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60 Cards in this Set
- Front
- Back
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Qualitative (Discrete) Traits
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- can be categorized
- influenced primarily by a single locus with few alleles - Mendelian - variation around the mean |
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Dominance-recessive relationship
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alleles yield two phenotypes
- recessives can be common or uncommon |
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Incomplete-dominance relationship
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phenotypes can show any pattern of relative abundance
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Quantitative (Continuous) traits
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- traits exhibit continuous
variation in trait values that cannot be clearly divided into categories - influenced by multiple loci, each of small effect - show a normal distribution |
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Causes of Variation in Categories
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- environmental variation: variation in temperature, nutrients, predators, etc. can influence phenotype
- loci of minor effect: many loci can have minor effects on traits |
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Causes of continuous distribution of phenotypes
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- multiple alleles at a single locus (adding more alleles would "blur" the categories
- Mendelian trait with 2 alleles, incomplete dominance, and a lot of environmental effect - ** none of these are true quantitative traits |
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Quantitative Trait Loci
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- loci that influence quantitative traits
- loci that have subtle effects |
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Sources of Variation in F2
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- independent assortment at QTLs that are not linked
- recombination of linked loci |
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Marker loci
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- DNA sequences of known location on chromosome
- must be many of them, and widely distributed over all of the chromosomes - can be detected with simple genetic methods - where alleles differ between phenotypically different selected lineages, populations, or species - used to find linked QTLs that influence trait of interest |
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Microsatellite Loci
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- successfully used marker loci
- regions of the DNA where 2, 3, 4 base pairs are repeated (tandem repeats) - repetition makes these regions vulnerable to mistakes during DNA replication - duplicates are easily acquired or lost |
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Flanking Region
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- unique sequence of base pairs on either side of a microsatellite loci
- used to identify the microsatellite |
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Choosing parents of different phenotypes
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- from different populations or closely related species
- must be able to interbreed - should "breed true" to trait of interest |
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Identifying (potentially) informative loci
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- the loci at which the two parents do not share the same allele, so as to determine, by the allele, which parent the DNA is from
- doesn't mean the locus will be informative (depends if it's a QTL) |
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What makes interpretation of informative loci unclear?
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- individual loci have small effect on phenotypes
- the genetic background is complex (many polygenic modifiers) - effects of environment despite efforts to control environment |
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Candidate Locus Approach
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- used to determine identity of functional gene
- may find locus because it has similar functions in other organisms (homology) - examples: ALx-4 locus in Great Pyrenees and mice. Runx-2 locus in dogs. changes in relative # of tandem repeats affects snout size in dogs |
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D4DR
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- neurotransmitter receptor
- 48 bp tandem repeat - repeats from 2-8 times - different repeats have different physiological properties - influences thoughts and emotions in humans - genotyped 315 ppl: individuals with at least 1 long allele (6-8 repeats) scored higher on novelty seeking scores. explained 3-4% of variance - ** suggests that the number of tandem repeats within a gene can influence gene expression |
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Sexually Dimorphic (stickleback)
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males assume a bright nuptial coloration while females remain drab during reproduction
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Adaptive Radiation
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diversification partly caused by natural selection, enhancing fitness of populations in new environments
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Oceanic Stickleback
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- geographically uniform today
- always fully armored - "living fossil" - exhibit stasis - huge pop. size causes random genetic change to be unlikely - live in stable environment => can move to habitats they are used to when there is a change |
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Stasis
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absence of evolutionary change
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Freshwater Stickleback populations
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- many thousands derived from oceanic colonists in last 12,000 yrs
- given rise to innumerable genetically differentiated populations - have repeatedly and independently given rise to similar ecotypes |
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Bottlebrush model
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oceanic stickleback exhibit stasis and give rise to many freshwater populations that evolve rapidly and also often suffer from rapid extinction due to the ephemeral nature of freshwater habitats
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Ecotype
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similar genetically based phenotypes that have repeatedly and independently evolved in similar habitats
- ex. benthic and limnetic stickleback |
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Parallel Ecotypic Variation
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genetically differentiated ecotypes that have evolved repeatedly and independently
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Limnetic stickleback
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- slender body
- mouth and eyes positioned for feeding on plankton - closely spaced gill rakers used to strain plankton from water - smaller than benthic - live in deep oligotrophic lakes with little littoral zone |
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Benthic stickleback
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- deeper bodied, good for maneuvering, not speed
- large mouth for feeding on benthic invertebrates - short, stubby widely spaced gill rakers - live in mesotrophic lakes with more littoral zone |
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Eutrophic zone
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depth to which there is sufficient light penetration for net positive photosynthesis
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Littoral zone
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area of lake in which eutrophic zone reaches the substratum
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Group Cannibalism
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male stickleback defend young in a nest from group cannibalism in benthic and oceanic populations only.
