REPRODUCTIVE SUCCESS
Learning Outcomes
After completing this lesson, you will be able to:
 Compare the advantages and
disadvantages of asexual and
sexual reproduction
 Describe situations where one
type of reproduction is more
advantageous than the other
 Determine whether an example
illustrates sexual or asexual
reproduction
 Explain the purpose of mating
call and courtship behaviour
 Describe adaptations of plants
and animal species that
enhance reproductive success
Reproduction
As you have learned,
plants and animals must
reproduce for several
reasons. One of the
reasons for reproduction
is survival of the
organism. Reproduction
can take place two ways,
either sexually or
asexually.
The table shown below gives you a brief summary of the
two methods of reproduction.
Asexual Reproduction
One parent
All genetic information is
passed to offspring from one
parent
Offspring is genetically
identical to parent
Genetic differences are rare
and come from mutations
Sexual Reproduction
Two parents
Each parent contributes
one-half the genetic
information to offspring
Offspring has combination of
genes from both parents
Allows greater genetic
variation since offspring will
always differ from parents
and other offspring
Reproduction exists in two forms but there are variations
within these forms. The chart shown below will help
demonstrate the variations in reproductive strategies.
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Asexual Reproduction
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Advantages and Disadvantages
Of Asexual Reproduction
Advantages
Disadvantages
Produces a new organism
 Does not give rise to genetic
that is genetically identical
variability in organisms of a
to its parent
same species
There is no need to find a
 The species does not adapt
partner
at all or adapts very slowly
when circumstances change
It takes energy to produce
offspring sexually
 There is only one parent to
take care of offspring
Offspring is usually well
adapted to its environment
 The parent sometimes
because of the success of
disappears because its body
the parent
no longer exists (fission)
An area favourable to the
 An asexual species runs the
parent can quickly be
risk of suddenly disappearing
colonized due to the high
because of a catastrophe that
number of offspring the
affects all organisms of the
parent can generate in
species that are genetically
little
identical
time
 Offspring are often already
multicellular and more
viable
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Sexual Reproduction



Advantages and Disadvantages
Of Sexual Reproduction
Advantages
Disadvantages
Produces a new organism
 Finding a reproductive
that results from a
partner and producing
combination of traits of two
gametes requires the output
parents
of a lot of energy
Increases the genetic
 Mechanisms for the transport
viability in organisms of the
of gametes for fertilization, for
same species and even
the attraction of the opposite
within the offspring of one
sex, and for competition
couple
within a species must be put
in place
In the long run, allows the
best adaptations to be
 Not only are two gametes
widespread within a
needed for fertilization, one
species, especially in
must be male and the other
changing circumstances
female
The variability of the
 The genetic results of
offspring within a species
meiosis, and often
guarantees that a higher
fertilization, are unpredictable
proportion will survive in
 Genetic “errors” happen more
perilous circumstances
frequently because meiosis is
more complex than mitosis is
Two parents can watch
over
and diploid organisms have
offspring
more chromosomes to double
 Offspring are not necessarily
as well adapted to their
environment as the parents
 Many organisms never
become parents because
they can’t find a partner;
many gametes are lost
because they are not
fertilized
Mutations
How do the two types of reproduction contribute to the
success of the organism?
Reproductive Success and Asexual Reproduction
Generally, primitive organisms use asexual reproduction.
Primitive organisms include bacteria, hydra, yeast, and
planaria as examples. Of course, every generalization has
exceptions. The exceptions in this case are plants that
reproduce by vegetative reproduction since they are
complex organisms.
There are some advantages to asexual reproduction.
 Every organism is capable of reproduction. Organisms
that reproduce asexually are capable of increasing
their populations at very high rates. We have all
experienced the effects of high reproduction rates in
bacteria. Bacteria are capable of reproducing both
sexually and asexually.
When conditions are
favourable, they choose
asexual reproduction for
its high rate of producing
new offspring. Our
throats offer a
favourable medium for
bacteria. We experience
this negative effect by
developing a sore
throat.
 Identical offspring take full advantage of a favourable,
static environment; no time or energy is wasted by
genetic variation.
 Plants and animals that cannot move are capable of
reproduction. Many primitive organisms are either
incapable of moving, or have limited mobility. Asexual
reproduction is an efficient method for them to
produce offspring.
Reproductive Success and Sexual Reproduction
 The most significant difference between asexual and
sexual reproduction is the genetic variation that
results from meiosis.
Do you remember during prophase in meiosis I that
“cross over” takes place? It is during cross over that
genetic information from both parents is exchanged in
the chromosomes. The gametes finish up with a
mixture of characteristics from both parents. There are
both costs and benefits to their method of
reproduction. The benefits must outweigh the costs
since sexual reproduction is the most common
method of producing offspring.
Some costs include:
1. The cost of producing males.
Only females reproduce. Males
take up 50% of any population.
Sexual reproduction does not
make particularly efficient use of
its resources.
2. Mating consumes time and
energy. Mating often makes the
individuals vulnerable to attack
from other animals.
3. Genetic variability can be
unnecessary in a static environment.
The benefit of genetic variation outweighs the costs.
1. Genetic variation is an advantage in an environment
that is under stress. Most environments are under
constant change. A species must be under constant
change to survive. The environmental and species
change referred to in this case usually takes place
over many years. We would not expect change to
take place over a few weeks.
2. Hermaphrodites have both reproductive organs in the
same plant or animal. While the organism reproduces
sexually, there is only one parent. Stationary plants
and animals may reproduce this way since their
immobility makes it difficult to find a mate.
3. Bacteria reproduce asexually under beneficial
environmental conditions. Bacteria are also capable
of reproducing sexually if the environment becomes
hostile. Bacteria reproduce sexually by a process
called conjugation. The conjugation, two bacteria
contact each other, form a bridge, and
exchange pieces of genetic
information contained in plasmids.
Plasmids are small loops of DNA that
can be transferred from one bacterium
to another.