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Why is KK lethal for wolves?

Posted: Wed Jun 24, 2020 12:05 pm
by GoldenBeauty
How come the KK gene in wolves produces sick pups or is even lethal? Why isn't this the same thing with dogs who will always produce healthy puppies even if bred Kk x Kk?

Re: Why is KK lethal for wolves?

Posted: Sat Jun 27, 2020 3:04 pm
by DaniBeez
GoldenBeauty wrote:
Wed Jun 24, 2020 12:05 pm
How come the KK gene in wolves produces sick pups or is even lethal?
Hey GoldenBeauty,

In real-life grey wolves, the KK genotype does not automatically produce sick pups or cause lethality in utero (in the womb). At least, I still cannot find direct evidence or statements for either of those things, so I assume they have been inferred from the observations of less reproductive success and shorter lifespans in some KK wolves. KK wolves can still grow up and have pups, but they typically aren't as successful at these milestones as Kk black wolves or kk grey wolves. Here's what we know:

Scientists noticed in Yellowstone that between 1996 and 2014, about 45% of the wolves had black coats. This percentage stayed constant for 19 years, over about four generations. This led them to ask why the proportion of black coated wolves has stayed like that over time. They then found evidence that there could be advantages to having a black coat. They observed higher annual survival, lifespan, and lifetime reproductive success in some of the black wolves.

Key word 'some', because these advantages applied more to the black wolves with the heterozygous condition, Kk. On average, KKs weren't living as long, or having as many pups as Kks or kks (grey/agouti). Again scientists wondered why this was the case.

Since Kk wolves were typically doing better than the KK ones, scientists realized that the black coat color, which is visually indistinguishable between the two genotypes, wasn't the reason for the advantages. It wasn't a camouflage advantage. There was something else going on.

The reasons are on the cellular level. The K locus encodes a Beta defensin protein. In mammalian cells, a defensin protein's job is to disrupt the contents of foreign invading cells, such as from bacteria. In other words, they help an animal's immune system fight disease.

As to why being Kk is more advantageous than KK in wolves? I don't think it is known at this time. Being KK at this locus must have negative implications on the cellular level, compared to being Kk or kk, which translate to subtle disadvantages for the animal when it comes to survival and reproduction activities. It could be a complex pathway that isn't completely understood at this time.

Why isn't this the same thing with dogs who will always produce healthy puppies even if bred Kk x Kk?
Now that we've established that homozygous black wolves can still survive and reproduce, the contrast between them and domestic dogs isn't as stark.

As well, there are other genes controlling color, and they too may or may not have implications for survival and reproduction. We can also consider that domestic dogs get a lot of help from humans in both of these areas, and aren't as likely to encounter dangerous situations or the same diseases as their wild relatives.

Hope that helps! Can provide the sources if needed.

Re: Why is KK lethal for wolves?

Posted: Mon Jun 29, 2020 6:48 am
by GoldenBeauty
So basically the K gene controls the coat color but it could also effect other genes? Maybe it could control the immunity? I always found it odd how some black breeds (like Belgian shepherds for example) always had the KK gene but it never really seemed to effect them. Maybe it's because of dogs living a domestic life etc. Maybe domestication has altered the way genes behave.

Re: Why is KK lethal for wolves?

Posted: Mon Jun 29, 2020 1:59 pm
by DaniBeez
Yeah. The K locus has the DNA/genetic code for creating the Beta-defensin 103 protein. This defensin protein has a "side role" in influencing pigmentation because it binds to another protein--a melanocortin receptor--that is found in melanocyte cells. Melanocytes are special cells in mammalian skin. Melanocytes produce melanin, the pigment responsible for the black color of skin and hair/fur. So having one or two "big K" alleles at your K locus means the defensin proteins from this locus will bind to melanocyte cells and produce more melanin pigment than if you were kk, or "grey".

But like in dogs, coat color has genes other than K contributing to its expression. As well, traits like "immunity" and "intelligence" are also complex traits, which means that many genes are working at the same time control the overall expression of the trait. As well, an organism's environment also can affect how a gene pathway is expressed.

Domestication definitely influenced gene expression too. When our ancestors first started domesticating animals by encouraging the mating of certain animals that had characteristics they liked, they didn't realize that they were also changing the underlying genetics of the animals too. That understanding came later on in history, and we are still learning how these genetic pathways work today. We might think pugs are "cute" for example, but many unintended health problems came with their unique look. Genes affect other genes and traits in complex pathways!

We may never fully understand these pathways either in our lifetimes, but as the cost of whole genome (genome = the whole entire genetic code) sequencing becomes exponentially cheaper (about $1000 today, whereas twenty years ago it was a hundred million per genome), we will uncover more relationships between gene expression patterns and the expression of traits we observe, like coat color.

So yeah, perhaps the reason that the K locus doesn't seem to have as much of an observable impact on domestic dogs is because other genes are masking or overriding any negative effects of being homozygous black (KK), as well as dramatic differences in lifestyle.