Population Genetics

1
Population Genetics

• The study of genetic variation and its causes in
  population

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Suggestion to do well in this class Attend
every lab session. Give your undivided
attention. Ask the TA to repeat himself.
Review the power-point presentations before the
quiz. Hand your assignment in due time. Do
your best with the lab. reports
3
Announcements

• Cedo field trip.
• preceptor program
• Home assignment include game 1, 2, and questions
  1, 3 and 4
• on page 12
• There will be a quiz (8 points) on Thursday,
  February 3th.
• The questions will cover materials from the
  population
• genetics lab and the classification and
  phylogeny lab.

4
Population Genetics

• Evolution
• Mechanisms of evolution
• How to prove it
• How to measure evolution

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Evolution

• Population is a group of individuals that coexist
  in certain place at the same time and capable of
  interbreeding with one another
• Evolution is change over time in the traits of a
  population
• Phenotype is the observable properties of an
  organism.
• Gene is piece of DNA that codes for a protein
• Alleles are different forms of a gene

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Evolution

• Genotype is the genetic composition the governs
• a trait (AA, Aa, aa)
• Evolution is change of the allele frequencies
  over time.
• Dominant allele, determine the phenotype of
• heterozygous individuals.
• Recessive allele, shows its phenotype only in
• homozygous individuals

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Forces of evolution

• Natural selection
• advantage in survival and reproduction.
• Mutations.
• random changes in nucleotide sequence.
• Migration (gene flow).
• new individuals are introduce to the population.
• Non-random mating.
• possession or absence of certain phenotype.
• Genetic drift.
• random changes (allele fixation in small
  population).

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Natural selection
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Genetic drift
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Genetic drift

• Its effect is clear in small populations
• These populations lose genetic variability
  rapidly.
• alleles drift to fixation.
• http//darwin.eeb.uconn.edu/simulations/drift.htm
  l.

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Gene flow
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Applied aspects of population genetics
Cystic fibrosis
Cystic Fibrosis (CF) is the most common AR
(autosomal recessive) disorder found in
Caucasians with an estimated incidence of 1 in
2500 in newborns of European ancestry. About 1
in 25 persons of European ancestry is a
carrier.CF especially affects the respiratory
and digestive systems. The CF gene was identified
in 1989. The average life expectancy of a person
with CF is now at 30 years, due to advances in
medical care.
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Evolution
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How to prove that evolution occur

• Hardy-weinberg theory (equilibrium)
• A population that is not changing genetically
  from generation to generation.(null hypothesis)
• Essential assumptions
• 1-Mating is random
• 2-Population size is very large (no effect for
  genetic drift)
• 3-Mutations can be ignored
• 4-Natural selection has no effect
• 5-No migration

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Hardy-weinberg theory (equilibrium)
sperm
A
a
AA
Aa
A
Punnett square
eggs
aa
Aa
a
Frequency of event actual number of occurrence
total number of
events
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Hardy-weinberg theory (equilibrium)

• Allele frequency number of occurrence of that
  allele
• total number
  of alleles in the population
• Genotype frequency number of occurrence of that
  genotype
• total
  number of the population
• or product of its alleles frequency p q
• Note frequency is just another way to express
  (absolute)numbers. It is just the decimal
  fraction
• p q 1
• p2 2pq q2 1

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How to measure evolution

• Calculate allele and genotype frequencies in
  each generation
• and compare it to the previous one.
• are differences in genotype frequency from
  generation
• to generation evident? Are we sure that these
  differences
• have not happened due chance alone?
• Significance of the difference in frequency
• chi-square analysis ( X2 ) P.200
• X2 ? (O E )2
• E
• ? X2 0
• it is hardy-weinberg equilibrium ( H0 or null
  hypothesis)
• The higher the value of X2, than that obtained by
  chance,
• the more likely to be significant

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How to measure evolution

• ? Degree of freedom number of categories that
  are free to
• vary
  indepenantly .
• df total number of categories - 1

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Questions
1a- population in game 2 1b- for game 2, we have
high confidence because the probability of
sampling error were less than 5 . For game 1,
vice versa.. 1c- population in game 1 1d-
population in game 2 because evolutionary force
(natural selection) was acting in the
population. 3a- by natural selection 3b-heterozygo
us individuals 4- aa 0.7x 0.70.49
AA0.3x0.30.09 Aa0.3x0.70.21
0.21x20.42