BIO2008: Lecture 11

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  • Created by: LMoney
  • Created on: 11-05-14 14:06
how are polymorphisms maintained?
1) mutation 2) migration 3) selection 4) drift
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what is balancing selection?
Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies above that of gene mutation- maintains variation in pop.
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what are clines?
ecotypes or forms of species that exhibit gradual phenotypic and/or genetic differences over a geographical area, typically as a result of environmental heterogeneity
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what causes balancing selection?
1) Heterogeneity in environment and clines (spatial, time) 2) Heterozygote superiority, over dominance 3) Frequency dependent selection 4) ‘Supergenes’
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what is overdominance?
heterozygote advantage, wherein heterozygous individuals have a higher fitness than homozygous individuals.
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what is frequency dependent selection?
an evolutionary process where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population- the fitness of a phenotype increases as it becomes more common
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what is a supergene?
a group of neighbouring genes on a chromosome which are inherited together because of close genetic linkage and are functionally related in an evolutionary sense, although they are rarely co-regulated genetically
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Would a mosaic of habitats and different environments increase diversity?
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two or more selection pressures maintain what?
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which genetic blood disorder shows heterozygote advantage and over dominance?
sickle cell anemia
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which species of snail exhibits multiple selection factors and frequency dependent selection?
Cepaea nemoralis, grove snail
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what is cyanogenesis in clovers an example of?
multiple selection factors
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what is negative frequency-dependent selection?
In negative frequency-dependent selection, the common forms of a species are preyed on more than the rarer forms and this allows the rare morphs to have a selective advantage in the population- selection coefficients are not common
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what is an example of frequency stable selection giving rise to stable polymorphism?
the cichlid 'Perissodus microlepis'- a scale eating fish in lake Tanganyika
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what phenotypes are there in this species?
Distorted mouth parts: Right- and left-mouthed fish attack from different sides
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which side do most fish attack from? i.e. which is dominant?
Right is dominant
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what is self-incompatibility in plants?
a general name for several genetic mechanisms in angiosperms, which prevent self-fertilization and thus encourage outcrossing
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How does self-incompatibility work?
In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant, the process of pollen germination, pollen tube growth, ovule fertilization, and embryo development is halted at one of its stages
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is there frequency dependent selection amongst plants?
there is negative frequency selection among plants for an unknown reason- possibly 1) Different usage of resources 2) Diseases
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which mode of natural selection is most important in maintaining genetic variation at single-loci?
1) negative frequency-dependent selection 2) heterogeneity and clinical variation (time and space)
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what is another name for coadapted linkage groups?
supergenes- another factor maintaining variation- Genes closely linked on the same chromosome - do not segregate independently and rarely recombine
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alleles are in (blank) disequilibrium
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what are some examples of 'super genes'?
1) ‘thrum’ chromosome in pin and thrum Primula 2) Mimicry in butterflies 3) Cepea nemoralis
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Does primula exhibit negative or positive assortative mating?
Negative assortative mating
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what is bayesian mimicry?
a form of mimicry typified by a situation where a harmless species has evolved to imitate the warning signals of a harmful species directed at a common predator. It is named after the English naturalist Henry Walter Bates, after his work in the rain
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what is aposematism?
perhaps most commonly known in the context of warning coloration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators
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which type of snail exhibits Colour and banding polymorphisms?
Capaea nemoralis
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Colour and banding genes are linked to form what?
a coadapted linkage group
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what is the order of dominance for Capaea nemoralis?
brown > pink > yellow
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what is the dominance in the banding?
unbanded > banded
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what other type of selection does Capaea show?
Frequency dependent selection
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what is the most important predator of Cepaea?
Song thrush
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which Cepaea phenotype would be most common in forest?
Brown, least conspicuous
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Which Cepea type would be most common in long grassland?
Yellow banded
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which phenotype of snail do song thrushes target on the Northumberland coats?
yellow 5 banded, perhaps because this is predominant type in Norway
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Coadapted linkage groups partly explain what?
polymorphisms- Because colour and banding are linked, certain linkage combinations are selected together
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If observed numbers are significantly commoner or rarer than expected this may be due to what?
linkage disequilibrium
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are yellow and pink banded more common or more rare than expected?
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are yellow unbounded and pink banded more common or more rare than expected?
Yellow unbanded and pink banded are rarer than expected
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do Cepaea shell genes ever go to fixation?
no- Almost all populations of Cepaea remain polymorphic for all three genes- directional selection not strong enough to cause fixation
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define clines?
Environmental differences in selection
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in clover where are the cyanogenic glycosides linamarin and lotaustralin in white clover? (Trifolium repens)
in vacuole
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where is the Glycosidase linamarase located in the cell?
membrane bound
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what happens if the tissue of a clover is damaged?
production of HCN and ketone- HCN inhibits terminal oxidase, kills all living things at >20mg/100 g
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is the glycoside production gene Ac/ac dominant or recessive?
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is the glycosides production gene dominant Li/li dominant or recessive?
also dominant
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which genotype is therefore cyanogenic?
Ac-Li, Ac-lili and acacLi- genotypes acyanogenic
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What is reason for cline in frequency of cyanogenesis in clover?
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what is the main purpose of cyanogenesis in plant?
It is a deterrent against some herbivores
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what is balancing selection?


Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies above that of gene mutation- maintains variation in pop.

Card 3


what are clines?


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Card 4


what causes balancing selection?


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what is overdominance?


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