Before a young one is born, its parents pass it instructions for how to grow.

The instructions are far too small to see. But here is what they say, written out as a list.

The lamb's instructions, written out as a list: grow white wool; grow a black face; grow short ears. Some lines came from the mother and some from the father.

One instruction says: grow white wool.

Another instruction says: grow a black face, and another says: grow short ears.

The mother passes instructions, and the father passes instructions too.

So the lamb grew a black face because its instructions said so, and those instructions came from its parents.

A trait a living thing had from the start, from its parents, is called an inherited trait.

The instructions set the inherited traits. A kitten's gray fur is set by instructions from its two parents too.

A gray cat and her gray kittens. The kittens' gray fur was set by instructions from both parents.