Unit A: Biological Diversity
Section 2.0

Asexual and sexual reproduction Distinguish between sexual and asexual reproduction, and identify and interpret examples of asexual and sexual reproduction in different species
Compare sexual and asexual reproduction, in terms of the advantages and disadvantages.

Key terms: - Anther - Asexual reproduction - Binary fission - Budding - Cleavage - Cross-fertilization - Cross-pollination - Egg cells - Embryo - Fertilization - Gametes - Ovary - Ovule

Notes:
Asexual reproduction is any reproductive process that does not involve the combination of DNA. Asexual reproduction involves only one parent. All of the offspring are identical to the parent.
Binary fission is the simplest form of asexual reproduction. Cells divide equally. Only single-celled organisms reproduce in this way. The cell splits into two cells and each one is identical.
Ex: bacteria, amoeba, algae Budding is similar to binary fission, but cells do not divide equally. During budding, the parent develops a bud or smaller version of itself that eventually detaches and becomes a separate organism. Ex: hydra, yeast, coral (do not detach)
Spores allow offspring to develop at some distance from the parent.
Spores are similar to seeds, but are produced by the division of cells on the parent, not by the union of two cells. Ex: fungi, green algae, moulds, ferns. Vegetative reproduction can occur in both sporophytic (spore-producing) and gametophytic (gamete-producing) plants.
Vegetative reproduction is the reproduction of a plant not involving a seed, including; cuttings, runners, suckers, tubers. During vegetative reproduction, non-reproductive tissue is induced by environmental or physiological factors to produce a structure that will result in new copies of the parent plant. Ex: coleus plant, spider plants, strawberries, aspen, potatoes In the body cells of multicellular organisms mitosis is the process that ensures the division of a cell into two new cells identical to the parent cell. Sexual reproduction involves the exchange of DNA from two individual organisms, and usually takes place through gametes or sex cells (spermatozoa or sperm cells, and ova or egg cells). The offspring that are produced from this union have a mix of characteristics, half from one parent and the other half from the other parent. Gametes are formed by the process of meiosis, which occurs only in specialized reproductive tissue. During meiosis, a single cell undergoes two nuclear divisions.
Reduction division, where the amount of DNA is halved
And a division similar to mitosis, but with half the number of chromosomes compared to body cells of the species.
Meiosis gives rise to four gamete cells, all of which have half the DNA complement of a somatic (non-reproductive) cell.
Since the nuclei of the two gametes fuse during fertilization, the amount of DNA in the nucleus of the zygote is restored to the somatic level. Sperm cells and egg cells unite to form a fertilized combination of cells called a zygote. The zygote is the first of many cells of a new individual. The zygote will begin to divide into two cells and this continues to be repeated over and over resulting in the development of an embryo. This embryo develops into a multi-cellular organism inside the female (in most mammals) or, outside (in an egg shell) in other animals.
Sexual reproduction in plants involves gametes as well, male gametes and female gametes joining, during fertilization, to produce a zygote and then an embryo. Most plants produce both male and female gametes, while some produce one or the other only. Pollen contains the male gametes and is found on the stamen. Ovules contain the female gametes and are found in the pistil. Pollination occurs when pollen is transferred from the anther of the stamen to the stigma