dna mutations
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DNA Mutations. Chapter 12.4. Mutation. Mutation : Any change in a gene is a mutation. Substances that cause a mutation are called mutagens. Mutations can also happen spontaneously. Point Mutation. A change in one nucleotide - PowerPoint PPT PresentationTRANSCRIPT
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DNA Mutations
Chapter 12.4
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Mutation• Mutation: Any change in a gene is a
mutation.• Substances that cause a mutation are
called mutagens. • Mutations can also happen spontaneously.
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Point Mutation• A change in one nucleotide
• Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.
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Point Mutation• Base Substitution - One nucleotide is
replaced with another nucleotide.
ACC CUA GGC AUC AU ACC UUA GGC AUC AU
“C” is substituted with “U”
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Redundant Systems• Sometimes these mutations have no
effect!! Ex. The codons of UCU, UCC, UCA, & UCG all code for the amino acid Serine. Any substitution in the third base of the codon has no effect.
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• However, a substitution in the first or the second base of the codon, changes the code for the amino acid.
• UUU codon is for phenylalanine• UCU codon is for serine• CUU codon is for leucine
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Frameshift Mutations• Either the insertion or a deletion of a
nucleotide which results in a shift in the code and mistakes from the point of mutation on.
• Original The fat cat ate the wee rat.
• Frame Shift The fat caa tet hew eer at.
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Somatic Cell mutations
•Mutations happen in all organisms, if it happens in a somatic cell then only the individual is affected.
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Meiosis Mutations
•If it happens in a gamete then the mutation is passed on to the offspring.
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Meiosis Mutations
• Mistakes during meiosis: Mistakes during meiosis, such as non-disjunction, can result in three chromosomes instead of a pair (trisomy) or more than three (polyploidy).
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Down’s Syndrome• Trisomy in humans can result in birth
defects such as trisomy 21, or Down’s syndrome.
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Quick Review• Point mutations
occur as a result of a change in one nucleotide.
• The 2 basic types of point mutations are base substitutions and frame shift.
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Quick Review• Substitution
mutations are the result of one nucleotide being replaced by another. This results in one amino acid being incorrectly coded.
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Quick Review• Frame shift
mutations are the result of either a deletion or an insertion of a nucleotide. This results in a mistake in all the triplet codes from the mutation on.
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Gene Mutations• Gene Mutations occur as a result of
changes in chromosomal fragments. There are four basic types:
• 1. Translocation• 2. Inversion• 3. Insertion• 4. Deletion
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Gene Mutations1.Translocation
s - When part of one chromosome breaks off and is added to a different chromosome.
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Gene Mutations2. Inversion –
When part of a chromosome breaks out and is reinserted backwards.
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Gene Mutations
3. Insertion When part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome.
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Gene Mutations
4. Deletion
When part of a chromosome is left out.
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Mutations & Evolution
• Mutations that have a negative effect usually result in the loss of that mutation due to the law of the survival of the fittest.
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Mutation & Evolution• However, there are
times that the mutations are beneficial and result in the evolution of the species and increased variation in the population.
• We’ll learn much more about this next unit!!!
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