Exam 2 (Ch 7-11) Flashcards
A sub discipline that investigates how allele frequencies and genotype change over time.
Population genetics
Given a set of allele frequencies, the expected set of genotype frequencies that will be observed under the HW model.
Hardy-Weinberg equilibrium
A measure of strength of natural selection for or against a specific phenotype or genotype.
Selection coefficient
When an allele replaces all alternative alleles at the same time; happens when one allele is constantly favored over another; results from underdominance
Fixation
A form of selection in which the fitness associated with a trait is not directly dependent upon the frequency of that trait in a population.
Frequency-independent selection
A stable equilibrium in which more than one allele is present at a locus.; results from over dominance
Balanced polymorphism
Overdominance is associated with…
Heterozygote advantage
A form of frequency-independent selection in which heterozygote genotype have higher fitness than the corresponding homozygote genotypes
Overdominance
A form of frequency-independent selection in which the heterozygote genotype has a lower fitness than either corresponding homozygote genotype.
Underdominance
A measure of the ability to produce offspring
Fecundity
An equilibrium frequency of deleterious mutations in which these deleterious mutations are maintained at a positive frequency in a population because of a balance between ongoing deleterious mutation and the purging effect of natural selection
Mutation-selection balance
A mating pattern in which individuals with dissimilar phenotypes or genotypes mate with one another.
Disassortative mating
When two or more gene copies are identical because of shared descent through a recent common ancestor.
Identical by descent
A decrease in fitness that results from individuals mating with genetic relatives
Inbreeding depression
A statistical measure of the degree of homozygosity in a population; an inbreeding coefficient
Wright’s F-statistic
A population genetic model of evolutionary change in small populations with non-overlapping generations. aka the HW of small populations
Wright-Fisher model
Random fluctuation in allele frequencies over time due to sampling effects in finite populations.
Genetic drift
Alternative alleles are selectively neutral when there is no fitness difference between them.
Selectively neutral
The fraction of individuals in the population that are heterozygous at a given locus
Observed heterozygosity (Ho)
The size of an idealized population (no migration, mutation, assortative mating, or natural selection) that loses genetic variation because of genetic drift at the same rate as the population under study
Effective population size
A theory developed to study the gene–genealogical relationships in a population by tracing the ancestry of gene copies backward from the present through a finite population.
Coalescent theory
The point on a gene tree that delineates the gene copy that is the most recent common ancestor of the genes being studied in a population.
Coalescent point
A brief period of small population size. Population bottlenecks reduce genetic diversity and can accelerate changes in allele frequencies due to genetic drift.
Population bottleneck
A change in allele frequencies that results from sampling effects that occur when a small number of individuals derived from a large population initially colonize a new area and found a new population. Ex: Manx cat
Founder effect
The process by which a species expands into a previously unoccupied area. The individuals colonizing the new area will tend to come from the populations nearest this region, and as a result populations in the newly colonized area will tend to exhibit a reduced genetic relation to those in the source population.
Leading edge expansion
The hypothesis that at the molecular level of DNA sequence or amino acid sequence, most of the variation present within a population and most substitutional differences between populations are selectively neutral.
Neutral theory
The process in which a new allele arises by mutation and is subsequently fixed in a population.
Substitutions
A nonfunctional and typically untranslated segment of DNA that arises from a previously functional gene.
Pseudogene
Selection against deleterious mutations.
Purifying selection
A technique for assigning relative or absolute age based on genetic data. In their simplest form, molecular clock methods assume that substitutions at neutral loci occur in clocklike fashion, and so researchers use genetic distances between populations to estimate the time since divergence.
Molecular clock
The principle that if molecular evolution proceeds at the same constant rate over time in different lineages, all members of a clade should be genetically equidistant from an outgroup to the clade.
Genetic equidistance principle
The hypothesis that most polymorphisms and most substitutions, if not strictly neutral, are only mildly deleterious—and that because of relatively small population sizes, natural selection is unable to purge these deleterious variants.
Nearly neutral theory
Traits that are affected by many genes simultaneously.
Polygenic traits
Genetic contributions to phenotype for a polygenic trait, in which the effects of each allele sum together to determine phenotype.
