Download 9A Inheritance and Selection

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Inheritance and Selection
Variation
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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.
Where is this information stored?
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Genetic information is stored by genes which are arranged on
chromosomes:
Section of a chromosome:
Genes for
blood group:
Genes for
eye colour
Genes for
hair colour
Different species have different numbers
of chromosomes. Humans have 46 (23
pairs) in every cell.
Environmental differences
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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
Sexual reproduction
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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:
Sexual reproduction
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In plants, the gametes are the egg and pollen:
Fertilisation
Any type of sexual reproduction helps a species to become
more varied because the offspring inherit characteristics
from both parents.
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.
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Friesian
Jersey
If, for example, I want lots of
milk I would only breed
Friesian cows with each other
– this is SELECTIVE
BREEDING.
Hereford
Asexual reproduction
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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