I think the more information you have the more accurate you can get. In the case of Chelsea there only was DNA available. Personally I find this stuff to just be very interesting. While some people are skeptical I just find this to be an intersection of art and science. In the Probably Chelsea exhibit they explain that the ones picked to show the media were of the higher percentages. However since Chelsea was open to it there was more they could depict based of her DNA. It's a pretty powerful exhibit to see because some of the possibilities look nothing like Chelsea. A person with that face would be identified as a completely different race as Chelsea. To me it empathized how much the concept of race is really a social response to the expression of a person's DNA. The idea that we could look like basically anybody else is really powerful.

It's a side tangent but if you are In San Francisco I recommend checking out the Exploratorium. It's a really fun and thought provoking science museum.