Page 20 - CB1.3 Genetic Varation sciPAD

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20 CB 1.3 GENETIC VARIATION
PRINCIPLES OF GENETIC VARIATION
Asexual Reproduction
All living things need to reproduce (produce offspring) in order
to ensure the continued survival of their species. Reproduction
can be defined as the creation of a new individual or
individuals from previously existing individuals. There are two
main methods by which organisms reproduce: ‘asexual’
reproduction and ‘sexual’ reproduction.
Asexual reproduction needs only one parent (usually a
female). The offspring are identical to the parent and to
each other and are known as ‘clones’. Asexual reproduction
is more common in plants than in animals, although there
are some animals that can reproduce this way. Potatoes
and strawberries can both reproduce asexually. The main
advantage of asexual reproduction is that it is an efficient
method of reproducing (no time or energy is spent looking for
a mate), which means the individual can exploit favourable
conditions (lots of food and space, etc.) very quickly.
However, because the clones are all identical (there is no genetic variation), if the environment
changes, or they are exposed to a new disease, they may have little chance of survival.
1. Define the term asexual reproduction. 


2. Outline why asexual reproduction doesn’t lead to variation in the offspring. 


3. In New Zealand, most of our commercial pine forests are grown from clones.
(a) Name the type of cell division occurring between stages 2 and 3 in the diagram
above. 
(b) Discuss the genetic advantage of using clones rather than seeds. 





(c) Discuss the major disadvantages of relying on pine trees that are all genetically
identical (clones). 





1 Cuttings are taken from
carefully selected trees.
Small sections of tissue are
removed from the cutting.
2 The sections of tissue are
grown in a nutrient mix
that contains hormones to
promote root growth.
3 The sections of tissue grow
into new trees, all being
genetic clones of each other.
An aphid giving birth to a clone
of itself. Asexually reproduction
means aphids can quickly exploit an
abundant food source.
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