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Section 5.2: Asexual Reproduction

Asexual Reproduction• requires one parent • it is a process where one parent makes clones of itself to produce new organisms (offspring) that are identical to each other and the parent from which they came. • There is no sexual intercourse involved.• No new genetic diversity. (This may be an advantage or disadvantage - why?)• Creatures that reproduce this way include microorganisms, moulds, sea sponges, and other groups we consider “less highly evolved”.

Modern science ( bioengineering ) uses our understanding of asexual reproduction methods to develop cloning technology. We asexually copy organisms that are desirable to us...like cows that produce more milk, prize winning ornamental plants or livestock, race horses, etc. Bioengineers also clone individual skin cells to grow new tissue for burn victims. To date, it is considered illegal and unethical to clone a human.

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Types of Asexual Reproduction

One celled organism (unicellular) such as the amoeba depend on asexual reproduction to reproduce themselves in great numbers. The amoeba and other one cell organisms are part of the food chain for more complex organisms. Because of this role, it is necessary that they reproduce in large numbers.

Types of Asexual Reproduction include...Binary fissionFragmentationBuddingVegetative reproductionSpore formation

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1. Binary fission

A single parent cell becomes two cells by copying its genetic material, then splitting into, becoming two cells.

Ex. Algae in water and bacteria (Prokaryotic organisms)Amoebas (a single cell Eukaryotic organism)

Prokaryotic cells - their genetic material is often a ring ( a “plasmid”) of a moleculecalled DNA found somewhere in the cell cytoplasm.

Eukaryotic cells - have DNA molecules inside their nucleus

Amoeba

http://www.youtube.com/watch?v=gEwzDydciWc&feature=related

Bacteria

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2. Budding

A growth (or bud) forms on the parent, develops and may or may not pinch off to produce another cloned organism.

Good for some creatures that are attached to objects and don‛t move themselves (like sea sponges and hydra), or fast growing unicellular creatures like yeasts.

The problem with this method is that if the young do not move some distance away from the parent, crowding and competition increases with time.

Ex. Sea HydraEx. Yeast :

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3. Fragmentation

• If an organism (the parent) breaks apart, each fragment then develops into a clone of itself.Do not confuse with regeneration. - Regeneration: Organisms can use mitosis to re-grow lost body

parts. For example, a salamander can re-grow its tail if lost.- In fragmentation a whole new organism is grown. This organism is a clone of it parent.

Examples.... starfish, planarians, Japanese knotweed ( page 157)

Star fish - If a star fish is cut in two each piece may be able to develop into another star fish if it contains enough of the parent's genetic information.

A planarian -

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4. Vegetative Reproduction

Special groups of cells, usually in plants stems and plant roots, divide repeatedly to form structures (new root tissue) that will eventually develop into a plant identical to the parent.

Examples: Potato eyes, Strawberry "runners", Tulip "bulbs", Plant "Cuttings", "Grafts"

Potato eyes Strawberry "runners"

Lupines Tulip Bulbs

Perhaps you have seen a farmer plant the “eyes” of potatoes. Maybe you have planted tulip bulbs. Planting bulbs or the eyes of potatoes are ways of reproducing plants. This is called vegetative reproduction. These new plants are identical to the parent plants.

A runner connects these strawberry plants. This plant part is a stem that “runs” across the top of the soil.  New strawberry plants grow at certain points where the runner touches the ground.  Strawberries spread out in a field because runners stretch out in all directions.

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Artificial Vegetative Reproduction

People grow plants vegetatively for many reasons. Plants grow faster from vegetative parts than from seeds. Some kinds of plants, such as seedless grapes and oranges, can only be grown from vegetative parts. Vegetative reproduction has also allowed plant growers to produce better kinds of plants. Plant growers have developed methods of vegetative reproduction that do not occur in nature. These include layering, cutting and grafting.

In layering, a person covers with soil a branch that has one or more buds. Each bud grows into a new plant that can be cut away. Rose bushes and raspberries are reproduced by layering.

            Cuttings are stems, roots, or leaves that are cut off a plant and placed in water, sand or soil. These cuttings grow and develop into whole plants. Many houseplants, such as geraniums, African violets are reproduced in this way.

Sometimes plant growers cut off a piece from the top part of a plant and attach it to the root system or stem of another plant. This method is called grafting.

Grafting involved joining the hardier parts of one plant to the hardier parts of another plant. For example, one kind of rose bush may have a well-developed root system but poorly formed flowers. Another may have beautiful flowers but a poor root system. A plant grower can make a hardier rose bush by grafting together the best parts of each plant. Grapes and fruit trees also are reproduced by grafting.

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Disadvantage.... offspring grow close to the parent, adds to the competition levels.

Advantage.... Easy to transplant and grow crop plants this way, or clone certain individuals with good traits.

5. Spore Formation

A "spore" is a single reproductive cell, enclosed in a environmental tough outer capsule, capable of growing into a new individual by mitosis. Spore producers rely on water or wind tp carry the spores away from the parent. They grow wherever they land IF the conditions are favorable.

Examples: mosses, ferns, some bacteria (bread mould), fungi

Bread Mould

P

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Ferns

Peat Moss

Puff Ball Fungus

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Advantages and Disadvantages of Asexual Reproduction

Advantages  Disadvantages

Large numbers of offspring are reproduced very quickly from only one parent when conditions are favorable.

Offspring are genetic clones. A negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring.

Large colonies can form that can out­compete other organisms for nutrients and water 

Some methods of asexual reproduction produce offspring that are close together and compete for food and space.

Large numbers of organisms mean that species may survive when conditions or the number of predators change.

Unfavorable conditions such as extreme temperatures can wipe out entire colonies. 

Energy is not required to find a mate. 

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