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Transcript
Genetics and Evolution:
Hey, Aren’t Those Chapters in Different
Parts of the Book?
?
Just to review…
In general terms:
– Genetics is the science of heredity. It explains
how traits are passed from parents to
offspring.
– Evolution is the study of the historical
progression of a related group of organisms.
Evolution works through the process of
natural selection.
Natural selection is the process through
which the traits that are most likely to help
an organism survive and reproduce
become more common in a given
population.
Examples of Natural Selection include:
– Antibiotic resistance in bacteria
– Pepper moths in England during the Industrial
Revolution
– Galapagos Finches
So, what does all of this have to do
with genetics?
In order for natural selection to work, there
has to be something to select from!
These choices are created by the genetic
variability that exists in populations.
The other important factor of natural selection
is environmental change.
If there is no environmental change, no one
trait is selected over another because there
nothing that makes one trait an advantage
over another one.
So, natural selection works by…
1. Having variation
in heritable traits.
2. Environmental change
leads to selection of some
traits over others
X
X
X
XX
X
3. Parents with
4. The more advantageous
advantageous traits pass
traits become the most
them to offspring.
common.
Eventually…
The population may change such that
there are no alleles left for the nonadvantageous traits. They can disappear
from the population completely.
X
X
This can lead to speciation
Imagine there is a
storm that blows
1,000,000 of our bug
to one island and
1,000,000 to another
island.
Island 1 has lots of
food, but most of it is
high up in trees.
Island 2 is very
similar to the island
the bugs came from.
After many generations
Island 1
Bugs from Island 1
developed long legs
and hooked feet do
that they can easily
climb trees to get to
food.
Island 2
Bugs from Island 2
remained very similar
to their ancestors
who settled on the
island after the storm.
Where does the variation come
from?
The genetic variation comes from random
mutations in the genes.
The mutations occur when DNA replicates.
– Insertions
– Deletions
– Frame Shifts
– Inversions
– Point Mutations
In summary,
– DNA mutations create new alleles
– Alleles are recombined through sexual reproduction
producing new traits
– As environments change, different traits may become
dangers or advantages
– The parents with advantageous traits are more fit so
they have more offspring (some of which will have the
advantageous trait)
– Though many generations, the advantageous traits
will become more and more common in the
population