ASEXUAL REPRODUCTION REVIEW SHEET

Objectives Explain the term asexual reproduction. Highlighting the various types of asexual reproduction. Discuss the advantages and disadvantages of asexual reproduction. Explain the principles and importance of vegetation propagation as exemplified by the use of cutting and tissue culture. Discuss the genetic consequences of asexual reproduction

What is Asexual Reproduction?Asexual reproduction is the type of reproduction that produces offspring by a single organism without the production or fusion of gametes. It usually results in the production of genetically identical offspring to the parent and are referred to as clones.

Types of Asexual ReproductionThere are various types of asexual reproduction. These include: Binary FusionFusion is the division of a cell into two or more parts and the regeneration of these separate parts into new separate cells. Therefore binary fusion is the division of a cell into two parts and the regeneration of the parts to form two separate cells. The circular DNA in the cell begins to replicate and the original replicating DNA is attached to different parts of the cell membrane. The cell will eventually expand and divide into two identical daughter cells. Binary fusion most commonly occurs in bacteria. Example of binary fusion in bacteria:Steps bacteria take to carry out binary fusion I. The bacterium cell must copy its DNA so the new cells will have DNA. DNA or, deoxyribonucleic acid, has all of the information the bacterium will need to survive, so it is important it gets copied. The DNA is tightly wound so it is in a neat package called a chromosome. II. The bacterium now grows larger. This allows for some separation between the two DNA copies that are inside the cell. A division develops in the middle of the bacterium. This division eventually completely divides the bacterium in half. This is called cytokinesis.III. Each cell is now called a daughter cell and they separate

FragmentationFragmentation or clonal fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning in which an organism is split into fragments. Each of these fragments develops into mature, fully grown individuals that are clones of the original organism. Example: Sea stars regenerate their arms, lizards regenerate their tails.

Interesting FactMany species of annelids (worms) reproduce via an asexual process called fragmentation. Included in this category of worms are California blackworms, or mudworms. These worms are hermaphroditic -- they have both male and female reproductive parts -- and can reproduce sexually. However, many times these worms will reproduce using fragmentation. In this case, blackworms can break apart and each consequential fragment can become a new worm.

Budding A form of asexual reproduction in which a new individual produced as an outgrowth (bud) of the parent, and is later released as an independent, identical copy of the parent. It involves the replicating of the DNA of the cell and enclosing the replicated DNA into a much smaller amount of cytoplasm and cell membrane than the original parent cell. Therefore a daughter cell that is much smaller than the parent is produced but is genetically identical. Examples : The Hydra produces via budding

Spore FormationThis type of asexual reproduction occurs in Fungi. The typical body structure of fungi is a mass of fine tubes called hyphae. The whole mass of hyphae is called mycelium. At the tips of hyphae are spores that are enclosed in a special structure called sporangium, or free spores. Spores are small structures that contain a nucleus. They are produced in large numbers and are very light; therefore they can easily be dispersed by either animals or by the wind. After the spores are dispersed via wind and animals should they land in favorable conditions (warmth, water and oxygen), they will germinate and develop into new plants.

Vegetation Propagation The most common form of asexual reproduction is called vegetation propagation. This is the form of asexual reproduction in which a bud grows and develops into a new plant.

Methods of vegetation propagation include: Cutting Tissue Culture

CuttingThis is a an artificial means of asexual reproduction. The procedure involves the removing a part of the plant by cutting and placing it in a suitable medium for growth. It produces roots and grows into a new plant.

Types of Cutting Stem cutting: the plants side shoot is cut right across. This is the area a leaf joins the stem. The piece of stem and at least one leaf node buried in the soil. Overtime the cutting produces new roots at the node. Example: Sugar cane Root cutting: the plant is cut across its root. The section of the root that is cut is buried beneath the soils surface. Overtime new shoots are emerged. Example: Breadfruit

Tissue culturePlant tissue culture is the collection of techniques used for the growth of plant cells. The leaf is first placed in disinfectant solution to ward off bacteria. Small pieces of tissues are extracted from the leaf. The explant is exposed to a culture of liquids. Hormones: controls the growth of the tissues and its development into the roots stems and leaves of the new plants. For example auxin Nutrients: such as sucrose provides energy for the group of cells and other sterile nutrients such as potassium. The explants are remained under sterile conditions until they are big enough to resist infections from fungi. After periods of time, the cells in explant form calluses through the process of mitosis. The calluses are then placed onto a sterile agar jelly that contains nutrients which activates the development of roots and shoots. The mixture in the solution changes overtime during different stages of growth in the cells. When the plant becomes large enough to fend for itself, it is placed into sterile soil in order to complete its growth process.

Importance of Vegetation Reproduction

The desired trait of the parent plant is preserved among the stock of plants. It is an economical way obtaining the desired variety. Tissue culture produces disease free plants in a short time. It is beneficial to agriculturists who grow crops that do not produce seeds. It allows the multiplied species to become well adapted to their new environment

Advantages of Asexual Reproduction Only one parent is required- neither a mate nor the mechanism of pollination is required. Genetically identical offspring the offspring are genetically identical to the parent, so all the characteristics of the parent are passed on to its offspring and its genes are preserved. Dispersal and Spread- asexual reproduction enables a species to be dispersed over a area. This allows the species to find new feeding grounds as well as new habitats. Rapid Multiplication- Asexual Reproduction is capable of producing large quantity of offspring at a vast rate. For example, Bacteria can divide as often as once every 20 minutes allowing numbers to build up very rapidly.

Disadvantages of Asexual Reproduction No genetic variation occurs among the offspring therefore they are unable to adapt to environmental changes and this can result in the entire specie not surviving such changes. Is spores are produced, many will fail to find suitable place for germination and so energy and materials used in their manufacture are wasted. If an organism spread in one area, it may result in overcrowding and exhaustion of materials as well as an increase in competition for food

Genetic Consequences of Asexual Reproduction

An invasion of a disease can wipe out the entire plant species. They cannot adapt to changes in the environment. There is competition for natural resources.