new alleles arise from changes in DNA sequence

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new alleles arise from changes in DNA sequence
point mutations deletions insertions transposition
inversion or translocation breakpoints
frameshift mutations
point mutations may either be synonymous
substitutions -- no change in amino acid
identity replacement substitutions --
changed amino acid
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60-70 of mutations are transitions
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Basic
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Basic
Acidic
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most mutations are deleterious -- C. elegans
(Vassilieva et al. 2000)
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most mutations are only slightly deleterious
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Origins of new genes
duplications -- unequal crossing
over may involve entire gene or partial
gene
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Lynch Conery 2000
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fate of gene duplications pseudogene
invariant repeats - rRNA, tRNA, histones
variant repeats gene familes - globin, growth
factors novel function - thrombin (blood
clotting) trypsin (digestive enzyme)
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New genes via internal duplications antifreeze
glycoprotein in Antarctic Toothfish
(Dissostichus mawsoni)
waters of the Antarctic Ocean
-1.9oC most fish freeze at -1.0oC to 0.7oC
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deletion
ancestral trypsinogen gene
Start
Original stop codon
new gene with two exons
duplications of sequence encoding the first
three amino acids (Thr-Ala-Ala) and
addition of spacer sequence
internal duplications and addition of intron
sequence
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antifreeze glycoprotein gene
(from Graur Li 2000)
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New genes via exon shuffling tissue plasminogen
activator evolves from four unrelated
genes
protease
kringle (plasminogen)
epidermal growth factor
fibronectin type-1
(from Graur Li 2000)
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some genes occur as highly repeated tandem arrays
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Concerted evolution by gene conversion








































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concerted evolution by unequal crossing over
initial homogenization by duplication
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new alleles are produced by mutation most
mutations are slightly deleterious duplication
is the most important mechanism for producing
new genes concerted evolution maintains sequence
similarity in certain gene families such as rRNA
genes