Flashcards
population genetics and evolution
Cards in this deck (55)
- 1The process of temporal changechange over time
- organisms (heritable traits, characteristics) come to differ from ancestors (permanently) - 2Heritablecharacteristics passed on - traits are genetic and are often (not always) expressed in phenotype
- 3The two processes of evolutionary changeTransformation
splitting/branching - 4TransformationAnagenesis: between-generation change within a single lineage. Usually the ancestral form disappears as the entire species changes to a new form
- 5splitting/branchingCladogenesis - Division of a single lineage due to genetic divergence. Subsequent changes (anagenesis) occurring in both/either of the sister lineages results in further divergence (cladogenesis)
- 6PhylogeniesBranched evolutionary histories -
study/reconstruction of phylogenies is known as phylogenetics - 7Microevolutionwithin-species evolution (Intraspecific evolution) - evolution at the population level
-microevolution includes process leading to speciation (mainly via cladogenesis) - 8MacroevolutionEvolution at the species level & above
e.g. genus, family
- interspecific evolution
involves: 1. speciation events 2. subsequent divergence of species & higher taxa - 9characters/traitsany measurable item on an organism e.g. height
- 10character stateAlternative variants of a character (e.g. eye colour in human)
- 11GENOTYPEinfo stored in the DNA of one individual e.g genes
nucleus (linear chromosomes)
mitochondria (circular chromosomes)
mitochondria derived from endosymbiotic bacteria - 12Junk DNAsequences within introns of genes and those between genes
80% of junk dna does have a function
'true junk dna' - is assumed not to be subject of natural selection - 13Nucleotide base sequences(genetic variation within individual organisms) that make up the same gene may differ between individuals.
- 14alleles of the same gene and polymorphic locusWhen nucleotide sequences differ at the same site ( locus) on the paired homologous chromosomes they are termed different alleles of the same genes and polymorphic locus
- 15Definition of genotypeEvolutionary biologists - Info stored in all of the genes of one individual
Population geneticists - the combination of alleles at one or more studied / examined loci in one individual - 16Phenotypethe observable/measurable/detectable characteristics of an organism - easiest to observe/record/quantify and variation in most phenotypic traits is at least partly genetically determined
- 17extended phenotypee.g. nests
- 18Variation in a phenotypic traitnot all are heritable - some variation may be due to non-genetic factors such as wear/trauma. disease, somatic mutation
- 19Evolutionary importance of heritable trait variationheritable intra-population variation is essential for evolutionary change to occur - there must be a sufficient amount of such variation
- 20Example 1 : pathogens of cropLate potato Blight & the great irish famine - caused by phytopthora infestans
'water mould'
potatoes were of just one variety and were propagated asexually - if the potato had been more genetically diverse the famine might have been averted - 21Why is there a lack of sufficient heritable trait variationdue to cloning by farmers (asexual reproduction, which produces progeny that are genetically identical to the parent)
- 22Example 2: pathogen of cropBlack sigatoka disease in bananas -
problems made worse by
1. cultivation of only a few banana varieties, most of which are vulnerable
2. these varieties are propagated asexually
3. genetic variability of fungus (has allowed it to evolve resistance to fungicidal chemicals applied by farmers) - 23Classification of phenotypic variationcontinuous traits (intermediates exist between 2 extremes)
discontinuous/discrete traits (no intermediates exist) - 24discontinuous phenotypic trait variation-one or a few gene loci involved
-usually only a few alleles involved at such loci
- allele-for-trait effect clearly evident in the phenotype - 25continuous phenotypic trait variation-many gene loci involved
- many alleles involved
- it is harder to discern the contribution of the individual alleles to the phenotype - 26variation in higher organisms (eukaryotes)inheritance variation
environment variation - 27inheritance variationcontinuous - polygenic (many loci with small effect)
discontinuous - few loci (sometimes only 1) with major effect - 28Environment variationcontinuous - often plays a role
discontinuous - little effect - 29How to quantify population variation?Sampling -
representative (unbiased) samples needed
- take a random large sample - 30measurement of variationmeasurement among individuals - (continuous)
scoring among individuals - discontinuous - 31mean and variancecan compare with other samples e.g. by t-test
- 32The phenotype is used by evolutionary biologists as a ‘proxy’ or ‘surrogate’i.e. a shorthand for the genotype
- 33microevolutionhow populations ('gene pools') change - over time,
in the relative abundance of genotypes or phenotypes - 34what is population geneticsProcess that create genetic variation
- mutations
-recombination (shuffles genetic variation)
process that remove genetic variation
-Everything else
-genetic drift - random changes in allele frequencies
-selection - not random changes in allele frequencies (natural/artificial) - 35genetic driftrandom changes in allele frequency
reproduction is random
effect over time - loss of heterozygosity - 36Genetic drift and inbreeding and linkage disequilibriumInbreeding - mating between relatives
linkage disequilibrium: non-random association between loci (3 possibilities)
linkage equilibrium: random association between loci ( a correlation! ) - 37Adaptive evolutionary changewhen subjected to natural selection or its mimic, artificial selection: genetically - determined (=heritable) phenotypic traits correlated with fitness typically alter in frequency (% or proportion) within a population
This is directed (i.e. non random) change - in response to a change in environmental variables
e.g. evolution of insecticide resistance
overall it is where under natural conditions, the genetic variant conferring higher fitness increases in relative abundance within the gene pool e.g. proportion of variant A increases, while proportion of variant B decreases reciprocally - 38Artificial selectionmimics natural selection
breeder - decides trait
leads to adaptive evolution under artificial conditions but does not necessarily correspond to differential fitness under natural conditions - 39Are all of an organisms heritable phenotypic traits either adaptive of maladaptiveno.
