Question

How does crossing-over increase variation in genes

Answer 1

This question is talking about Prophase 1, of Meiosis.

Toward the beginning of Meiosis,
the chromosomes that you get from you MOM
and the chromosomes that you get from your DAD
will wrap around each other.

And when they wrap around each other,
they actually break off, and trade bits and pieces of themselves, with one another.

We call this whole process CROSSING OVER.

In the end,
each of your chromosomes has a piece from another chromosome,
attached onto it.

This increases variation,
because in a sense, it creates new chromosomes.