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					Mistakes in the code
                  Review:
• What does DNA look like?
• How is DNA made?
• How does DNA instruct the cell to make
  proteins?
• What determines the order of amino acids in a
  protein?
• What happens if you change an amino acid in
  the sequence of a particular protein?
• Why?
               Mutations
Mutation- a change in the DNA
 nucleotide sequence

Mutations can be silent (have no effect),
 cause subtle, or dramatic effects on
 observed traits in individuals
     How does your DNA determine
             your traits?

   DNA        mRNA         protein      Observed
                                          trait



  Remember:

1. Traits are determined by the functions of proteins
2. Protein function is determined by protein shape
3. Protein shape is determined by amino acid sequence
  Mutations can change the amino
    acid sequences of proteins
DNA sequence:          TACCGAGATTCA
mRNA sequence:         AUGGCUCUAAGU
amino acid sequence:   Met -- Ala -- Leu -- Ser


DNA sequence:                T
                       TACCGAGATTCA
mRNA sequence:         AUGGCUAUAAGU
amino acid sequence:   Met -- Ala -- Iso -- Ser
How does this mutation change the
     amino acid sequence?
 (Original)
DNA sequence:          AATGCATATGCA
mRNA sequence:         UUACGUAUACGU
amino acid sequence:   Leu -- Arg -- Ile -- Arg

 (Mutated)
DNA sequence:          AATTCATATGCA
mRNA sequence:         UUAAGUAUACGU
amino acid sequence:   Leu -- Ser -- Ile -- Arg
            3 types of mutations

Substitution              T
                    TACCGAGATTCA
                Substituting one nucleotide for another.

Insertion                  T
                    TACCGA GATTCA
                Inserting one or more nucleotides

Deletion            TACCGA GATTCA
                Deleting one or more nucleotides
               Your Turn
• Complete the “Mutations practice”
  worksheet. You will learn how some
  mutations can affect the amino acid
  sequence of proteins

• Consider how severe of an effect each
  mutation would have on the ability of the
  protein to function.
                 Questions
1. Which type of mutations had the biggest effect
   on the protein sequence? WHY?
2. Which type of mutations had the smallest
   effect on the protein sequence? WHY?
3. Which examples would you predict to have the
   biggest effects on a trait? WHY?
4. Which examples would you predict to have the
   smallest effects on a trait? WHY?
5. What is a possible explanation for the
   occurrence of these mutations?
Different types of mutations happen

Substitution         T
               TACCGAGATTCA

Insertion             T
               TACCGA GATTCA


Deletion       TACCGA GATTCA
           Frameshift mutations
•   One or more than one nucleotide can be
    added or deleted with insertion and deletion
    mutations.
•   If the number of nucleotides is not a multiple
    of 3, it is called a frameshift mutation.

1. Why do we call this a frameshift mutation?
2. Can substitution mutations cause
   frameshifts? Explain why or why not.
 Consequences of mutations…


• As a result of mutations, small differences
  exist between 2 organisms DNA
  sequences!
 How much variation in DNA exists
      between 2 people?
Hemoglobin (beta) gene sequence from person A
 How much variation in DNA exists
      between 2 people?
Hemoglobin (beta) gene sequence from person B
 How much variation in DNA exists
      between 2 people?
• About 1 in every 1,000 nucleotides is
  different between 2 people

• (0.1% difference means 99.9% identical)

• We have about 3 billion nucleotides in all,
  so that means there are about 3 million
  nucleotide differences between 2 people
    What is the observed effect of
              mutations?
•   No Effect
    (think about it: are there 3 million differences between 2 people?)

  – Why?
      1. Some mutations code for the same amino
         acid
      2. Most mutations are in sequences of DNA
         between genes.
• Variation – For any trait in a population there
   is variation within that trait as a result of small
   sequence differences (DNA            Amino Acids)
           Genetic diseases
• Most changes are harmless, but some can
  cause specific diseases.
• One way to determine whether a disease
  is inheritable is to trace the family history
  of a disease by creating a type of family
  tree called a pedigree.
• One inheritable disease caused by a
  specific substitution (or “point”) mutation is
  sickle cell anemia.
                   Questions
    Q. We’ve studied transcription, translation, and
    replication. A mistake in which of these
    processes would result in a permanent mutation?
•     Mitosis and Meiosis are about replicating
      the DNA. Mistakes in these processes
      can cause permanent changes in the
      DNA.
•     Can you inherit mistakes in either of
      these processes? Why/why not?
    Mistakes can be inherited
• If a mutation in sperm or egg DNA is not
  corrected, the new sequence of DNA is
  passed on to offspring.
• Over generations, mutations accumulate
  and species can slowly change their
  appearance.

				
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