Reproduction and variation
Asexual reproduction
Only one parent is needed in asexual reproduction. There is no fusion of , so genetic material does not mix. This means that the offspring produced through this process are , ie they are genetically identical to the parent.
Examples of organisms that use asexual reproduction include:
- production of by
- some plants, such as strawberries, use runners
- formation of in potatoes and bulbs in daffodils
Mitosis
Asexual reproduction uses the process of to create the identical copies (clones) of the parent cell.
It therefore leads to offspring that show no genetic variation.
Sexual reproduction
Sexual reproduction requires two parents, a male and a female, each of which produce gametes. Fertilisation is the fusion of the of a male gamete with the nucleus of a female gamete.
In humans, each gamete has half the total of 46 chromosomes that the body requires. We refer to 23 chromosomes within a gamete as haploid.
When the two gametes combine, they merge the two sets of chromosome to have 46, which are referred to as diploid.
This produces a new cell called a , which will mature into an embryo. The number of cells increases by mitosis, and as the embryo develops, the cells begin to differentiate (or specialise).
As half of the genetic make-up of the offspring is from one organism and half from another, it is genetically different from its parents. In other words, it shows variation.
