Download Asexual Reproduction - CAPE Biology Unit 1 Haughton XLCR 2013

Asexual
Reproduction
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, ploidy reduction,
or fertilization.
ASEXUAL REPRODUCTION
• involves one parent only.
• Parent cell splits into two to
produce
new
cells
(MITOSIS).
SEXUAL REPRODUCTION
• Involves two parents (male
and female).
• Two sex cells (gametes)
made by MEIOSIS fuse to
form the offspring.
• Offspring therefore identical
to the parent (CLONE).
• Offspring
therefore
has
characteristics from both
parents but are not identical
to the parents or one
another.
• Results in a lack of variation
and diversity between parent
and offspring and among
offspring.
• Results in variation and
diversity between parent and
offspring
and
among
offspring.
• Gametes and fertilization are
NOT required.
• Gametes and
ARE required.
fertilization
What is asexual
reproduction?
• A more stringent definition is
agamogenesis which refers to
reproduction without the fusion of
gametes. Asexual reproduction is the
primary form of reproduction for singlecelled organisms such as the archaea,
bacteria, and protists
• The different modes through
which asexual reproduction takes
place are binary fission, spore
formation, vegetative reproduction
and budding.
Advantages of asexual
reproduction
• 1. Large numbers of offspring are reproduced very
quickly from only one parent when conditions are
favourable.
• 2. Large colonies can form that can out-complete other
organisms for nutrients and water.
• 3. Large number of organisms mean that species may
survive when conditions or the number of predators
change.
• 4. Energy is not required to find a mate
Disadvantages of asexual
reproduction
• 1. Offspring are genetic clones. A negative mutation can
make asexually produced organisms susceptible to
disease and can destroy large numbers of offspring.
• 2. Some methods of asexual reproduction produce
offspring that are close together and compete for food
and space.
• 3. Unfavourable conditions such as extreme
temperatures can wipe out entire colonies.
Vegetative Reproduction
• Vegetative reproduction is a form of
asexual reproduction in plants, where
parts of the plant fall off and develop into
new plants. Potato tubers are one
example of a plant that used this form of
reproduction. Since asexual reproduction
doesn't require another partner, or pollen
transfer it is very quick and is guaranteed.
Vegetative Reproduction
• This is very good for people using potatoes in
their products, because reproduction is very fast,
so they can make more potatoes, and hence
make more money. The main disadvantage of
this form of reproduction, is that the new plants
will all grow very close to each other and to the
parent. This will cause a struggle for soil,
nutrients and light, and will consequently cause
the plants to be less healthy.
POTATO
ASEXUAL: NATURAL VEGETATIVE PROPAGATION
• Occurs when new plants are formed from the
outgrowths of old ones.
• Examples are:
• Runners where the stems run horizontally from a
plant and new plants form at nodes (strawberry,
pumpkin).
• Bulbs are underground buds and new buds grow
from the parent one (onion).
• Plantlets are tiny plants that grow along the margins
of certain leaves. Eventually the plantlets fall off and
develop into new plants (the Leaf of Life).
RUNNERS
BULBS
PLANTLETS
ASEXUAL REPRODUCTION:
ARTIFICIALVEGETATIVE PROPAGATION
•
Gardeners and farmers often use artificial
means when they want to propagate more
of a plant that is of good quality because
the offspring will be identical to parent.
• These methods include:
1. Cuttings
2. Grafting
ASEXUAL REPRODUCTION: ARTIFICIAL
VEGETATIVE PROPAGATION
•
Gardeners and farmers often use artificial
means when they want to propagate more
of a plant that is of good quality because
the offspring will be identical to parent.
• These methods include:
1. Cuttings
2. Grafting
PROPAGATION BY CUTTINGS
Parts of a plant
are cut off and
given suitable
conditions so
developing
their own roots
and shoot and
become a new
plant.
Examples
are
sugarcane,
yam
and
hibiscus.
PROPAGATION BY GRAFTING
• A shoot (the scion)
from a young plant
bearing fruits or
flowers is attached
to the stem of an
already
established
root
system (the stock).
The new plant that
grows
has
beneficial
characteristics of
both the stock and
scion e.g. mango,
citrus and rosebushes.
SPORE FORMATION
Vegetative Propagation
It is a process where a plant can reproduce
asexually, with the use of a vegetative part of the
original plant. This process can occur naturally.
It can also be done manually, and is especially
beneficial when one wants to create new plants
from fruit or vegetable parent plant. Vegetative
propagation techniques have been used with
varying degrees of success, in attempts to help
developing countries produce larger sources of
food for the population.
