HeredityIntroduction
It is the naming ceremony of Riya's baby cousin, and everyone in the family has an opinion. "She has her father's ears!" says Dadi. "No, those are her mother's eyes," says Bua. Riya's uncle, who grows sugarcane near Kolhapur, just laughs: "In my field nobody argues. Every plant looks exactly like the next one."
Both of them are right. In the last chapter you saw that reproduction makes new individuals that are similar to their parents, but subtly different. Some variation creeps in even when a single parent reproduces on its own, and sexual reproduction makes the most of it. A sugarcane field is grown from pieces of stem, so its plants differ very little; in a human family, where every child has two parents, the differences are easy to see.
Sort these groups into two buckets: groups whose members are almost alike, and groups whose members are clearly different from one another.
Look at what each bucket has in common. Everything that is almost alike came from one parent — a stem piece, a cutting, a dividing cell. Everything that is clearly different came from two parents, through sexual reproduction.
In this chapter we find out how variations are created and how they are passed on: how small changes pile up over the generations, which rules decide the features a child shows (Gregor Mendel worked them out with garden peas), and how the sex of a baby is decided.