there are selectively neutral genes whos frequencies are not Influenced by natural selection - 40neutral evolutionary changefrequencies of variants of neutral traits can change over time within a population
but its undirected (random) evolutionary change
neutral genes are known to be linked to adaptive function genes - in which case they will be subject to selection as they are close together - 41Examples of selectively neutral phenotypic traitsmarking on clover leaves, markings on cone shells - no adaptive significance, may be selectively neutral or they could be adaptive (pleiotrophy)
- 42Pleiotropy-Multiple phenotypic effects of an individual gene
- Effect on one phenotypic trait can be adaptive
- while effect on other trait may be neutral, deleterious or positive
reproduction vs ageing
- male: testosterone increase fitness early, prostate disorders later one
-females - pregnancy and lactation decrease bone mineral density - osteoporosis later on - 43Three kinds of selectionnegative - pushes into middle
positive - pushes to the right
balancing - pushes down - 44fitness1. adaptive traits are correlated with fitness
2. neutral phenotypic traits are not - 45selection1. adaptive traits are subject to selection within the population
2. neutral traits are usually not - 46random changeadaptive and especially neutral traits can be subject to random changes in frequency within a population i.e. evolutionary changes in the traits do not necessarily occur as the result of natural selection (non-random process) - can occur from genetic drift (random process)
- 47what if the selection pressures acting on an adaptive trait are completely eliminated from the environment?via extinction of a major predator - the trait will become selectively neutral until new predator arrives
- 48phenotypic plasticityphenotypic expression of genotype is often environmentally determined
-only some phenotypic expressions of the genotype are 'beneficial' (are optimal)
- most others are suboptimal - 49adaptive phenotypic plasticityEach one of the different phenotypic expressions of genotype is beneficial (optimal).
• e.g. skin darkening & lightening in response to sun exposure in humans.
• Pale skin: admits UV light for vitamin D production –advantageous in winter.
• Dark skin: protects against too much UV –advantageous in summer.
another example - water buttercup
leaf morphology varies according to whether the leaves are above/below water surface
full leaves : optimal for above - water
branched leaves: optimal for below - 50constraints upon evolutionary change- evolutionary change does not always happen
- 51Types of constraint upon evolutionary change-Insufficient genetic variation exists in the gene pool
- no selection pressure operating
- sufficient selection pressures, BUT there exists constraints upon changing the 'design' - 52Design constraintsthe genome of organisms is a coevolved integrated assemblage of genes
it cannot be simply unravelled to produce a radically new structure to solve an environmental problem/challenge - 53Example of a design constraintarachnid, myriapod & insect body size
- primarily terrestrial animals: need to shed their exoskeleton
-if they were very large, their bodies would collapse under their own weight at the moult
- the respiratory mechanism would also not work efficiently therefore why they are small in size
- this limit on body size is a phylogenetic constraint (found within entire group of descendants from a common ancestor) it cannot be undone - 54Is evolution goal-directed?- NO
-Lineages do not comprise a series of prototypes culminating in a final perfected model
-generations within a lineage are adapted to the prevailing conditions
(there may be brief phases of un-adaptedness - 1. in a population colonising a new habitat 2. if the habitat changes rapidly - 55Red queen hypothesispredator and prey constantly evolve together - cycle
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- Degree Genetics Flashcards on population genetics and evolution, created by Sara Forghani on 18/05/2017.
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