It's a pretty common staple of fiction to have characters change gender or transform using DNA-based magic. Sometimes it's called science, but it's always magic. Books like Animorphs, comics like El Goonish Shive, a bunch of anime all revolve around transforming characters. El Goonish Shive is the best example and my favorite, because author Dan Shive describes the mechanics of it in minute detail. Whether this is to fend off Nerd Criticism or simply love of describing it is unclear, but it gets me thinking. Lots of things get me thinking. Of course, my thoughts on the matter might not be as smart as I think; I'm not a biologist and my understanding of genetics is mostly limited to National Geographics articles I've skimmed, a couple of bio lectures in college, and the very material I'm discussing here.
Generally in these pieces of fiction, a character will imitate someone's DNA and they'll produce a mirror-image clone; the original and the copy look identical. Animorphs was pretty unique in its recognition that DNA does not store physical injuries and as such a DNA clone would not share any scarring or injured limbs. That means that a magically generated copy made purely from DNA would not share any injuries the original has. On the surface, that means obvious things aren't imitated; tattoos, the various nicks and scars people go through life getting... but there are other things. Some are definitely going to be noticeable in the correct context, others I'm less sure about. Most American men are circumcised, to start, so a completely genetic copy of a man would have an easily identifiable turtle neck. Belly buttons are another example: the size, shape, even presence of the belly button isn't defined genetically.
DNA is not a blueprint for the body, only it does not have a lot of power to specify the materials used. Nutrition vastly impacts the way your body is built from DNA. Malnutrition can and often does have a permanent effect on the way your body looks--someone who did not have enough calcium growing up is going to have different bone structure than someone who had enough. Muscle and fat aren't genetic, either. In the last year my weight has fluctuated about fifteen pounds in either direction of 170. On any given week my weight changes by five pounds depending on how recently I've been to the gym.
Generally in these pieces of fiction, a character will imitate someone's DNA and they'll produce a mirror-image clone; the original and the copy look identical. Animorphs was pretty unique in its recognition that DNA does not store physical injuries and as such a DNA clone would not share any scarring or injured limbs. That means that a magically generated copy made purely from DNA would not share any injuries the original has. On the surface, that means obvious things aren't imitated; tattoos, the various nicks and scars people go through life getting... but there are other things. Some are definitely going to be noticeable in the correct context, others I'm less sure about. Most American men are circumcised, to start, so a completely genetic copy of a man would have an easily identifiable turtle neck. Belly buttons are another example: the size, shape, even presence of the belly button isn't defined genetically.
DNA is not a blueprint for the body, only it does not have a lot of power to specify the materials used. Nutrition vastly impacts the way your body is built from DNA. Malnutrition can and often does have a permanent effect on the way your body looks--someone who did not have enough calcium growing up is going to have different bone structure than someone who had enough. Muscle and fat aren't genetic, either. In the last year my weight has fluctuated about fifteen pounds in either direction of 170. On any given week my weight changes by five pounds depending on how recently I've been to the gym.