The History and Science of Molecular Genetics

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The History and Science of Molecular Genetics

• Timothy G. Standish, Ph. D.

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ChromosomesThe Physical Basis of Inheritance

• 1866 Mendel published his work
• 1875 Mitosis was first described
• 1890s Meiosis was described
• 1900 Mendel's work was rediscovered
• 1902 Walter Sutton, Theodore Boveri and others
  noted parallels between behavior of chromosomes
  and alleles.
• 1910 Thomas Hunt Morgan associates a trait with a
  chromosome (white eyes on the Drosophila Y
  chromosome)

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Molecular GeneticsA Short History

• 1869 - Miescher isolated DNA for the first time
• 1944 - Avery provided evidence that DNA is the
  genetic material
• 1953 - Watson and Crick proposed the double helix
  as the structure of DNA
• 1957 - Kornberg discovered DNA polymerase
• 1961 - Marmer and Doty discovered DNA
  renaturation
• 1962 - Arber, Nathans and Smith discovered
  restriction endonucleases
• 1966 - Nirenberg, Ochoa, and Khorana figured out
  the genetic code.

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A Short History Cont.

• 1967 - Geller discovered DNA ligase
• 1972-73 - Boyer, Cohen and Berg develop DNA
  cloning techniques
• 1975 - Southern developed gel-transfer
  hybridization
• 1975-77 - Sanger and Barrel and Maxam and Gilbert
  developed rapid DNA sequencing methods
• 1981-82 - Palmiter and Brinster produced
  transgenic mice, Spradling and Rubin produced
  transgenic fruit flies
• 1985 - Mullis and colleagues invented the
  Polymerase Chain Reaction (PCR)

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What is Science?

• Sci Knowledge ence The condition of
• Explanation of natural phenomena through
  observation and experimentation
• A method of gaining knowledge (the scientific
  method)

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The Scientific Method

• The Scientific method relies on two types of
  reasoning
• Inductive reasoning - The drawing of generalized
  conclusions from a collection of data this is
  the type of reasoning used when coming up with a
  theory
• Deductive reasoning - Elimination of
  possibilities until only one or a very few
  remain. Hypotheses are testable statements that
  must be true if a theory is true, thus if the
  hypothesis is not true, the theory can be
  deducted from the set of possible theories.

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The Scientific Method
Beliefs
Hypothesis
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The Scientific MethodDoes Not Always Provide
Definitive Answers
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Understanding Science

• Scientists must understand the difference between
  facts (data) and interpretation (theory)
• Fact - Chimpanzees and humans have DNA that is 98
  - 99 identical
• Interpretation 1 - Chimpanzees and humans share a
  common ancestor
• Interpretation 2 - Chimpanzees and humans share a
  common Designer
• Most data is open to multiple interpretations
• Theory ? Fact

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Reductionism

• Organisms are too complex to study as a whole, so
  biologists break them down to their components,
  assuming that knowing each parts workings gives
  insight on the whole organism.
• Understanding the digestive system requires study
  of the digestive organs. Understanding the
  esophagus, stomach and intestines helps us
  understand the system.
• Cells, the fundamental units of life, can be
  understood in light of biochemicals (proteins,
  lipids, carbohydrates etc.) from which they are
  made.
• Selection works at the level of macro molecules,
  not on their chemical components

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Emergent Properties

• Biological systems are more than just the sum of
  their parts the combination of parts produce
  emergent properties only present because of the
  combination and not intrinsic to any single part.
• A wheel is not a transportation device and
  neither is a bicycle frame put them together
  with a few other parts and they become a bicycle.
• The heart would not pump blood if it was only the
  ventricles contracting, or just valves ensuring
  blood flows in only one direction. Combination of
  ventricles and valves moves blood through the
  heart and out to the body.

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Biologists Dilemma

• Life is too complex to study as a whole, thus
  reductionism must be used to simplify biological
  systems to the point they can be understood
• The simple components that make up living
  things have emergent properties present only when
  they are combined together.
• In other words, the whole is greater than the sum
  of the parts
• Understanding how the components work does not
  necessarily tell us how the organism works.

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The Limit of Reductionism?

• Because biologists cant know what other parts
  interact with the part they are studying without
  knowing some emergent properties of those parts
  together, it seems that in many (all?) cases
  understanding emergent properties on the basis of
  a parts properties is not possible
• This is not to say that emergent properties
  cannot be inferred from comparison of one part
  with another related part for which the function
  is already known

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Behes Insight

• Michael Behe contends that when we look at the
  protein machines that run cells, there is a point
  at which no parts can be removed and still have a
  functioning machine. He called these machines
  irreducibly complex (IC)
• We encounter irreducibly complex devices in
  everyday life. A simple mouse trap is an example
  of an irreducibly complex device

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Genetics

• In one sense, genetics could be considered to be
  the ultimate exercise in reductionism on the part
  of biologists.
• Genes serve as the blueprint for life. All
  proteins are defined by genes, and all other
  macromolecules are made by proteins.
• All emergent properties are ultimately defined by
  genes

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Genetics

• In one sense, genetics could be considered to be
  the ultimate exercise in reductionism on the part
  of biologists.
• Genes serve as the blueprint for life. All
  proteins are defined by genes, and all other
  macromolecules are made by proteins.
• All emergent properties are ultimately defined by
  genes

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Molecular Genetics

• Molecular genetics studies biology at the
  fundamental point where chemicals meet to produce
  the emergent property we call life
• Does understanding molecular genetics mean that
  we understand life?

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