Chromosomes through the generations

You will write two small functions for the chromosomes of gametes and of a zygote. Then you will use them on four organisms, and check that the number stays the same.

The idea. A gamete carries one chromosome of each pair, half the body-cell number. A zygote gets one gamete from each parent.

Your tasks.

1. In gamete, return the number of chromosomes in a gamete of an organism whose body cell has n.
2. In zygote, return the number in a zygote formed from gametes with a and b chromosomes.
3. Fill the dictionary gametes with the gamete number of every organism in body_cells.
4. Set constant to True if, for every organism, a zygote from two of its gametes has the body-cell number again.