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In light of the current US supreme court case, I'm curious if enough information can be teased out of a DNA sample to get a "reasonable" approximation of the suspect (never mind the legality). I realize the term reasonable is subjective, so characteristics, such as skin color, hair color/texture, approx height, eye color, freckles, etc. I came across this article a few years ago, but the company that made the test went bust in 2009. It could detect race (how accurately?). I seem to recall reading an article a few years ago stating that "soon" we'd be able to get an approximation of appearance from a DNA sample that was better than a sketch artist could provide, though I can't recall now where I read it.

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In theory it's possible to have an approximation, but not to know with certainty. Identical twins have the same genomes and look very much alike. Whether it can be done in practice depends on how well we can model the relationship between genes and looks and on how much information is necessary for a judge to permit arresting and questioning a suspect.

Scientists know relatively little about how genes influence physical appearance yet. The height of the suspect is controlled by hundreds of genes with complicated interplay between them, so I don't think it's possible to estimate it just yet. Eye color is more simple: it's controlled by only 3 genes. We know weight is partially controlled by genetics but exactly which genes are responsible is not clear. Age is impossible to tell by DNA alone. Skin color should be predictable, since it's caused by melanin production, and we know which genes are responsible.

So to sum up, DNA analysis can tell the gender, skin color, and eye color of the suspect, but very little about height and weight, and virtually nothing about age. That's not enough information to identify a suspect, although perhaps someone with legal knowledge could comment on this.

But let's say in the future we know enough to determine all these traits. Then DNA analysis would be helpful but never enough to identify a suspect. The problem is that different cells in your body undergo different mutations in their DNA with time. That's how one gets cancer. Let's say there's a mutation in the eye color gene in skill cells from a murderer found on a victim's body. It won't affect the murderer's eye color but it will affect the forensic analysis. So it's impossible to know for sure what the suspect's appearance will be.

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I agree with most of your assessment. I'd think that some genetic markers could give an approximation on traits like height though. Clearly diet makes a difference too, but working under certain assumptions I'd think a rough estimate could be made. Fair point about mutations, but I'd be curious to see just how significant those turn out to be on the whole. There would clearly need to be all kinds of other traits analyzed as well. Things like cheek structure, lips, nose, hair texture, freckles, widow's peak, etc, etc. Some of these would be easier to glean than others... –  single_digit Mar 19 '13 at 19:59
@single_digit You're right to point out that one can make a rough estimate, and perhaps it will get more accurate in the future. One of my main points was actually that a judge would not consider the information enough at present to issue a search or arrest warrant, for example, so it's unlikely that these methods would help in an investigation. I have no formal legal knowledge or experience, though. I'm curious for feedback on this from someone who knows more about the law. –  Drosophila Mar 19 '13 at 21:11
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