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CHANGES IN THE GENETIC CODE
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Ectrodactyly
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What do they all have in common?
They’re all mutations!
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MUTATIONS a change in the DNA code
causes a different (sometimes wrong) type of protein to be made may or may not be good for the organism
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ALONG THE WAY good changes occur bad changes occur
changes that don’t matter either way
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CHANGE IS NECESSARY without changes we would all look alike
without changes we would not evolve without changes we would not develop immunities to disease SO… Is change/variation a good thing??? YES!
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Causes of Variation Crossing Over Mutations Some happen randomly
Some caused by Mutagens (agents that cause mutations) Nuclear Radiation Ultraviolet Light X Rays
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CROSSING OVER occurs when homologous chromosomes trade segments
occurs during Prophase I of Meiosis
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entire gene is switched
involves the variation of a single trait gene for big ears exchanges with gene for small ears
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Advantages variation of offspring from parents
allows for “good” changes Better chance of passing on genes for survival
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3 TYPES OF MUTATIONS Chromosomal mutations Gene mutations
Somatic mutations these usually occur during mitosis and involve a chromosomal mutation involved with body cells, not sex cells tumors are the result
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Research your mutation
1. Answer these questions What does the name of the mutation mean? What happens to the chromosome? What is an example?
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CHROMOSOMAL MUTATIONS
NONDISJUNCTION DELETION INVERSION DUPLICATION TRANSLOCATION INSERTION
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NONDISJUNCTION failure of homologous pairs to separate during meiosis
correct number of chromosomes are not present in the gamete after fertilization, diploid number is not restored
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Examples Trisomy 21(Down Syndrome)- 3 copies of chromosome 21
Klinefelters Syndrome- XXY Turner Syndrome- X “Supermales” - XYY
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DELETION A SEGMENT OF A CHROMOSOME IS DELETED
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Examples Cri-du-chat syndrome- “cry of the cat”- deletion of piece of chromosome #5 Angelman Syndrome- deletion of piece of chromosome #15 Prader-Willi Syndrome- deletion of piece of chromosome #15
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INVERSION A SEGMENT OF THE CHROMOSOME IS FLIPPED IN THE OPPOSITE DIRECTION
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DUPLICATION A SEGMENT OF THE CHROMOSOME IS COPIED TWICE
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TRANSLOCATION SEGMENTS FROM TWO DIFFERENT CHROMOSOMES ARE SWITCHED
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Example Translocation Down Syndrome
Instead of being 3 separate copies of chromosome 21, the extra copy is actually attached to another chromosome
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INSERTION A SEGMENT OF ONE CHROMOSOME IS INSERTED INTO A DIFFERENT CHROMOSOME
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GENE MUTATIONS POINT MUTATIONS FRAME SHIFT INVERSIONS insertions
deletions INVERSIONS
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LETS MUTATE! GCC TTA CGT TTA CGA CTG TAC GTA
Start with an original strand of DNA GCC TTA CGT TTA CGA CTG TAC GTA CGG AAT GCA AAT GCT GAC ATG CAT A B C D lets assume this strand codes for a protein AMINO ACIDS
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POINT MUTATIONS TTA CGT TTA CGA AAT GCA AAT GCT ORIGINAL
1 base is replaced with another base TTA CTT TTA CGA AAT GAA AAT GCT MUTATION B E
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Example Sickle Cell Anemia- changing 1 base causes mutation that codes for valine instead of glutamate in the protein hemoglobin Individuals produce different type of hemoglobin Red Blood Cells become sickle shaped and don’t pass thru blood vessels as easily Cells die sooner than normal Individuals don’t get as much oxygen
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http://www. montgomerycollege
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FRAME SHIFTS TTA CGT TTA CGA AAT GCA AAT GCT ORIGINAL A B C D
TTA CGT TTA ACG A AAT GCA AAT TGC T INSERTION-base is inserted A B C F TTA CGT TAC GA AAT GCA ATG CT DELETION- base is deleted A B G
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INVERSIONS TTA CGT TTA CGA AAT GCA AAT GCT ORIGINAL A B C D
Codon is found in reverse order TTA TGC TTA CGA AAT ACG AAT GCT INVERSION A H C D
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Consequences Sometimes mutations are bad and cause for different proteins to be made But- if you look at the amino acid chart- several different codons code for the same amino acids Mutations can occur but wouldn’t be noticed Some mutations are masked by other genes
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