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Mutations chapters 8 and 12
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What Are Mutations? Changes in the nucleotide sequence of DNA
May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring
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Types of Mutations
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Chromosome Mutations May Involve:
Changing the structure of a chromosome The loss or gain of part of a chromosome
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CROSSING OVER when the DNA from one chromosome
becomes attached to another chromosome - usually this occurs on HOMOLOGOUS CHROMOSOMES during PROPHASE I of MEIOSIS GENETIC RECOMBINATION- change in the genes or at least the location of genes
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Chromosome Mutations Five types exist: Deletion Inversion
Translocation Nondisjunction Duplication
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Deletion Due to breakage A piece of a chromosome is lost
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Inversion Chromosome segment breaks off Segment flips around backwards
Segment reattaches
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Duplication Occurs when a gene sequence is repeated
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Translocation Involves two chromosomes that aren’t homologous
Part of one chromosome is transferred to another chromosomes
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Translocation
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Nondisjunction Failure of chromosomes to separate during meiosis
Causes gamete to have too many or too few chromosomes Disorders: Down Syndrome – three 21st chromosomes Turner Syndrome – single X chromosome Klinefelter’s Syndrome – XXY chromosomes
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LAW OF INDEPENDENT ASSORTMENT
during meiosis I- one homologous chromosome travels to each cell. The chromosomes are chosen at random but the odds you get all 23 from the same parent is unlikely.
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Chromosome Mutation Animation
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Gene Mutations Change in the nucleotide sequence of a gene
May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc.
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Types of Gene Mutations
Include: Point Mutations Substitutions Insertions Deletions Frameshift
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Point Mutation Change of a single nucleotide
Includes the deletion, insertion, or substitution of ONE nucleotide in a gene
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Point Mutation Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene
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Frameshift Mutation Inserting or deleting one or more nucleotides
Changes the “reading frame” like changing a sentence Proteins built incorrectly
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Frameshift Mutation Original: The fat cat ate the wee rat.
Frame Shift (“a” added): The fat caa tet hew eer at.
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Amino Acid Sequence Changed
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Gene Mutation Animation
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FYI
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Normal Male 2n = 46
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Normal Female 2n = 46
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Male, Trisomy 21 (Down’s) 2n = 47
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Female Down’s Syndrome
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Klinefelter’s Syndrome
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Turner’s Syndrome 2n = 45
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