Asexual Reproduction
Asexual reproduction is a form of reproduction which does not involve
fertilization. Only one parent is involved in asexual reproduction. Asexual
reproduction is the primary form of reproduction for single-celled organisms such
mold and bacteria. Many plants and fungi reproduce asexually, as well. There are
even a few animals that reproduce this way!
ADVANTAGES
Because asexual reproduction skips the processes of making gametes (eggs and
sperm) and then fertilization, it happens much faster than sexual reproduction
and requires less energy. Asexual reproduction can make many offspring very
quickly. It is also an advantage to be able to reproduce without a partner. This is
helpful in situations where the population is low, which reduces the chance of
finding a mate. It also helps during colonization of isolated habitats such as
islands, where a single member of the species is enough to start a new
population. Overall, asexual reproduction is quick and easy, and can happen in
very low populations.
DISADVANTAGES
A consequence of asexual reproduction is that offspring are typically genetically
identical to their parent. This results in fewer genetic varieties than sexual
reproduction. This is not advantageous if the environment is changing. For
example, if a new predator or disease appears and an organism is particularly
defenseless against it, every organism that reproduces asexually will have the
same exact ability (or lack of) to deal with it. Asexual offspring are more likely to
be completely wiped out by a new threat. Another downside of asexual
reproduction is that offspring numbers are often very large, creating tons of
competition for resources within the species itself.
TYPES OF ASEXUAL REPRODUCTION
Binary Fission
Many single-celled organisms (unicellular), such as bacteria and protists, reproduce asexually through
binary fission. The cell copies its contents, including its nucleus and other organelles, and then splits into
two cells with each one being identical. The process of binary fission is quite simple – the organism
literally divides itself into two organisms.
Amoeba Undergoing Binary Fission
Budding
The parent organism produces a bud (a smaller version of itself), which eventually detaches itself from
the parent and becomes a self-sufficient individual that is identical to the parent. Some cells split via
budding (for example baker's yeast used to make bread rise), resulting in a 'mother' and 'daughter' cell.
An animal that reproduces by budding is the water-dwelling creature called hydra. The offspring
organism is smaller than the parent, but the bud eventually grows into a fully mature individual that
eventually breaks away from the parent. Coral also reproduces in this way, but do not detach
themselves.
Budding Hydra
Spore Formation (Sporogenesis)
Many multicellular organisms form spores during their life cycle in a process called sporogenesis. Spores
are similar to seeds but are produced by the division of cells on the parent, not by the union of two cells
by fertilization. One parent may produce many spores, each of which may grow into a new individual,
identical to its parent. Fungi (mushrooms), green algae, bread molds and ferns are some of the
organisms that use spores to reproduce.
Fragmentation (AKA Regeneration)
Fragmentation is a form of asexual reproduction where a new organism grows from a fragment of the
parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in
organisms such as animals (some annelid worms and starfish), fungi, and plants.
Vegetative Reproduction (Plants Only)
Vegetative reproduction is a type of asexual reproduction found in plants where new individuals are
formed without the production of seeds or spores. Examples of include the formation of plantlets on
specialized leaves (for example in kalanchoes and spider plants), the growth of new plants out of
rhizomes (for example in strawberry), or the formation of new bulbs (for example in tulips). Asexual
reproduction in flowering plants is common. The next examples provided are all types of vegetative
reproduction.
Ex. Rhizomes - Plants such as the grasses, cattails and sedges produce underground stems or
rhizomes. As these stems grow through the soil, they will periodically produce roots and a new above
ground shoot. A new separate plant will form.
Ex. Tubers - Tubers are actually modified rhizomes. They are formed in such plants as potatoes. They
develop when specialized stem branches grow down into the ground and swell up with starch containing
cells. Buds on the tubers will grow into new plants. Examine the potato tuber and note the buds which
are commonly termed "eyes".
Ex. Runners - These are horizontally growing stems that produce few, if any, leaves. At the spot
where a leaf would normally develop a node, these plants will produce roots down into the soil, and
new above ground shoots. Examine the strawberry plant to the right. Note the runner and the new
shoots.
Ex. Plantlets - A few plants such as the duckweed, spider plant and kalanchoe produce miniature
plants on the end of their leaves. These drop off and develop into mature plants. The duckweed, which
is an aquatic plant, reproduces almost entirely by this method.
Ex. Bulbs - Onions, chives and lilies over-winter in the form of a bulb. Each bulb has a very short stem
which surrounded by fleshy leaves. In the spring, the shoot apex begins to grow using the nutrients
stored in the bulb. Plantlets Bulb