Additive genetic effects
The phenomenon in which alleles at two or more loci interact in nonadditive ways to determine phenotype
Epistasis
The range of potential phenotypic variants that could be produced given the current genetic variation in the population, but are not observed because the necessary combinations of alleles are not realized in the population.
Latent variation
A haploid set of alleles, i.e., one at each locus
Haplotype
The presence of statistical associations between alleles at different loci.
Linkage disequilibrium
A measure of nonrandom association between alleles at two different loci. The difference between the actual frequency of a haplotype and the expected frequency of that haplotype if there were no association between alleles at one locus and alleles at the other locus.
Coefficient of linkage disequilibrium
Linkage disequilibrium in which the coefficient of linkage disequilibrium D is positive.
Coupling
Linkage disequilibrium in which the coefficient of linkage disequilibrium D is negative.
Repulsion
A process in which a series of clones carrying beneficial mutations successively go to fixation in an asexual population.
Periodic selection
A phenomenon in which a selected allele goes to fixation, carrying with it alleles at physically linked loci.
Selective sweep
The process by which a neutral or even disadvantageous allele is able to “ride along” with a nearby favorable allele to which it is physically linked, and thus increase in frequency.
Genetic hitchhiking
A process by which neutral or beneficial alleles are lost because they are physically linked to nearby deleterious alleles. Deceases genetic variation relative to what would be expected in a neutral model.
Background selection
A source of randomness in the evolutionary process due to the happenstance of the genetic background on which a new mutation arises. Some mutations will rise to high frequency because they arise on a favorable background; others will be lost because they arise on an unfavorable background.
Genetic draft
An overall reduction in the rate at which beneficial alleles are fixed in asexual populations due to competition among alternative beneficial mutations.
Clonal interference
A heuristic representation of fitness as a function of genotype or phenotype. Commonly used by biologists to envision the course of evolutionary change.
Adaptive landscape
Combinations of traits associated with the greatest fitness values on an adaptive landscape.
Fitness peaks
Combinations of traits associated with lower fitness values on an adaptive landscape.
Fitness valleys
A conceptual model in which similar phenotypes occupy nearby points on a plane. Adaptive landscapes are often illustrated in this type of model.
Phenotype space
A conceptual model in which similar genotypes occupy nearby points on a plane
Genotype space
A mathematical approach to the population genetic study of continuously varying traits.
Quantitative genetics
The fraction of the phenotypic variance that can be attributed to genetic causes of any type and thus is potentially heritable.
Broad-sense heritability (H2)
Interactions between two alleles at the same locus in determining phenotype.
Dominance effects
The fraction of the total phenotypic variation that is due to additive genetic variation and thus is readily accessible to natural selection.
Narrow-sense heritability (h2)
In quantitative genetics, the difference between the mean trait value of the individuals who reproduce and the mean trait value of all individuals.
Selection differential (S)
In quantitative genetics, the difference between the mean trait value of the offspring population and the mean trait value of the parental population.
Selection response (R)
A technique for identifying the regions of the genome in which quantitative trait loci occur.
Quantitative trait loci mapping (QTL mapping)
Loci responsible for quantitative—that is, continuously varying—traits.
Quantitative trait loci
Narrow-sense heritability values estimated by using values of the selection differential and selection response in the breeder’s equation.
Realized heritabilities
What is a common misconception about dominant and recessive alleles that is clarified by the works of Punnett and Hardy?
The misconception is that alleles change in frequency simply because they are dominant or recessive.
What relationship does population genetics investigate?
The relationship between the genotype frequencies in an offspring population and a parental population.
What are the 5 assumptions of the HW equilibrium?
- Natural selection is NOT operation on the trait
- Random mating (not assortative)
- No mutation
- No migration into or out of the population
- Population is infinite in size (genetic drift is negligible)
Is sickle cell anemia an example of overdominance or underdominance?
Overdominance
The most extreme type of inbreeding is self-fertilization, also called…
Selfing
What example was given for disassortative mating?
The white-throated sparrow
What was the conclusion for the example given to illustrate disassortative mating?
White-striped (aggressive) females were able to dominate their tan-striped rivals and mate with the tan-striped males; therefore the tan-striped females get left with the white-striped males
Does variation within population increase or decrease as a result of natural selection?