- they preform a diversionary display or tactic to divert threats |
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Armor phenotypes
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- spine length
- lateral plates - pelvic girdle - all evolve rapidly |
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Spine Length
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- the longer the spine the harder for a predator to swallow
- occurs in environments with more predation |
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Lateral Plates
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- disappear quickly in most freshwater populations
- causes for loss: "relaxed selection" from piscine predators with teeth that puncture sides, or lakes are low in calcium and plates are high in cost so calcium can be used elsewhere - under control of Mendelian trait |
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Pelvic Girdle
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- lost quickly in lakes few predators and low calcium
- under control of Mendelian trait - it is to re-evolve in populations that have some partially functional pelvic girdles in some individuals in the population |
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Life Histories
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- highly variable
- not as strong as ecotypic variation - female sticklebacks are good models b/c they have a particular behavior when courting so we can tell when eggs are mature. this allows us to studying them better |
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Example of Speciation due to behavior
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Stickleback nesting: in limnetic populations, male stickleback builds a tubular nest and courts the female by swimming in a zig zag formation and displaying his red belly while sticking his head in the nest.
in benthic populations, females do the courting via "dorsal pricking", this often occurs in cannibalistic populations |
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Example of Speciation due to coloration
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- courtship coloration in males, they become dark red during mating season
- in populations where water is red due to plants in water, it is better to be black |
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Character Polarity
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Direction on evolutionary change
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Species Pairs
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Double Invasion
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- oceanic fish invade small shallow freshwater lakes
- 2nd invasion: the benthic species already there outcompeted the oceanic fish so the oceanic fish adapted to a different niche (limnetic) and fed on plankton and nested elsewhere - prediction: limnetic most closely related to oceanic |
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Spympatric Speciation Hypothesis
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- (very unlikely) oceanic stickleback invade a freshwater lake and once there they separate into different niches resulting two new benthic and a limnetic species.
- prediction: benthic and limnetic fish are most closely related. |
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Benka Lake
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- good example of polymorphic populations
- there is an island in the middle with very steep drop offs - benthic sticklebacks forage and breed in shallow bays - limnetic types forage and breed at steep drop offs by shoreline - clear difference in body shape (morphology) |
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Schistocephalus solidus
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- tapeworm with many stages of production
- does not become a segmented worm until it reaches its definitive host (birds) - develops in stickleback: once ready to reach host, causes pigment loss in fish and blackens its eye. It causes the fish to go into hypobulemic shock and it becomes very lethargic and floats near the surface of the water making it very susceptible to birds |
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Broad Sense Heritability
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degree of genetic determination of a trait, includes all genetic variation
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Heritability
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- the tendency of offspring to resemble their parents because of genetic similarity
- fraction of the total variation in a trait that is due to genetic differences among individuals = Vg/(Vp+Ve) range of 0-1 |
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Genetic Variation
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- variation among individuals due to variation in their genes
- components: additive genetic variation (Va) + dominance genetic variation (Vd) Vg = Va + Vd |
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Additive Genetic Variation (Va)
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- differences among individuals in a population that are due to additive effects of genes
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Dominance genetic variation
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- differences among individuals in a population that are due
to non-additive effects of genes. - if a certain amount of selection is imposed it is hard to predict the shift in response to selection |
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Phenotypic Variation (Vp)
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total variation in a trait among individuals in a population
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Environmental Variation (Ve)
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variation among individuals due to environmental influences on phenotype
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Additive Genetic Variance
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- differences among individuals in a population that are due to additive effects of genes
- contribution an allele makes to the phenotype that is independent of identity of other alleles at the same or different loci - responds predictably to selection - used in quantitative genetic models - component of genetic variance to which evolutionists usually refer - also know as "narrow sense heritability" |
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Narrow Sense Heritability
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additive genetic variance
h^2 = Va/Vp = Va/(Va + Vd + Ve) |
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Hardy-Weinburg Equilibrium (Genetic Equilibrium)
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- the absence of change in allele and genotype frequencies between generations (NO EVOLUTION)
- no change in genotypic frequencies between generations p^2 + 2Pq + q^2 = 1 p = proportion of dominant alleles in a population q = recessive |
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Hardy-Weinburg Conditions
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- no mutation
- random mating - infinitely large population - no differential reproductive success - no gene flow |
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Random Mating
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- different fromt he rest of the HW conditions because nonrandom mating does not alter allele frequencies
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No Mutation
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- mutation is rare and does not generally alter allele frequencies
- it can change the proportion of alleles - occasionally creates novelty |
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Infinitely Large Population
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- sampling error can not occur in an infinitely large population size
- no genetic drift - of course this does not occur in real life |
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No differential reproductive success
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no natural selection occurs
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No Gene Flow
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- no immigration from another population with different allele frequencies
- no emigration to another population |
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Genetic Drift
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- can cause evolution
- random changes in allele frequency in a population across generations - can lead to random loss of alleles = loss of genetic diversity |
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Heterozygosity
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- frequency of heterozygotes in a population
- decreases most rapidly in small populations because rapidly become lost or rare - assuming random mating heterozygosity = 2pq - as one allele declines in frequency, heterozygosity declines |
