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How Traits Change Over Time
Natural Selection
vs.
Artificial Selection
Charles Darwin (1809-1882)
Sailed around the world 1831-1836
What did Darwin observe?
 The diversity of living
species was far greater
than anyone had
previously known.
 Each island had its own
type of tortoises and birds
that were clearly different
from other islands
 Each species seemed to be
adapted to the particular
environment in each
island.
Darwin’s Conclusions
 Survival of the Fittest
 Organisms best adapted to their environments will
be more likely to survive, reproduce, and pass
their desirable traits on to offspring
 NATURAL SELECTION
 Nature “selects” for genes that allow organisms to survive
and reproduce
How does Natural Selection work?
 Lots of offspring
 Lots of variation
Thousands of frog eggs are laid in clumps in a fresh
water pond. Each clump is laid by one female. Few
will survive to adulthood.
 Variation is a change that makes a difference in the
way an organism looks or acts, which might be
helpful or harmful
 Survival of the fittest; Not everybody
survives
Results of Natural Selection
 Organisms survive to pass on desirable traits.
 Over time, populations of organisms become
better adapted to their environment by this
process of natural selection.
EXAMPLE:
This species of insect is well adapted (carries the right
genes) to blend into its environment.
This is an example of
Mimicry.
Do you see the walking stick insect?
It received those genes from its parents, whose genes were
successful enough to allow them to survive long enough to breed.
Cats which are small
and not aggressive
Cows to produce
more milk
How has MAN changed the traits of
organisms ? Artificial Selection
Dogs have been breed to be friendly
Gold-colored fish
Horses for speed
If you wished to breed the prettiest
guppies, how would you do it?
By only selecting the most colorful guppies and
those with the longest tails, then breeding them
generation after generation.
Wild guppies
Guppy which has been
selectively bred.
Artificial Selection-Selective Breeding
 Selective Breeding: the process of breeding plants
and animals for particular desirable traits.
 Desirable traits are traits that we want or desire
in a plant or animal.
 Also called Manmade selection
 Examples:
 Dog Breeding
 Breeding for high milk
producing cows
 Breeding for food with desirable traits
Dog breeders have been selectively
breeding for desirable traits for centuries.
Selective Breeding
 Nature provides variation, humans select variations
of genes that are useful.
 Example - a farmer breeds only his best dairy cows
Farmers have cultivated many popular
vegetables from wild mustard,
by artificially selecting for certain attributes.
Hybrid Fruits
Nectarcots
Pluots
Tangelo
How many types of
apples are there?
 Why do we want to
produce hybrid
fruits?
 We want the desirable
traits of both fruits in
one!
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Artificial Selection-Genetic Engineering
• Genetic Engineering: Change the DNA of an
organism directly by inserting DNA from one
organism to another.
 Using genetic engineering you can make:
 New organisms
 Modified organism
 Examples:
 Glow in the dark cats
 Insulin producing bacteria
 Genetically modified foods
Insulin producing
bacteria
 Insulin is a chemical
humans need to process
sugar. Diabetics need to
take insulin.
 Human insulin gene is
inserted by genetic
engineering into the DNA
of bacteria
 Bacteria produce the
human insulin.
Tomatoes have been genetically modified to slow the
ripening process to prevent softening and rotting, while
allowing the tomato to retain its natural flavor and color.
Other examples
 Web Spinning Goats
 Vaccines in Bananas
 Pollution fighting plants
 Oil-spill cleaning bacteria
 Genetically Modified Trees to grow faster, yield better
wood and even detect biological attacks.
 Genetically Modified Plants have been genetically
engineered to resist herbicides, produce internal
pesticides, or increase their protein production
12 bizarre examples of genetic engineering