Reproduction is the production of new individuals so that the species may be continued. The new individuals are either exact copies of the parent or may show some amount of variation from the parents, depending on the type of reproduction involved.
Sexual reproduction
This type of reproduction occurs in the majority of animals and plants. It involves the fusion of male and female gametes produced by meiosis. Gametes are sex cells that carry genetic information from one generation to the next. These genes determine the characteristics of new individuals. The zygote that results from the fusion of the gametes divides by mitosis to form the new organism. (The Hutchinson Dictionary of Science, 1998)
Sexual reproduction results in genetic variation:
- The parents' genes are organized into new combinations in the gametes during meiosis
- Both males and females produce gametes, which have different combinations of genes
- The gametes fuse at random
- The resulting offspring have gene combinations that differ from the parents.
The main advantage of genetic variation is that it allows natural selection. The species can adapt through the process of natural selection to new environmental conditions.
The disadvantages of sexual reproduction are that:
- Identical offspring, apart from twins, cannot be produced
- Favorable characteristics in a species cannot be propagated
- The presence of both sexes is required
- The rate of population increase may be relatively slow or non-existent if two parents produce only one offspring.
Asexual reproduction
A large number of plants reproduce asexually, but many of these also reproduce sexually. Some animals, mostly single-celled ones, reproduce asexually. New individuals are produced from one parent by mitotic cell division. This results in clones, individuals that are identical to their parent and to one another. Gametes are not required for asexual reproduction. (The Hutchinson Dictionary of Science, 1998)..........