• We all are accustomed with growing new
plants from seeds. No doubt, seeds are
one of the most versatile means for
producing new plants. However, the major
drawback of seed propagation is that
some species of plants either do not
produce seeds or majority of the seeds are
not viable. In such cases, vegetative
propagation becomes very important.S
Advantages of Vegetative
Propagation
• The offspring produced are generally
identical, and hence, the more beneficial
characteristics can be preserved.
• In this gardening process only one parent
is required, unlike sexual reproduction
methods like pollination.
• Vegetable propagation is faster.
• Many plants produced are able to suffice during
unfavorable conditions. This is due to the
presence of organs which help in asexual
reproduction like bulbs and tubers.
• This process of propagation is especially
beneficial to horticulturists and agriculturists, as
they can raise various fruits and vegetable
plants without requiring to buy seeds.
• With modern techniques of tissue culture
combined, one can grow virus free plants.
Cutting Method Of Vegetative
Propagation
• Propagating plants from cuttings method is
also called as striking or cloning, in which
a piece of plant containing at least one
stem cell is placed on suitable medium like
soil, potting mix or rock wool. This cutting
helps to produce new roots, stems or both,
and develops into a new plant.
Stem Cutting
• Stem cuttings can be taken from the main stem
or the side branches of the plant. Different types
of stem cuttings are:
• Herbaceous Cutting - Houseplants like
chrysanthemum, rhododendron and geranium
are propagated by herbaceous cutting. For this
type, rooting is easy and the growth phase has
nothing to do with root formation. So, you can
make stem cuttings at any time, when the plant
is growing actively. More on ways for
propagating rhododendron.
Stem Cutting
• Softwood Cutting - This cutting is made
from the new stem growth of the current
season and is easy to promote rooting.
Deciduous shrubs like lilac, plum, rose and
forsythia are propagated by softwood
cuttings.
• Semi-Hardwood Cutting - Broad-leaved
evergreens like azalea, camellia, olive,
citrus and holly are propagated by semihardwood cutting. This method refers to
cutting made from the stem growth of the
current season, when the stem is not
completely mature or hard.
• Hardwood Cutting - Over here, the hard
stem of the previous year is used for
propagation. Hardwood cutting is taken at
a specific time of the year, particularly
during winter when the plant is inactive or
dormant. Deciduous and narrow-leaved
evergreens like privet, honeysuckle,
quince, grape, cypress etc. are
propagated by the hardwood cutting
method.
Leaf Cuttings
• Leaf cuttings can be made anytime from the
plant. A healthy and disease free leaf is cut
smoothly from the plant, which is then used for
generating a new plant. Unlike stem cuttings that
require only rooting, both shoot development
and root formation are necessary in case of leaf
cuttings. Not all plants can be propagated by
means of leaf cutting. Rather we can say
propagation by leaf cutting is successful for a
few plants like houseleek, rex begonia and
sansevieria.
Root Cutting
• Plant propagation by root cuttings is also limited
to a few species of herbaceous plants, shrubs
and bushes and trees. Examples of plants that
can be propagated by this method include
raspberry, blueberry, globe thistle and acanthus.
First, healthy roots of specific size
(approximately the diameter of a pencil) are
exposed and cut in sections of about 1 ½ - 3
inch in length. In order to avoid confusion while
placing the root cutting in growth medium, the
first top cutting should be made flat and the
bottom cutting should be diagonal.
Micropropagation/Tissue Culture
• This method is practiced to multiply a stock plant
at a rapid rate, to produce a large number of
progeny plants using the modern plant culture
methods. Plant tissue culture encompasses
culturing of plant parts on an artificial medium.
The plant parts can be a single cell, tissue or an
organ. It is also referred to as micropropagation.
Plant tissue culture was practically implemented
for the first time by Haberlandt, a German
scientist, in 1902. Later in 1934, Gautheret found
successful results on in-vitro culture of plants.
Micropropagation/Tissue Culture
• The basic key used in plant tissue culture
is the totipotency of plant cells, meaning
that each plant cell has the potential to
regenerate into a complete plant. With this
characteristic, plant tissue culture is used
to produce genetically identical plants
(clones) in the absence of fertilization,
pollination or seeds.
Micropropagation/Tissue Culture
• In plant tissue culture, plants or explants such as
pieces of leave, stem or root is cultured in a
specific plant medium, which contains essential
plant nutrients and hormones. Other plant
growth factors like light and temperature are
maintained and regulated by using artificial
conditions. All the procedures of plant tissue
culture are conducted under sterile (aseptic)
conditions. The explants then develop stem,
roots and leaves. The generated plantlets are
hardened before planting in outdoor conditions.
