Sexual reproduction, meiosis and gamete formation
Meiosis
Sexual reproduction uses a type of cell division called Reduction division in a cell in which the chromosome number is halved from diploid to haploid., which creates Sex cell (sperm in males and ova/eggs in females)., such as sperm and egg cells. The process of meiosis happens in the male and female reproductive organs. Just like in A type of cell division which produces daughter cells identical to the parent., a cell starts meiosis in interphase. In interphase, the DNA is copied, the cell grows and the organelles are copied too. After interphase:
- two meiotic divisions occur which means the cell divides twice to form four gametes
- each gamete has half the number of chromosomes found in body cells (one chromosome from each pair), and so is known as A sex cell (gamete) that contains one set of chromosomes.
All gametes are genetically different from each other.
Comparing meiosis and mitosis
| Mitosis | Meiosis |
| 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 |
| Mitosis | Diploid cells made |
|---|---|
| Meiosis | Haploid cells made |
| Mitosis | Used for growth and repair |
|---|---|
| Meiosis | Used for sexual reproduction |
| Mitosis | Cells made are genetically identical to starting cell and each other |
|---|---|
| Meiosis | Cells made are genetically different to starting cell and each other |
| Mitosis | Two cells are produced |
|---|---|
| Meiosis | Four cells are produced |
| Mitosis | One division occurs |
|---|---|
| Meiosis | Two divisions occur |
| Mitosis | Interphase happens before cell division |
|---|---|
| Meiosis | Interphase happens before cell division |
Sexual reproduction
Two parents are needed in The formation of a new organism by combining the genetic material of two organisms.. During this process the nuclei of the male and female gametes are fused in order to create a A fertilised egg cell.. This process is known as The joining of a male and female gamete..
The gametes in:
- animals are eggs (female) and sperm (male)
- flowering plants are eggs/ovules (female) and found inside pollen (male)
The offspring produced in sexual reproduction are To do with the genes that an organism contains. different to each other and the parents. This process results in variation as it involves the mixing of genetic information.
Fertilisation in humans
Fertilisation is the fusion of the The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei. of a male gamete 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 A cell that contains two sets of chromosomes. 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 An organism in the early stages of development.. 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 Difference between individuals, distance from the norm. into a A type of organism that is the basic unit of classification. Individuals of different species are not able to interbreed successfully..
The zygote grows by mitosis to form an embryo. As the embryo develops, the cells begin to When an unspecialised cell becomes a more specialised cell type..