Matt Ridley's Genome: The Autobiography of a Species in 23 Chapters is a good introduction to human genetic structure. For each chromosome, Ridley selects some feature as the starting point for a chapter about human DNA. Though that's a bit of gimmick, it's a clever way to organize a book.

For example, chromosome 4 includes the gene that determines whether you'll get Huntington's disease. Ridley discusses the disease, its history, and the genetic markers that distinguish people who will be stricken with Huntington's from those who won't. He then explores the ethical and psychological question of whether people should be tested to determine whether they'll get Huntington's disease, which has no cure.

Ridley covers a wide range of topics. A majority of them deal with variations in the genetic code between different individuals, and the ways in which those variations change people's traits and health. Ridley also discusses the structure of the genome, genetic similarities and differences across multiple species, genetic engineering, junk DNA, and other things.

One surprise was the extent to which behavior is determined by ones genes, instead of the environment. For example, children of physically abusive parents are more likely to become abusive as adults. Genes, not childhood conditioning, cause that correlation. Abused stepchildren don't tend to become abusive, while adopted children of abusive biological parents do.

Genome covers lots of interesting material that I hadn't seen before. For example, evolutionary competition exists between individual genes, within a single creature, to determine which genes are propagated to future generations. That competition explains, for reasons I won't go into, why the Y sex chromosome is so small.

Overall, I'd strongly recommend this book.