Reproduction and variation
Asexual reproduction
Only one parent is needed in asexual reproduction. There is no fusion of Sex cell (sperm in males and ova/eggs in females)., so genetic material does not mix. This means that the offspring produced through this process are An organism that is genetically identical to another organism., ie they are genetically identical to the parent.
Examples of organisms that use asexual reproduction include:
- Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium.
- production of A unit of asexual reproduction in some organisms. by A large group of eukaryotic organisms that contain single-celled yeasts, moulds and mushrooms.
- some plants, such as strawberries, use runners
- formation of A swollen, fleshy underground stem of a plant, such as the potato, bearing buds from which new plant shoots arise. in potatoes and bulbs in daffodils
Mitosis
Asexual reproduction uses the process of A type of cell division which produces daughter cells identical to the parent. 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 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 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 A fertilised egg cell., 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.
More guides on this topic
- Classification and biodiversity – WJEC
- Cell division and stem cells – WJEC
- DNA and inheritance – WJEC
- Mutation – WJEC
- Evolution – WJEC
- The nervous system – WJEC
- Homeostasis – WJEC
- The role of the kidneys in homeostasis – WJEC
- Micro-organisms and their applications – WJEC
- Disease, defence and treatment – WJEC
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