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I have edited the question, and it is no longer too broad. My one and only question is the one shown in bold below. If you agree that it is not too beoad in this state, a vote to reopen would be much appreciated.

Imagine that, somewhere, people start breeding seals for as companions, in the same way we did with dogs. I know that there are dog breeds for hunting, herding, fighting and others, but nowadays most people just get dogs for the fun of it.

Anyway, this civilization lives largely on a vast coastal network of waterways like this, except with more solid ground:

enter image description here

In this environment, water not only exists as an ocean, lake or river, but winds everywhere through cities and towns, so that, in some regions, you would rarely be further than 100m from a body of water.

Since large areas of water are readily accessible here and seals are relatively common, they took the place of dogs in our society.

However, this was millenia before the time I have in mind now, and by now seals have been bred into a myriad of breeds for every conceivable purpose.

enter image description here

The ancestral species of seal is the harbour seal, Phoca vitulina (shown above). What I want to know is, after thousands of years of selective breeding, what would othe domestic seals look like?

That is the only question I am asking currently. This question encompasses morphological, pelage and other kinds of visual aspects. I know that the appearance of a domestic animals depends on what it was bred for, and these seals have breeds for fishing, aesthetic appeal, swimming ability, fetching sunken objects and personal protection while at sea.

I know this may seem broad, but what I mean is: After breeding for those specific purposes, what changes might the seals experience and would there be any genetic obstacles to them achieving this?

If you have any critique, complaints or suggestions for this question, please do say so, and I will amend it promptly.

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closed as too broad by John, Ash, L.Dutch, ShadoCat, Mołot May 23 '18 at 22:36

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ They'd have dogs that preferred water to land, if you breed something to fill the niche currently labelled "dog" you'll get dogs, in as many varieties and with as many weird mutations as you want to include. $\endgroup$ – Ash May 23 '18 at 18:13
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    $\begingroup$ you asked about half a dozen questions, pick one. $\endgroup$ – John May 23 '18 at 18:16
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    $\begingroup$ The main question is "What would the domesticated seals look like?" This can be clarified by splitting it into a few categories, which I did. At the end, I brought up a couple of foreseeable impediments to the domestication. $\endgroup$ – SealBoi May 23 '18 at 18:35
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    $\begingroup$ As @John has aluded this question is too broad, it also falls into Why is my question "Too Story Based and how do I get it opened? territory as well. $\endgroup$ – Ash May 23 '18 at 18:46
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    $\begingroup$ Just a note, "too broad" doesn't necessarily mean you're asking multiple questions (though that's a simple case). It could also mean that the one question you're asking is looking to cover too much terrain. For example, an archetypical "too broad" single question might ask us what would be the consequences of a single widely influential historical person never having lived, or having been killed by something at a very young age. Such a question would be too broad not necessarily by virtue of asking too many questions, but asking for too many consequences of the one change being asked about. $\endgroup$ – a CVn May 24 '18 at 11:37
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Breeding of animals can result in changes that are both intentional and unintentional. Intentional changes are pretty straightforward. If you breed for a long-haired seal, you’ll get a long-haired seal. Presumably you are looking for information about how unintentional changes can occur as a result of breeding for other traits. This will happen and there are two primary mechanisms by which it will occur.

The first is that by selecting for certain traits you will also be selecting for unrelated traits controlled by the same genes. This is called Pleiotropy. Many genes play multiple roles in an organism in different places and at different times in the body. Additionally, due to the complex nature of living systems changing one thing can often affect other seemingly unrelated things. An example would be that in the process of breeding for friendliness you might also breed for lower intelligence as perhaps those things might be correlated in the seal. In this way some related and potentially unrelated traits will be found with increased frequency in your domesticated seals.

The second mechanism is that selecting for certain traits also effectively selects for traits encoded by nearby genes. This is because when we inherit genes they aren’t all randomly shuffled. There is a genetic linkage between genes near to each other on the same chromosome. Seals who inherit the gene you are selecting for are also more likely to inherit nearby genes on the same chromosome. So, if one of the genes for friendliness happens to be next to a gene for Tyrosinase and by chance the most friendly version of the gene happens to be linked with a non-functional version of Tyrosinase then breeding for friendliness will also breed for albino seals. Depending on just how strong the linkage is between these two genes you will get some proportion of crossovers that separate them and so could breed a seal that was not albino if you so desired. But the concept remains that by random chance some completely unrelated traits will be linked with the traits you are trying to breed for and so will show up in your domesticated seals.

So the answer to your question is that we can’t predict any specific phenotypic traits that will change in response to domestication, but we can predict that almost certainly some phenotypic traits will change.

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They would definitely take on some morphological changes. After thousands of years of breeding that is inevitable.

You asked about the attempt to domesticate Foxes. Although the foxes in that attempt had unpredictable coat colors, that attempt to domesticate was not active nearly as long as "thousands of years". A chaotic gene expression would certainly be smoothed out and predictable after thousands of years of breeding.

On a meta level: What is the purpose to making your story so accurate in this way? Nobody except a few experts has memorized knowledge about the specifics of Seal genetics. You can really do whatever you'd like with seal genetics and no one except those few experts will have their immersion broken. If you want to have problems with the genetics in your story, that's fine. If not, that's fine too.

I should also mention that Harbor Seals are not very agile on land. They could be bred to have better land mobility, but there is an alternative critter that is already well adapted to both land and water: The Sea Lion enter image description here

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    $\begingroup$ I'd also like to add that I really like this idea. People are always saying that seals are dogs of the sea. It's really cool to see you fleshing out that idea. Given your terrain, it seems surprisingly plausible too! Water boyes :) $\endgroup$ – Jared K May 23 '18 at 19:00
  • $\begingroup$ Thank you! To be honest, I'm almost asking this question out of curiosity as well as for my world building. Also, I feel more comfortable in the knowledge that my fictional pets are designed with purpose and believability. I think that by doing that, the story can feel more realistic to viewers. $\endgroup$ – SealBoi May 23 '18 at 19:17

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