Answer:
"Last week, you looked at both animal & plant cells. Both of these cells were diploid somatic eukaryotic. This week, you'll be looking at a different, but very important, type of cell: sexual cells. Two gametes, one from a female & one from a male, merge during the process of fecundation/fertilization to form a zygote. All in the organism will develop from this initial diploid cell".
Explanation:
There are two principal types of cells in the organism: Somatic cells that can not form any gametes, and germ cells that are in charge of gamete production. Both somatic cells and germinal cells will end their cycle dividing and becoming two daughter cells with the same genetic dotation after mitosis.
Somatic cells are any cell in the body excepting from sperm and egg cells. These somatic cells are diploid, they contain two chromosomes sets, each one inherited from each parental. Mutations in somatic cells affect the individual but the progeny does not inherit them. In this sense, these cells do not contribute to anything to inheritance terms through genetics.
Germ cells are the reproductive diploid cells, and the sexual organs (testes and ovaries) are the ones that produce them. These cells might suffer mitosis to form more sexual cells, and then a few of them suffer meiosis giving place to haploid gametes called sperm and egg cells through the gametogenesis process. Each germ cell produces 4 haploid gametes after meiosis.
Gametes´destiny is to merge in the process of fecundation, during which a new diploid cell called zygote emerges through fertilization. The zygote is a complete cell from the structural point of view that suffer successive mitosis to form the new organism.