Micropropagation/Tissue Culture
ASEXUAL REPROUCTION IN
ANIMALS
ASEXUAL REPRODUCTION
• Various types of asexual reproduction are:
•
•
•
•
•
•
•
Binary fission (animal)
Budding (animal)
Fragmentation and segmentation (animal)
Parthenogenesis (plant, animal)
Vegetative propagation (natural, plant)
Vegetative propagation (artificial, plant)
Sporulation (plant, fungi)
ASEXUAL: BINARY FISSION
• Occurs is protists such as the Amoeba and in bacterial
cells.
• The parent cell splits into two identical daughter cells by
mitosis.
ASEXUAL: BUDDING
• Occurs in protists and fungi such as yeast.
• The daughter cell buds or pinches off from the
parent as a smaller replica (clone) then grows to
mature size.
ASEXUAL: FRAGMENTATION and
SEGMENTATION
• Occurs in flatworms (fragmentation) and ringed
worms (segmentation).
• Parent organism breaks into different fragments or
segments, which form new individuals.
ASEXUAL: PARTHENOGENESIS
• The growth and
development of an
embryo or seed
without fertilization
by a male.
• Occurs naturally in
some lower plants,
some invertebrates
(e.g. water fleas,
aphids) and some
vertebrates
(e.g.
lizards,
salamanders, some
fish,
and
even
turkeys).
• Parthenogenetic
populations
are
typically all-female.
Fragmentation
• Fragmentation is another form of asexual
reproduction in animals. This is when an
organism is broken into 2 or more pieces,
and each one grows into a new individual.
For this type of reproduction the organism
must have good powers of regeneration.
Fragmentation
Fragmentation
Fragmentation
• This could be a disadvantage if the plant is
in poor conditions, as it wouldn't have
good powers of regeneration, and so it
wouldn't be able to reproduce. On the
positive side, it can produce many new
individuals very quickly
Binary Fission
• A method of asexual reproduction that is
employed by most prokaryotes. In binary
fission, the living cell divides into two
equal, or nearly equal, parts. It begins
when the DNA of the cell is replicated.
Binary Fission
• Each circular strand of DNA then attaches
to the plasma membrane. The cell
elongates, causing the two chromosomes
to separate. The plasma membrane then
invaginates (grows inward) and splits the
cell into two daughter cells through a
process called cytokinesis.
CLONING
• Cloning is an example of artificial asexual
reproduction.
CLONING
CLONING
Genetic Consequences of
Asexual Reproduction
• A consequence of asexual reproduction,
which may have both benefits and costs,
is that offspring are typically genetically
similar to their parent, with as broad a
range as that individual receives from one
parent.
• The lack of genetic recombination results
in fewer genetic alternatives than with
sexual reproduction.
Genetic Consequences of
Asexual Reproduction Cont`d
• Many forms of asexual reproduction, for
example budding or fragmentation,
produce an exact replica of the parent.
This genetic similarity may be beneficial if
the genotype is well-suited to a stable
environment, but disadvantageous if the
environment is changing.
Genetic Consequences of
Asexual Reproduction Cont`d
• For example, if a new predator or
pathogen appears and a genotype is
particularly defenseless against it, an
asexual lineage is more likely to be
completely wiped out by it. In contrast, a
lineage that reproduces sexually has a
higher probability of having more members
survive due to the genetic recombination
that produces a novel genotype in each
individual.
Genetic Consequences of
Asexual Reproduction Cont`d
• Similar arguments apply to changes in the
physical environment. From an
evolutionary standpoint, one could thus
argue that asexual reproduction is inferior
because it stifles the potential for change.
However, there is also a significantly
reduced chance of mutation or other
complications that can result from the
mixing of genes.
Videos of Asexual Reproduction
• http://www.youtube.com/watch?v=tWfgpH
KP0_4&feature=related
• http://www.youtube.com/watch?v=9moBpp
hvzOI&feature=related
• http://www.youtube.com/watch?v=drcnTg7
ZCoc
Questions & Answers
• Question: What is asexual reproduction?
• Answer: Asexual reproduction involves
only one parent and the offspring is
genetically similar to the parent.
• Question: Name the types of
reproduction that produces genetically
identical offspring?
• Answer: Asexual reproduction is the
type of reproduction that produces
genetically identical offspring.
• Question: What are the different types of
asexual reproduction?
• Answer: The different types of asexual
reproduction are binary fission, budding,
fragmentation, spore formation and
vegetative propagation.
• Question: What is binary fission?
• Answer: When the parent cell divides
into two cells that are almost identical, it is
called binary fission.
• Which diagram above represents binary
fission?