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Variation
Variation is a name given to differences in a species, e.g. dogs:
Variation is due to each animal having different GENETIC
INFORMATION in their cells.
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Where is this information stored?
Section of a chromosome:
Genes for
eye colour
Genes for
hair colour
Genes for
blood group:
Different species have different numbers
of chromosomes. Humans have 46 (23
pairs) in every cell.
Genetic information is stored by genes which are arranged on
chromosomes:
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Environmental differences
Clearly, not all differences are due to just our genes…
Variation due to
inheritance only
Variation due to
environment only
Variation due to a
bit of both
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Sexual reproduction
Sexual reproduction involves two organisms of the same
species. Each organism produces a GAMETE.
For example, in animals
the gametes are the egg
and the sperm:
When the sperm penetrates the egg the egg is fertilised and
cells start to reproduce to form a new individual:
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Sexual reproduction
In plants, the gametes are the egg and pollen:
Any type of sexual reproduction helps a species to become
more varied because the offspring inherit characteristics
from both parents.
Fertilization
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Selective breeding
I raise cows. Each type of
cow is good at a certain job.
The Friesian cow produces
large quantities of milk, the
Jersey cow produces very
nice milk and the Hereford
cow produces lot of beef.
If, for example, I want lots of
milk I would only breed
Friesian cows with each other
– this is SELECTIVE
BREEDING.
Friesian
Jersey
Hereford
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Asexual reproduction
Plants can reproduce ASEXUALLY. The offspring are
genetically ________ to the parent plant and are called
_________. Two examples:
1) This spider plant has grown a rooting
side branch (“stolon”) which will
eventually become __________.
2) A gardener has taken cuttings of
this plant (which probably has good
characteristics) and is growing them
in a ____ atmosphere until the
____ develop.
Words – clones, damp, independent, roots, identical
