It's a pretty lengthy journey, so be warned, but most of it is worthwhile and interesting. I think I already mentioned about the researcher who severed the tails of more than thousand mice to see if their progeny would be born tailless. It sounds ridiculous, but was a crucial experiment testing a contemporary hypothesis of how inheritance works -- that 'information' from all parts of the body travelled to the gonads to inform the sex cells of how those parts were organized.
Darker chapters go into the Holocaust and the US Supreme Court case leading to the sterilization of Carrie Buck. It was not only a perversion of science, but actually not even based on facts. Despite the cry of 'Three generations of imbeciles are enough,' there's little evidence to suggest Buck or her daughter were imbeciles. Both were average students, and Buck was probably hidden away as feebleminded and promiscuous for having been raped by the nephew of her foster parents.
One of the interesting distinctions Mukherjee makes is the difference between heritability and inheritability. Heritability measures the extent to which variations in people are due to genetic (as opposed to environmental) effects. Through studies with identical twins raised separately and other means, it's clear that homosexuality, intelligence or schizophrenia are heritable traits. There is a genetic link of a greater or lesser extent. But unlike something simple like eye color, these traits are not inheritable -- easily passed from parent to offspring. These traits are a result of complex interactions of multiple genes. Having such a trait is a complex result of having gotten many genes from both your mother and father, and how they mix together. When you pass on genes to your offspring, only half of your mix goes into the batter, while your partner provides the other half. If we flip metaphors to cards, if you get dealt the full house of the trait, you pass three random cards to your kid, and your partner does the same with his full house, and the kid winds up with a pair of sevens with an ace kicker. Oh well.
Mukherjee is a Rhodes Scholar with a double-barreled MD with a PhD in biology, but the book is written at a good interested layman level.