If a human were cursed with the need to transform into a specific animal (i.e. a canine), would his DNA change after the transformation?
I would appreciate help in answering this question. This is for research on a book I am in the process of writing.
Ignoring the physical/mechanical issues with the transformation itself (a wizard did it), I see another possibility for the DNA: a mixture between the two.
Point one: The genomes of different species are mostly identical. See some numbers with sources here. I'd estimate that a human and werewolf dog share between 80 and 90% of the their genome, so it wouldn't be too much of a stretch for an individual to have all of the genes necessary for two species.
Point two: Only a small fraction of our genome contains actual coding sequences, most of it is "junk." Even out of our genes themselves, not all of them are "active" at any one time. The relatively new study of epigenetics studys what causes genes to be activated and deactivated, and what influences the 'strength' of their expression.
Putting these two together, you might say that the genetic structure of your individual has been modified to contain all the genes from both species, and some epigenetic mechanism 'switches' between the two sets of genes that are specific to one or the other species.
That depends, what do you mean by transforming into a canine, and how does the process work?
Fundamentally, humans aren't capable of transforming into other animals. Either some external influence is transforming the human into a canine, or else they are some human-like (but decidedly non-human) creature with the innate ability to transform.
In the former case, probably. On a basic level, if the DNA of the organism isn't canine DNA, then it's still some other creature. If the internal organs/form/etc. are all canine, then the DNA will at least need to encode the proper growth patterns for the cells in order to stay alive. Cells are constantly dieing and new cells created, and without the proper DNA, this process won't work.
If the creature is a natural shape-shifter, then it probably has shape-shifter DNA. Canine DNA is incapable of this, so it will need some non-canine DNA if it is to go about the process of changing shape. It may create some canine DNA in addition to its shape shifter DNA, or at least canine-like DNA, but will remain fundamentally a shape-shifter and not a canine.
It would be his own DNA that gave him the attribute of being able to change into a canine. He would not be a human being, he would be a different species, supposedly descended not from when we split the primates up, but it would have to be way, way back, potentially as far back as Boreoeutheria splits.
Unless you wanted to add in some fantasy mad-scientist thing, where his DNA was somehow created artificially: in which case, this answer still stands: he has his own, unique DNA.
EDIT - More answer, to try to meet the intention of the story:
Further, no - If someone's DNA was altered so drastically (and it would be instantaneous, as cells are constantly dividing), it would not mean that they would have a fast transformation.
Suddenly cells are behaving differently, and there are missing cells as well that you need to create. Muscle would start growing in awkward places (breaking out bones), organ failure as they start and stop growing in areas: it would be an ugly and horrific death. Please just have one DNA for the sake of your characters.
Does it transform DNA? Sure. Why not. Its your book, you can really do anything you want to. It doesn't matter if it makes sense or not.
If you're looking into science based ways to do transformation, you can make educated decisions as to whether the DNA transforms or not, but it's really up to you.
DNA is what we build proteins from. We upregulate genes, and it causes us to make proteins that we use to manage our cellular lives. That's its entire job. Nothing more. Whether DNA is changed or not depends on how you want to have your transformation process to work.
You could make an argument that the DNA is changed to be more canine, then something kicks the cells into hyper-super-ohmygod-howtheheckisthispossible overddrive and instead of producing a reasonable amount of proteins per hour, they produce some ungodly high rate (multiple orders of magnitude faster than normal) to give you the raw materials to make a transformation occur. To have this process work, you'd have to alter the DNA.
On the other hand, with the amount of handwaving it takes to admit a science based human/animal transformation, you could also claim that this transformation occurs purely in the proteome (the collection of protiens in the body). This is just as scientifically reasonable as doing it with DNA, give or take, so there's no particular reason DNA has to get involved.
It all comes down to what you believe you can convince your readers is acceptable. Work done in the genome (DNA) has far stricter rules than work done in the proteome (proteins) which is actually still a relatively unexplored territory for science. If your readers want strict rules, DNA based transformation may make sense. If your readers don't care about the rules, but care about who kills whom and who hooks up with whom, trying to make a DNA based transformation process might get in the way of telling your story.
In the end, trying to explain how major physical changes (i.e. vampire teeth or werewolf musculature) occurs is substantially more important than whether a particular genome sequence is altered. Those changes are completely unexplained by either changes in the genome or proteome. Whatever reason you have for those changes to occur will completely dwarf any molecular level decisions you choose to associate with the transformation. You may choose to incorporate genome or proteome rationales for some of the changes, but 99.9999% of the changes are well beyond science's perception of what cellular mechanics of proteins and DNA are capable of achieving. Don't sweat the small stuff: choose DNA or no-DNA purely based on whatever makes your plot the simplest to tell, and never look back.
Remember Sanderson's first rule of magic: The authors ability to resolve conflict with magic is directly proportional to the readers understanding of it. As long as the understand what magic can and cannot do, it doesn't matter what technical approaches you assign to any particular magical ability.
