Unit A Reproduction

Advantages and Disadvantages of Sexual Reproduction
The most important advantage of sexual reproduction is that the offspring are
genetically different from their parents and from each other. This variation allows
individual organisms to adapt to changes in the environment. If the environment
changes in some way, there will be a few individuals who have small differences
that allow them to survive in the new environment. They will survive to
reproduce and pass on the traits that helped them survive to their offspring. For
example, throughout human history, there have been outbreaks of new diseases,
which have killed large numbers of people. In each outbreak, however, some
people who were exposed to the disease were able to fight it. They survived
to reproduce and passed on their ability to fight the disease to their children.
A disadvantage of sexual reproduction is that an individual needs to find a
mate. Without a mate, no offspring can be produced. Sexual reproduction also
tends to produce fewer offspring than asexual reproduction. As well, sexual
reproduction can be a lot slower. Most organisms that reproduce sexually
have to grow and develop before they start to produce gametes. For example,
female orcas need to grow and develop for eight to ten years before they can
reproduce (Figure 5).
Advantages and Disadvantages of Asexual Reproduction
There are several advantages of asexual reproduction. If a parent does well in
its environment, the offspring will also do well in the same environment because
the offspring are genetically identical to the parent. Another advantage is that
only one parent is necessary. A parent does not have to find a mate in order
to reproduce. Therefore a parent can reproduce frequently, and can produce
a large population in a relatively short time. For example, a bacterium living
in your gut has a warm environment with plenty of food. It can take advantage
of these conditions and reproduce itself very rapidly, about every 20 minutes.
Through binary fission, it can produce millions of offspring in just 24 hours.
This rapid reproduction means that all the daughter cells can take advantage
of the same good conditions.
Producing genetically identical offspring can also be a disadvantage. If the
environment changes, all the offspring will be affected the same way as the
parent. For example, when you take an antibiotic, all the millions of
important bacteria produced through binary fission in your gut are killed if
they have no resistance to the antibiotic.
Table 1 summarizes the features of asexual and sexual reproduction.
Table 1
A comparison of asexual and sexual reproduction
Feature Asexual reproduction Sexual reproduction
Number of parents one two
Number of offspring usually many few to many
Variety of offspring genetically identical genetically different
Speed of reproduction usually fast usually slow
Timing anytime, once mature once mature, only when a mate
is available
Figure 5 This juvenile orca, seen
swimming above its mother, will not
be able to reproduce for several years.
Did You
KNOW?
Cool Kittens
The environment influences many
genetic traits. Fur colour in Siamese
cats is influenced by temperature.
The kittens are born white. The cooler
parts of the body (face, ears, paws,
and tail) will turn a darker colour
than the rest of the body as the
kittens grow.
LEARNING TIP
Tables help readers identify specific
information quickly. As you study Table 1,
ask yourself, “How is the information
organized?” Think about what is being
compared. Ask yourself, “What is the
basis of the comparison between
asexual and sexual reproduction?”
NEL
3.2 Sexual Reproduction and the Diversity of Life 81