Download What can affect the effective population size? Genetic bottlenecks

1) What can affect the effective population size?
a) Genetic bottlenecks
b) Unequal number of males & females
c) Population size through generations
d) Variance in reproductive success
e) Founder effect
f) All the above
2) Under which circumstance is gene flow stronger than genetic drift?
a) Ne*m = 0
b) Ne*m = 1
c) Ne*m = 11
3) What situation is present when Ne*s = 8 ?
a) One allele has a selective advantage over another
b) Selection is stronger than drift
c) Drift is stronger than selection
d) Drift & selection are in equilibrium
4) How does functional constraint affect the neutral theory of molecular evolution?
a) Most mutations are harmful and removed by purifying selection
b) Some mutations are neutral and accumulate due to genetic drift
c) Few mutations are positive and may become fixed due to natural selection
d) The specialization of a molecule affects how it may be impacted by mutations
e) Evolution due to neutral mutations & genetic drift
5) What is an example of segregational load?
a) Cheetahs having low genetic diversity
b) Male elephant seals have a harem & therefore the effective population size is lower than n
c) Decreased fitness of homozygotes with the sickle cell allele
d) The view of Mendelian geneticists on the great wrinkled pea debate of 2003
6) Write two questions you have on the paper
Effective population size : Number of individuals that are reproducing per generation sets rate of
genetic drift
Harmonic mean is used to calculate population size through generations
Unequal number of males & females can impact
Northern elephant seal males have a harem, males mate with many females
Large variance in reproductive success (some organisms don’t mate)
Genetic bottleneck is when the population goes through a contraction and affects genetic diversity
Cheetahs
Founder effect is a bottleneck caused by migration & population has low diversity
Gene flow vs drift
Ne is effective population size, m is number of individuals migrating
Ne * m = number of reproducing migrants
Ne * m > 1 flow overrides drift (1 migrant per generation)
Ne * m < 1 drift overrides flow
Genetic drift vs selection
S is selective advantage of one allele over one another
Ne * s = the selective advantage of an allele in the population
If any allele has high selection coefficient, selection overrides drift
Ne * s > 10 selection overrides drift
1 < Ne * s <10 equilibrium
Ne * s < 1 drift overrides selection
c-value paradox : there is no relationship between organism complexity and c-value
c-value is amount of DNA in organism
isochore repeating patterns in DNA which are found in warm-blooded critters, not ectotherms
G & C are heavy, A & T are light
Molecular evolution can be decoupled from morphological evolution
Humans & chimps are genetically similar but morphologically distinct
Neutral theory of molecular evolution
Most mutations are harmful and removed by purifying selection
Some mutations are neutral and accumulate by genetic drift
Very rarely, beneficial mutations are fixed by positive selection
Rate of evolution of molecule is determined by its degree of functional constraint
Functional constraint: how fine-tuned a molecule is for its task
The more tuned, the less evolution & vice versa
Most of molecular evolution is due to neutral mutations & genetic drift
Neutralist-selectionst controversy is value of neutral vs beneficial mutations
Starch electrophoresis disproved both views
Many genes disproved classical (naturalists)
High number of heterozygotes disproved mendelians (balanced)
Segregational load is the cost of balancing selection, many recessive homozygotes are created
Therefor, balancing selection is rare
Tishkoff, S.A., Reed, F.A., Ranciaro, A., Voight, B.F., Babbitt, C.C., Silverman, J.S., Powell, K.,
Mortensen, H.M., Hirbo, J.B., Osman, M. and Ibrahim, M., 2007. Convergent adaptation of human lactase
persistence in Africa and Europe. Nature genetics, 39(1), pp.31-40.
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A selective sweep for lactose tolerance has occurred over the last 7,000 years
Decrease of lactose enzyme in humans after weaning prevents ability to digest lactose
o Present in small intestine
Individuals descended from cattle domesticating ancestors have ‘lactose persistence’ trait
Dominant trait
Allele arose ~2,000-20,000 years ago in Europeans
o Lactose persistence is high in Europeans, medium in southern Europe & Middle East,
and low in Asian & African populations
Lactose persistence evolved independently in most African populations
o This paper looks at genotype-phenotype associations in 470 East African individuals
o Determined SNP’s associated with lactose-tolerance, which was determined by blood
glucose test after digestion of lactose
Time since selection began for the allele is based on the increased frequency of tails on either
side of the beneficial mutation
o Haplotype is inherited chromosomes from parent
o If selection is recent, will have high and narrow tails
 random linkage disequilibrium has not had enough time to decrease tails