Download 122 lec 12 mut evol

Introduction to mutation
• Point mutations (Ch. 17)
– Substitutions
– Insertions or deletions
• Chromosomal mutations (Ch. 15,
pp. 285-7)
– Chromosome structure
– Chromosome number
Point mutations
Substitutions
• silent mutations- no change in amino
acid produced
• missense mutations
– change in a single amino acid
– may or may not matter
• nonsense mutations
– Codon becomes stop codon
– Loss of protein can be catastrophic
Figure 17.4 The dictionary of the genetic code
Figure 17.24 Silent substitution
Figure 17.24 Missense substitution
Figure 17.23 The molecular basis of sickle-cell disease: a point mutation
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Figure 17.24 nonsense substitution
Base-pair insertions or deletions
• Generally causes frameshift, or
change in reading frame
• This results in many wrong
amino acids or change to a stop
codon
• With three bases, reading frame
can be restored
Figure 17.24 Categories and consequences of point mutations: Base-pair
insertion or deletion
Figure 17.24 Categories and consequences of point mutations: Base-pair
insertion or deletion
Figure 17.24 deletion without frameshift
Significance of point mutations
• Reduction or loss of protein function
– Substitutions (missense, nonsense)
– Insertions or deletions
• Little or no change
– Silent- no effect
– Missense- may not affect protein
– A few insertions or deletions
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Introduction to mutation
• Point mutations (Ch. 17)
– Substitutions
– Insertions or deletions
• Chromosomal mutations (Ch. 15,
pp. 285-7)
– Chromosome structure
– Chromosome number
Types of mutations
in chromosome structure
• Deletion- loss of genes
• Duplication- additional copies of genes
• Inversion- order of genes reversed
• Reciprocal translocation- crossing over
between non-homologues
Figure 15.13 Alterations of chromosome structure
Deletions
–can lose gene products
–may be lethal
Figure 24.23 Hox mutations and the origin of vertebrates
Duplication
• can change phenotype
• gene may evolve a new function
• Multiple duplications may lead to
‘gene families’
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Inversion and translocation
Mutations in chromosome number
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No loss or gain of genes
changes linkage relationships
problems for heterozygotes
Populations with different mutations can
not interbreed
Figure 15.11 Meiotic nondisjunction
Consequences of mutations
in chromosome number
• aneuploidy
– fatal if missing genetic information
– disadvantageous if excess of
information
• polyploidy
– In animals usually fatal
– plants commonly experience this and it
seems to cause plant speciation
• Aneuploidy- one chromosome
extra in one gamete, one too few
in other gamete
• Polyploidy- diploid gamete
formed
Figure 24.13 Sympatric speciation by autopolyploidy in plants
Evolutionary significance of
chromosomal mutations
• disadvantageous in many cases
– Loss or excess of important proteins
– Reduction of heterozygote fertility
• Little effect on phenotype but
reproductive isolation between
‘chromosomal races’
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