Asexual Reproduction
• Now that you have seen the cell cycle
(how cells reproduce) and meiosis (how
gametes are formed) you can have a
better understanding of asexual and
sexual reproduction.
• As mentioned earlier, there are different
types of asexual reproduction. We are
going to discuss these in detail.
What is Asexual Reproduction?
• Asexual reproduction is a mode of
reproduction by which offspring arise from
a single parent, and inherit the genes of
that parent only; it is reproduction which
does not involve meiosis or fertilization.
• http://en.wikipedia.org/wiki/Asexual_reprod
uction
Binary Fission
• The simplest form of asexual reproduction, in
which a parent organism divides into 2 equal
cells.
• Usual method of reproduction among unicellular
organisms such as bacteria, algae, and protists.
• Involves 2 distinct phases:
i) duplication of genetic material. In cells with a
nucleus, the nucleus divides by mitosis.
ii) division of the cytoplasm into 2 equal parts.
- paramecia undergo "binary fission”
- See handout
Budding
• A type of asexual reproduction in which the
parent organism divides into 2 unequal parts.
• New organisms develop as small outgrowths or
buds on the parent organism.
• The buds may break off and live independently
or remain attached forming a colony.
• Budding occurs in yeast, hydra, sponges and
some worms.
Budding Hydra
Sponge Colony
Spore Formation
• Spores are single specialized cells
produced by certain organisms that when
released, germinate and grow to form new
individuals.
• Spores are usually tiny special cells with a
hard protective wall around them. Other
spores lack walls and may be flagellated.
• Spores may be formed asexually or
sexually.
• Asexual spores are formed by the nucleus
of a single-celled organisms breaking up
into many nuclei. A cell wall develops
around each nucleus and part of the
cytoplasm forming the spore.
• Spore formation occurs in fungi, algae and
protozoa.
• Large numbers of spores are generally
produced.
Fragmentation
• A new organism grows from a fragment of
the parent.
• Each fragment develops into a mature,
fully grown individual.
• Fragmentation is seen in many organisms
such as animals (some worms, and sea
stars), fungi, and plants.
Regeneration
• Regeneration is the ability of an organism to re-grow lost
body parts.
• Simple animals when cut into 2 or more parts have the
ability to regenerate each part into a complete organism
• Starfish can be cut into several pieces and if each piece
gets enough of the central disk, they will all develop into
new individuals.
• Powers of regeneration decrease as animals become
more complex.
• Lobsters and crabs can re-grow a lost claw but cannot
generate a whole animal from a small piece.
Vegetative Propagation/
Reproduction
• Vegetative reproduction is a type of asexual
reproduction found in plants where new
individuals are formed without the production of
seeds or spores by meiosis
• It includes the processes in which
undifferentiated plant cells divide by mitosis and
then differentiate to form an independent plant.
• http://en.wikipedia.org/wiki/Asexual_reproductio
n.
Vegetative Propagation
• A root or leaf is used to develop a new
plant.
• May occur naturally or by artificial means.
• There are different types of natural
vegetative propagation. We will study
bulbs, tubers, runners and rhizomes.
1. Bulbs
• Short underground stem surrounded by
thick fleshy leaves that contain stored food
• When placed in earth a bulb will produce a
new plant.
• Tulips, onions, and lilies reproduce by
bulbs
2. Tubers
• An enlarged portion of an underground
stem that contains stored food.
• White potatoes are tubers
• Potato “eyes” are buds that if planted will
grow into a potato plant
3. Runners
• Horizontal stems with buds that grow close
to the ground
• When buds from the runners touch the
ground, roots and leaves develop to form
new plants
• E.g. strawberries, many grasses
4. Rhizomes
• Stems that grow horizontally underground
• Thick and fleshy and contain stored food
• Nodes are enlarged portions along the
side of the rhizomes, which produce buds
• The buds develop roots from the lower
surface and leaf bearing branches from
the upper surface.
• Ginger, ferns, irises, cattails, and
waterlillies reproduce by rhizomes.
Ginger
Types of Artificial Vegetative
Propagation
1.
–
-
(how people can clone/grow plants)
Cuttings
any vegetative part of a plant; leaf, stem, or root used
to produce a new individual
In a stem cutting, a branch/slip is cut from a plant and
placed it in water or moist sand
Cutting soon develops roots and leaves to form a new
complete plant
Geraniums, roses, ivy and grapevines may be
propagated this way.
In leaf cutting, a leaf or part of a leaf is placed in water
or moist soil.
A new plant develops from certain cells in the leaf. E.g.
African violets
2. Layering
– A stem is bent over so that it is covered in
soil
- After the covered part forms roots, the
new plant may be cut from the parent plant
- Layering is used to reproduce raspberries,
roses, and honeysuckles.
3. Grafting
– a stem or bud removed from one plant and
joined permanently to the stem of a closely
related plant.
- The plant providing the roots is called the
stock
- The added piece is called the scion
- The growing regions of the scion and the
stock must be in close contact
- Although grafting is a type of reproduction,
nothing new is produced by the process.
- The scion retains its own characteristics
- Used to propagate roses, peach trees,
plum trees, and navel oranges.
Advantages of artificial propagation:
1. Ensures that new plants are exactly like
the parent
2. Plants bearing seedless fruit can be
grown only by vegetative propagation
3. Grafting is used to obtain higher yields of
fruits or nuts
Cultivated plants propagated by vegetative
methods:
A number of commonly cultivated plants are propagated
by vegetative means rather than by seeds. This is a
listing of such plants:
Apples, Bananas, Cannabis, citrus, dates, grapes,
figs, pineapples