Hi Joanna,
The cell cycle consists of the following stages: G1 -> S -> G2 -> M (this could be mitosis or meiosis).
The S phase (synthesis phase) is when DNA is replicated regardless of if we are going to do mitosis or meiosis.
Usually somatic cells will undergo mitosis whereas gamete cells will undergo meiosis. Gamete cells (sex cells) include your eggs cells and sperm cells.
In terms of X or Y chromosome: Somatic cells of a human female would have two X-chromosomes, somatic cells of a human male would have one X chromosome and one Y chromosome. Egg cells contain one X-chromosome, Sperm cells contain either an X-chromosome or Y-chromosome.
Fertilization is the fusion of an egg and sperm cell. The egg cell (ova) will be completing meiosis II before it fuses its nucleus with the nucleus of the sperm cell. The sperm cells however, have already finished Meiosis II at the time of fertilization. Its only the egg cell that is finishing meiosis II. Once the egg and sperm cells fuse, you get a diploid cell (zygote). The zygote will now grow through mitosis (i.e. go through G1, S, G2, M).
I hope this helps!
- Shin