Download Introduction to Evolution

Introduction to Evolution
Review of Meiosis
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Humans have 23 pairs of chromosomes.
When you form sex cells, only one chromosome from
each pair gets passed along.
The chromosome that gets passed along is random for
each pair of chromosome.
Do the math!
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If there are 23 pairs of chromosomes and they
all separate randomly then there is a possible
223 (~ 8 Million) different types of sex cells one
person can make.
Don’t forget that 2 sex cells are needed to make
every person.
Egg and Sperm Needed for
Fertilization
More math!
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Sperm = 223 possibilities
Egg= 223 possibilities
Egg x Sperm=
223 x 223 =6.4 x 1013
There are a lot of different combinations just
two people can make!!
The process of meiosis allows for
genetic diversity in a population!
Mutations Also Increase Diversity
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Mutations are changes in a DNA
sequence.
Some mutations may cause a new trait.
New traits increase the diversity of a
population.
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Scientists believe that
millions of years ago all
humans had brown
eyes.
Then a random
mutation in one
person’s DNA created
blue eyes.
That trait was then
passed down by
meiosis!
Meiosis and Mutations cause
diversity in all areas of nature.
Charles Darwin
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In the 1830’s Darwin
sailed aboard the HMS
Beagle and landed on
the Galapagos Islands.
He observed different
animals and plant
species and drew them
in his notebook.
He took a particular
interest in Finches.
Finches
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Darwin observed that
there were several
different types of
finches that occupied
different parts of the
islands.
What they looked like
depended on where
they lived on the
island.
Observations
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Darwin observed that
the different finches had
special traits that
helped them survive in
their environment.
For example, birds who
at tiny insects had long,
thin beaks and birds that
ate large seeds had big,
strong beaks.
Natural Selection
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The finches that had traits that made them
better adapted to their environment had a
better chance to survive.
The birds that didn’t get the traits needed to
survive in their environment died.
Darwin called this concept ‘Survival of The
Fittest’ which today we refer to as
NATURAL SELECTION.
Fitness
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Since not all finches have the same traits,
some finches will be better adapted to their
environment than others.
Darwin said that finches that were better
adapted to their environment had better
‘fitness’ because they can out-compete the
other finches.
Fitness= The ability of an organism to
survive and reproduce in it’s environment.
Which Giraffe is more fit?
The giraffes that are more
‘fit’ will survive and
pass on their traits to
their offspring.
The giraffes that are not
‘fit’ will most likely die
and won’t pass on their
traits.
Evolution
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Eventually natural
selection will cause the
traits of an organism to
change over time.
Change over time =
Evolution
Evidence of Change Over Time
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If you look at the fossil
record, you can see that
species have changed
over time.
Example, the fossil
record shows that the
anatomy and bone
structure of the horse
had changed over time.