Evolution

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Evolution Mon, Wed Fri 200 250
pm Spring Semester 2006
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Evolution 1 2006 Spring
Changes in gene frequency
What causes changes in the allele frequency?
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Evolution 2 2006 Spring
Changes in gene frequency
Important processes -gt mutations introduce
new variations -gt selection
improves/diminishes the chances that new
variations increase their gene frequency
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Evolution 3 2006 Spring
Changes in gene frequency

• 3 types of mutations
• No effect (silent mutations)
• Lethal or negative effect
• Selective advantage

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Evolution 4 2006 Spring
Changes in gene frequency
Mere appearance of a new trait is no guarantee
that it will persist new carrier -gt may or may
not survive -gt may or may not reproduce
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Evolution 5 2006 Spring
Changes in gene frequency
Fisher calculated New mutations have a 33
chance of being lost within one generation New
mutations have a 95 chance of being lost after
30 generations
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Evolution 6 2006 Spring
Changes in gene frequency
Mutations frequency -gt the more frequently a
specific mutation happens the higher the
likelihood of persistence in the gene pool
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Evolution 7 2006 Spring
Changes in gene frequency
Selection Phenotypes differ in viability and
fertility gt influences their genotype
frequency! fitness ( selective value,
adaptive value)
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Evolution 8 2006 Spring
Changes in gene frequency
Fitness -gt Individual that have more offspring
than others -gt Individuals that contribute
more to future generations than others
are fitter than others.
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Evolution 9 2006 Spring
Changes in gene frequency
Fitness gt Is the number of an individuals
descendents that influence the heritable
characteristics of the population. gt Is
measured by the proportionate contribution
an individual makes to future generations
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Evolution 10 2006 Spring
Selection in haploid vs. diploid organisms
What is the difference? Which one has more
impact?
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Evolution 11 2006 Spring
Selection in haploid vs. diploid organisms
Haploid -gt effect is more rapid and direct -gt
deleterious recessive alleles can not be
hidden Diploid -gt deleterious recessive alleles
can be hidden in heterozygous genotypes -gt
depends on the degree of dominance
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Evolution 12 2006 Spring
Selection in haploid vs. diploid organisms
Usually deleterious traits are recessive and
therefore mostly hidden Carrier -gt
heterozygous Carrying recessive trait without
phenotypic expression
Dd Joshua Lambert
Dd Abigail Linnell
D_ JohnEddy
?
D_ HepzibahDaggett
?
D_ Abigail Lambert
Dd Elizabeth Eddy
?
dd JonathanLambert
dd
Dd
Dd
Dd
dd
Dd
Dd
Female
Male
Deaf
Hearing
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Evolution 13 2006 Spring
Selection in haploid vs. diploid organisms
Some disorders are caused by dominant
alleles Examples Achondroplasia
Alzheimers disease -gt not threatening -gt
strike after reproductive phase
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Evolution 14 2006 Spring
Selection and polymorphism
Polymorphism at least two alleles are
present one allele has at least 1 frequency
compared to the other Balanced polymorphism
persistance of different genotypes -gt
preservation of genetic variability
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Evolution 15 2006 Spring
Selection and polymorphism
Individual homozygousfor sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Abnormal hemoglobin crystallizes,causing red
blood cells to become sickle-shaped
Example Sickle cell anemia Recessive
allele Heterozygous individuals have a higher
chance of surviving malaria infections
Sickle cells
Clumping of cells and clogging of small blood
vessels
Accumulation ofsickled cells in spleen
Breakdown of red blood cells
Physical weakness
Heart failure
Pain and fever
Brain damage
Damage to other organs
Spleen damage
Anemia
Pneumonia and other infections
Impaired mental function
Kidney failure
Rheumatism
Paralysis
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Evolution 16 2006 Spring
Selection and polymorphism

• Relationship between geographical distributions
  of
• Malaria
• Sickle cell anemia

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Evolution 17 2006 Spring
Selection and polymorphism
gt Even lethal recessive alleles remain in
the population if they confer only a small
selective advantage!