BIO2008: Lecture 6

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  • Created on: 11-05-14 10:36
why may some populations be continuously small for a relatively long period of time?
limited resources, fragmentation
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what is the founder effect?
a new population is founded by few individuals, new population has variation present in those few individuals < in source population
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what are bottlenecks in populations?
where the population size is reduced dramatically?
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what are regular event bottlenecks?
seasonal variation in resources resulting in death of many individuals in resource poor times
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what are irregular random event bottlenecks?
e.g. storms or disease destroying a large number of individuals
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what is a sustained pressure bottleneck?
habitat destruction by humans or loss of individuals through hunting or introduced predators
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What is a metapopulation (clue: a way that populations can remained small for long time)
a group of spatially separated populations of the same species which interact at some level or 'a collection of interacting populations of the same species'
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what 2 effects can the founder effect have?
1) Loss of variation: An allele may be lost, population may be genetically monomorphic 2) Diversification through drift: In a small sample: frequencies of allele may differ from the parental population: high frequencies of otherwise rare alleles
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what is an example of the founder effect?
The frequency of Ellis-van Creveld syndrome in the Amish population of Pennsylvania- many times more common in the Amish population than in the general American population.
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what is the form of dwarfism of Ellis-van Creveld syndrome?
involves short stature, polydactyly (extra fingers or toes), abnormalities of the nails and teeth, and, in about half of individuals, a hole between the two upper chambers of the heart.
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Each distinct population in a metapopulation may be referred to as what?
a subpopulation, a local population, or simply as a population
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what is a example of a metapopulation?
mountain sheep- Ovis canadensis
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describe te attributes of a metapopulation?
1) Naturally or created as a result of human actions 2) Patchy distribution of habitats 3) Migration may be very low: genetic problems as in small populations
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Small populations – low levels of variation, because strong effect of what?
Random genetic drift
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Metapopulations have (blank) levels of variation within subpopulations?
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what is genetic drift?
random events that remove members of the population unrelated to the individuals fitness. Chance process.
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Small populations lead to loss of diversity. Why is this loss of genetic diversity important?
Loss of genetic variation leads to: 1) Inbreeding depression (recessive lethals become homozygous) 2) Inability to adapt to a changing environment or cope with new diseases- Genetic variation is the raw material for evolution
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what is an example of the impact of low diversity on reproduction?
The frequency of sperm abnormalities is very high in cheetahs
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Decline of genetic diversity since 1969 is a result of what?
Perhaps linked to a falling reproductive rate- structural deformities in more than half the sperm of each male tested, strong evidence of inbreeding.
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If cheetahs underwent a severe bottleneck 10 000 years ago, why did they not go extinct over the last 10 000 years?
A new disease may come along a few years after a bottleneck, wiping out the small, remnant, non-diverse population, or it may take 1000s of years before an environmental change comes along that elephant seals or cheetahs are incapable of coping with
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what has allowed us to know more about the extent of variation in natural populations + or about relationships of closely related species or subspecies?
PCR technique
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what are essential to ensure at risk populations are identified and that extinction of such populations via loss of variation is prevented?
Genetic surveys
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what is the genetic effective population size (Ne)?
the size of a genetically ‘ideal’ population, which has the same rate of loss of heterozygosity as an actual, non-ideal, wild population.
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what is an ideal population?
random mating, equal sex ratios, no selection, equal contribution to next generation, non-overlapping generations
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what is lost over time in a finite population, and even more if non-ideal (deviation from random mating, non-equal contribution to next generation, skewed sex ratios etc)?
genetic variation
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What is Ne affected by?
the mating structure of the population in each generation, and the variation in population size over time. 
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Any deviation from random mating (polygamy, etc.) will reduce or increase Ne relative to N?
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what is formula for Ne in a diploid species?
Ne = 4 (Nm)(Nf)/(Nm + Nf), Nm and Nf are numbers of breeding males and females
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Sex ratio will be skewed in dominance systems, what does this mean?
one or a few dominant males inseminate/fertilise all the females.
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what are harem structures?
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Ne decreases or increases rapidly as breeding sex ratio becomes more biased towards one sex?
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Ne of a eusocial insect with one queen and many drones is relatively low compared to solitary insects?
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in eusocial (colonial) insects e.g. ants, bees, what is the ratio of males/females?
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Thus eusocial species are expected to have Ne much less or more than N?
Much less
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what is Haplodiploidy?
Sex determining mechanism by which males develop from unfertilized eggs
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in haploploidy, how are males and females produced?
Males are haploid and produced by parthenogenesis and females are produced by the fusion of reduced eggs and sperm
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Does haploploidy mean a lower or higher Ne than in diploid species?
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does a haplodiploid has fewer or more copies of a given gene?
fewer- only 1 copy in males- in a population than does a diploid
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If random sampling of gametes is assumed what is the effective population size for diploids?
Ne (diploid) = 4(Nf x Nm)/(Nf + Nm )
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what is it for haplodiploid?
= 9(Nf x Nm)/(2Nf + 4Nm)
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With equal sex ratios what is the effective population size for haplodiploids in relation to diploids?
effective population size for haploploids is 3/4 that diploids
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which have less genetic variation, diploid, eusocial haplodiploid or solitary haplodiploid insects?
diploids have the most genetic variation, then eusocial have less genetic variation than solitary haplodiploid insects
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what impact does asexual reproduction have on genetic diversity?
lower genetic diversity
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what impact does positive assortative mating and self fertilisation have on heterozygosity?
Decreases heterozygosity
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what impact does negative assortative mating have on heterozygosity?
Increases heterozygosity
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whats impact does dominance and sociality have on genetic diversity?
decreases genetic variation through decreasing effective population size
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what does the inbreeding mating system do to variation within and between populations?
more variation between populations, less within populations- High Fst value
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hat does the outcrossing mating system do to variation within and between populations?
a lot of variation present within populations and therefore relatively less between populations – low FST value
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Card 2


what is the founder effect?


a new population is founded by few individuals, new population has variation present in those few individuals < in source population

Card 3


what are bottlenecks in populations?


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Card 4


what are regular event bottlenecks?


Preview of the front of card 4

Card 5


what are irregular random event bottlenecks?


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