters. For the breed it would be better when more dogs are used for the next generation, and to only produce 1 litter.


What we use to get a better overview within our population about the dogs that derive from important lines and that can improve our diversity, is ‘mean kinship’. For more information about mean kinship, visit this page.

*Do not copy or distribute this text without the approval of Coen Huisman or Linda van Andel*