Introduction to Evolution

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Introduction to Evolution
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Review of Meiosis

• 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.

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Do the math!

• 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.
• Dont forget that 2 sex cells are needed to make
  every person.

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Egg and Sperm Needed for Fertilization
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More math!

• 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!!

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The process of meiosis allows for genetic
diversity in a population!
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Mutations Also Increase Diversity

• 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 persons DNA
  created blue eyes.
• That trait was then passed down by meiosis!

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Meiosis and Mutations cause diversity in all
areas of nature.
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Charles Darwin

• In the 1830s 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.

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Finches

• 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.

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Observations

• 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.

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Natural Selection

• The finches that had traits that made them better
  adapted to their environment had a better chance
  to survive.
• The birds that didnt 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.

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Fitness

• 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 its environment.

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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 wont pass on their traits.

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Evolution

• Eventually natural selection will cause the
  traits of an organism to change over time.
• Change over time Evolution

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Evidence of Change Over Time

• 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.