Welcome back to IB 150...

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Welcome back to IB 150...
Vocero-Akbani et al. 1996. Mapping human
telomere regions with YAC and P1 clones
Chromosome specific markers for 27 telomeres
including 149 STSs and 24 polymorphisms for 14
proterminal regions. Genomics 36492-506 .
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Exam Announcements

• Exam is Thursday February 23 from 7-9 PM
• Details www.life.uiuc.edu/ib/150/Examoneinfo.html
• Exam is multiple choice, 72 questions
• Conflict Exam - requests to take the conflict
  exam must be made to Tracey Hickox,
  hickox_at_life.uiuc.edu, not later than 5 PM on
  Friday

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Exam Location

• 1 IF YOUR TA IS CHRISTINE or JENNY GO TO 112
  GREGORY HALL
• 2 IF YOUR TA IS BETH or EMILY GO TO 141 WOHLERS
  HALL
• 3 IF YOUR TA IS HELEN or BEN GO TO 114 DAVID
  KINLEY HALL
• 4 IF YOUR TA IS MAHESHI GO TO 23 PSYCHOLOGY
  BUILDING

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5 PM, Tuesday the 21st 228 Natural History
Building
Dr. Pennock - witness at the recent trial in
Dover, PA over teaching of Intelligent Design
Presented by UIUC Darwin Club
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Lecture 13 Microevolution
Assigned Readings Ch. 23 (rest of chapter)
Predicting genotype frequencies from allele
frequencies - the Hardy-Weingberg equilibium
random mating, inheritance and evolution Natural
Selection The evolution of HIV and
other diseases Putting genetic drift and
mutation together allele gain and lossneutral
evolution
Practical Uses of Population Genetics
Forensic genetics, microsatellites
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Last time.

• Description of the genetics of a population
• Forces that can cause allele frequencies to
  change
• But what about inheritance itself - can it cause
  evolution (major issue 100 years ago)

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Mathematical proof that genetics does not cause
evolution...
Relationships between alleles and genotypes are
understandable in terms of population genetics
Are there simple rules for relating genotype
frequencies to allele frequencies? Can we
predict genotype frequencies from allele
frequencies?
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Yes!
Hardy-Weinberg equations for population with 2
alleles at a locus (but only works if one assumes
random mating)
p q 1
Generation 1
Frequency of A allele
Frequency of a allele
p2 2 pq q2 1
Generation 2
Frequency of AA genotype
Frequency of Aa genotype
Frequency of aa genotype
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A Hardy-Weinberg Equilibrium is just like a
Punnett square except for a population rather
than a single pair cross.
Sperm with allele A p
Sperm with allele a q
pq Aa
p2 AA
Ova with allele A p
pq Aa
q2 aa
Ova with allele a q
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Fig. 23.5
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But what does this mean?

• It means that unless an evolutionary force is
  acting on a population the allele and genotype
  frequencies will remain constant forever
• This never really happens but is a good
  approximation in some cases
• In others it is a null hypothesis

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If the genotype frequencies can be predicted
perfectly from the allele frequencies, the
population is said to be in a Hardy-Weinberg
Equilibrium. A perfect Hardy-Weinberg
equilibrium is seen only if there is no genetic
drift, no mutation, no natural selection, etc.,
but it is in fact rather robust to violations of
these conditions.
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Using H-W to determine frequencies of carriers in
a population (must assume at least approximately
random mating)
Phenylketonuria recessive Mendelian
trait 1/10,000 children born in the US have the
disease What proportion of the population are
carriers?
q2 0.0001
q 0.01 p 0.99
2 of the population are carriers
2pq 0.0198
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The Hardy-Weinberg Equilibrium is important
because 1. It helps us understand human genetic
diseases - (e.g., why are carriers so much more
common than affected people?) 2. Its robust to
many assumptions. 3. Its fundamental to a lot
of population genetics. 4. Its used in forensic
genetics
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Selection on Genes

• A fourth evolutionary force - natural selection
• At the genetic level selection acts by conferring
  different fitnesses to different alleles.
• Fitness is the contribution that the allele makes
  towards the individuals success at survival and
  reproduction

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An example In this example the red flowers are
visited twice as often by pollinators as the pink
flowers while the white flowers are not visited
at all. What happens?
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The fitness values of the three genotypes will be
0, 1, and 2
We can tally up the number of offspring
total
3
10
5
2
2 X 2 4
3 X 0 0
5 X 1 5
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This changes the allele frequencies in the next
generation

• White allele (q) 5/18 0.28
• Red allele (p) 13/18 0.72
• Selection has caused an increase in the frequency
  of the red allele.

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Natural Selection is Important in Medicine

• HIV - what does it do and why is it so hard to
  find a cure or a vaccine?
• Biology of the virus
• Host/pathogen relationship and selection on
  virulence
• Rapid mutation rate
• Evolution of resistance

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The HIV Virus
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Biology of HIV

• An RNA retrovirus - no metabolism of its own.
• Injects RNA and reverse transcriptase into host
• Makes HIV DNA that gets incorporated into host
  cell - makes more HIV

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(No Transcript)
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Mutation in HIV

• Reverse transcriptase is error-prone
• No mechanism for correcting errors
• HIV has an extremely high mutation rate

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Why does HIV kill people?

• HIV attacks cells associated with the immune
  system
• Higher the rate of reproduction of HIV, the more
  virulent the disease
• Virulence may be an evolved trait

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Succession in Reproduction

• HIV needsto get into new hosts
• If transfer to new hosts is common then a rapid
  rate of reproduction is favored
• If transfer to new hosts is rare then a slower
  rate of reproduction is favored

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Evolution of Resistance

• New HIV drugs often start off working well
• Generally decline in effectiveness over time
• Rapid mutation rate and strong selection rapid
  evolution of resistance

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Some Specific Examples

• Gene Duplication
• The Interaction of Drift and Mutation - Neutral
  Evolution
• Forensics and the Use Population Genetics

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Beside point mutations, there are other types of
mutations that can occur - such as gene
duplications that add extra copies of genes.
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Duplications, continued

• These duplications can occur in the context of
  speciation
• Or they can allow the evolution of new gene
  functions - increase complexity

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Neutral Evolution

• Combination of the effects of drift and mutation
• Molecular changes in genes that do not affect
  fitness

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What can happen to a new mutation? (3 different
ones graphed)
1.0
p
0.0
TIME
Mutant 1
Mutant 2
Mutant 3
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But even if an allele is fixed by drift, there
will always be a new one...
1.0
p
0.0
TIME
Mutant 3
Mutant 4
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Start - 1 fixed allele
Allele frequency
The grand view of the combined effects of drift
and mutation - new alleles arise by mutation, may
go extinct immediately or increase. But all
alleles go extinct eventually. Thus, neutral
evolution is inevitable!
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Consequences of Neutral Evolution

• Neutral changes accumulate
• Rate of change depends on rate of mutation
• Related individuals or related species have
  similar alleles

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Microsatellite variation - differing numbers of
short DNA repeats - an actual example with a
pedigree.
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Genotypes frequencies and microsatellite
variation - the more alleles, the more genotypes,
and the lower the frequency will be for each.
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Lecture 13 Microevolution
Assigned Readings Ch. 23 (rest of chapter)
Predicting genotype frequencies from allele
frequencies - the Hardy-Weingberg equilibium
random mating, inheritance and evolution Natural
Selection The evolution of HIV and
other diseases Putting genetic drift and
mutation together allele gain and loss
neutral evolution
Practical Uses of Population Genetics
Forensic genetics, microsatellites