Sexual reproduction uses a type of cell division called meiosis, which creates gametes, such as sperm and egg cells. The process of meiosis happens in the male and female reproductive organs. Just like in mitosis, a cell starts meiosis in interphase. In interphase, the DNA is copied, the cell grows and the organelles are copied too. After interphase:
All gametes are genetically different from each other.
|Diploid cells made||Haploid cells made|
|Used for growth and repair||Used for sexual reproduction|
|Cells made are genetically identical to starting cell and each other||Cells made are genetically different to starting cell and each other|
|Two cells are produced||Four cells are produced|
|One division occurs||Two divisions occur|
|Interphase happens before cell division||Interphase happens before cell division|
The gametes in:
The offspring produced in sexual reproduction are genetically different to each other and the parents. This process results in variation as it involves the mixing of genetic information.
Fertilisation is the fusion of the nucleus of a male gamet with the nucleus of a female gamete. In humans, each gamete has half the number of the total 46 chromosomes that the body requires. The 23 chromosomes within a gamete are referred to as a haploid.
When egg and sperm cells combine in fertilisation, they merge the two sets of chromosomes, ending up with 46 chromosomes in total. The maternal chromosomes from the egg cell and the paternal chromosomes from the sperm cell pair up.
The resultant cell is called a zygote. It is diploid as it has two copies of every chromosome - one came from the sperm cell and one came from the egg cell.
The zygote will mature into an embryo. It has DNA from both the mother and the father so will have a mixture of characteristics from both parents. In this way, sexual reproduction introduces variation into a species.
The zygote grows by mitosis to form an embryo. As the embryo develops, the cells begin to differentiate.