How can human egg cells be gametes when they are diploid until ovulation?

[marek]

As I understand this: a fertilized zygote inherits one set of chromosomes from the egg cell and a second set from the sperm. However, despite the fact that the egg cell only contributes one set of chromosomes to a fertilized zygote, the egg cells in the ovaries actually have two full sets of chromosomes (diploid), and are halted in prophase I of meiosis. During ovulation and fertilization, the egg cells complete meiosis and shed three sets of chromosomes as polar bodies while retaining the one set of chromosomes that are contributed towards the zygote.

 

The piece that has be confused is this:

 

Egg cells are considered gametes, gametes are haploid, yet egg cells are diploid except for a brief moment during the fertilization process.

 

This seems to be self-contradictory. Can someone explain this? thanks!

 

[CharonY]

In your description you are missing oogenesis. The primary oocyte is diploid, but then matures into the haploid ovum (via secondary oocyte).