3.2) Fertilization

Understand that fertilization involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

The process of fertilization begins with the adults male and female.

The cells in testis and ovaries both have complete set of chromosomes (called diploid, or 2n), meaning both have 46 chromosomes each.

Theses cells divide to form cells with half set of chromosome (23 each) in the process called meiosis. We go from a diploid number to a haploid number, n. 

This leaves us with 23 chromosomes in each sperm and egg cell.

In sexual reproduction, these two cells are brought together and are joined/fused to form just one cell. This process is known as fertilization. It involved a combining of half set and half set of chromosomes to form a full set of chromosome.

n + n = 2n

This cell is called zygote, which is combination of male and female chromosomes. 

The zygote then go through a process called mitosis in which the cell will divide to give two cells (in which both contains complete set of chromosome). As a result, all cells contain 2n/diploid number of chromosome. 

When we have sufficient cells, the structure would be called an embryo. 

Such process holds through for all sexually reproducing organisms.