3.2 Fertilisation

Key points:
1. The process begins with the adult male and the adult female. The cells which make up an adult have a complete set of chromosomes. Diploid means that they have a complete set of chromosomes. These cells divide in the testis to produce a half set and in males this is the sperm cell, and in females its the egg. This is known as meiosis, and this will half the number of chromosomes. From 2n -> n. So 23 chromosomes.
2. In sexual reproduction these two cells are brought together and they are joined together so that it forms just one cell. This process is known as fertilisation. It involes combining two half sets into one diploid. 23 from sperm + 23 from egg = 46 known as zygote.
3. This new cell is a combination of the male and female chromosomes. This goes through a process known as mitosis, where the cells will divide. One cell -> Two cells. They will both contain 46 chromosomes, and they will divide and the cell divisions will also have 46 chromosomes. All will contain 2n diploid number of chromosomes. Once there are a group of divided cells, this structure will be known as an embryo.