mutation rates vary considerably among species

1
mutation rates vary considerably among species
2
mutation rates vary considerably among genes
within a species
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most mutations are deleterious WHY??
if all mechanisms were nearly perfect any
change would be detrimental.
Maybe
50 chance of improvement
Best place
4
most mutations are deleterious WHY??
if all mechanisms were nearly perfect any
change would be detrimental.
Maybe
suppose two dimensions
chance of improvement lt 50
with many more dimensions the chance of
improvement goes to zero
5
most mutations are only slightly deleterious
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(No Transcript)
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Origins of new genes
duplications -- unequal crossing
over may involve entire gene or partial
gene
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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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deletion
ancestral trypsinogen gene
new gene with two exons
two duplications of sequence ecoding the first
three amino acids (Thr-Ala-Ala)
addition of spacer sequence

multiple duplication events
(from Graur Li 2000)
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ancestral trypsinogen gene
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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What produces homogeneous tandem arrays ?
repeated duplication of one gene
spread of a mutation via gene conversion
or unequal crossing over
concerted evolution tendency of members
of a gene family to evolve interdependently
fixation of beneficial mutations
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Concerted evolution by gene conversion








































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concerted evolution by unequal crossing over
initial homogenization by duplication