How much can you tell just from someone's genes?
Here's a thought experiment. Suppose you could copy and recreate a person's genome pretty much exactly, give or take a few mutational errors. You could implant this genome-copy into an egg cell, bring the resulting foetus to term and allow it to grow into a full adult. How similar would the copy-person be to the original?
Of course, this is not a thought experiment. I'm simply describing the case of twins separated at birth. And how alike are these twins? Well, in appearance, personality, health and intelligence they are as alike as ... twins.
If we understood the human genome in all its SNP and copy-number variants, we wouldn't need to recreate a human copy, we would simply read off the attributes of the person with that genome. Police profilers can already do this for many traits (I mentioned recently facial reconstruction from DNA samples). In the future we will be able to know and do much, much more.
It's simplest if you donate a sample of your DNA to a gene-sequencing company. My mother and myself have sent our saliva kits to 23andMe (here's my report) and even with the restricted coverage currently offered there's lots to learn.
My father died in 2009, before the age of consumer genomics. If we had his DNA we would know quite a lot about his health and personal traits right now; and of course in the future we would know so much more. Personality, health and intelligence would be my interests.
Forensic techniques get better all the time. We have some of his clothing and other personal possessions; there must be traces of his DNA. If we wait a while till the prices come down, I think there is an excellent chance we will be able to find samples of his DNA and sequence them. Our family genetic history will take a further step forwards.
I wrote a little piece for sciencefiction.com about this a while back.