Decreases (except in cases of balancing selection)
Does variation within population increase or decrease as a result of mutation?
Increases
Does variation within population increase or decrease as a result of nonrandom mating?
No effect on allele frequencies (in the absence of sexual selection)
Does variation within population increase or decrease as a result of migration?
Increases
Does variation between populations increase or decrease as a result of natural selection?
Increases if selective conditions differ, decreases if conditions are the same
Does variation between populations increase or decrease as a result of mutation?
Increases
Does variation between populations increase or decrease as a result of nonrandom mating?
No effect on all frequencies (in the absence of sexual selection)
Does variation between populations increase or decrease as a result of migration?
Decreases
What are the three general consequences of genetic drift?
- In a finite population, allele frequencies fluctuate over time, even in the absence of natural selection
- Some alleles are fixed other are lost, and the fraction of heterozygotes in the population decreases over time
- Separate populations diverge in their allele frequencies and in terms of which alleles are present
The rate at which allele frequencies fluctuate over time depends on…
The size of the population
Does fixation occur quicker in small or large populations?
Small
Does genetic drift cause an increase or decrease in heterozygosity?
Decrease
The fraction of heterozygotes expected under HW equilibrium.
Expected heterozygosity (He)
What example was given to illustrate leading edge expansion?
The Black Spruce species taking over land previously occupied by a glacier
What factor contributed to the difference in alleles in the illustration of leading edge expansion?
Seeds (containing nuclear and mt DNA) were distributed locally, and pollen grain (containing only nuclear DNA) were dispersed across long distances; therefore between the populations showed a 10x greater difference in mtDNA than nuclear DNA
How old are the microfossils that were discovered in South Africa in 2010?
Approximately 3.2 billion years old
How old is the Earth estimated to be?
Approximately 4.5-4.6 billion years old
What are the 6 properties if living things?
- Homeostasis
- Structural organization
- Metabolism
- Growth and reproduction
- Response to environmental conditions or stimuli
- Is subject to, and appears to have evolved by, the process of natural selection
What does the acronym LUCA stand for?
Last Universal Common Ancestor
What does a protocell consist of?
Gene products, nutrients, some sort of membrane for compartmentalization, and genetic material
The chemical formation of life from nonliving material
Abiogenesis
What chemicals were used in the prebiotic soup hypothesis in 1953 (Stanley Miller)?
Methane, hydrogen and ammonia
When two or more molecular substrates each contribute in a positive way to the replication of the other, this is called…
Molecular mutualism
Favorable selection would depend on the costs and benefits of ….
Encapsulation
What are the 4 benefits of encapsulation?
- Control of microenvironment
- Creation of chemical gradients
- Defense mechanism against predatory replicators
- Function partitioning
What are the distinctions that makes DNA more favorable as the main carrier of genetic information?
- More chemically stable than RNA
- Deoxyribose is less reactive than ribose
- Double-strandedness
- Proof-reading capabilities
- Repair mechanisms (using one strand to fix the other that has been damaged)
- Fewer mutations and longer genes
Species concept: a lineage of … populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate
The Evolutionary Species Concept
What are the 4 most practical and widely used species concepts?
- Phenetic
- Biological
- Ecological
- Phylogenetic
Species concept: draws species boundaries around cluster of phenotypically similar individuals or populations
Phonetic Species Concept
Specific way to correlate traits and find commonalities by condensing multiple variables into a single axis
Principle component axis
Who first introduced the Biological Species Concept?
Ernst Mayr
Species concept: groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups
Biological Species Concept
What are three main issues associated with the biological species concept?
- Doesn’t account for extinct organisms
- Doesn’t account for occasional hybridization
- Doesn’t account for asexual species
Species concept: a cluster of individuals that occupy the same niche
Ecological Species Concept
Species concept: draws species boundaries using shared derived characters that are unique to one monophyletic group and absent from all other populations in the phylogeny
Phylogenetic Species Concept
What are the three models of speciation?
- Allopatric
- Sympatric
- Parapatric
Model of speciation referring to geographical isolation?
Allopatric
Model of speciation referring to populations in which distributions abut one another?
Parapatric
Model of speciation referring to populations living in the same location?
Sympatric
Allopatric speciation in which 1 large population is divided into 2 still large populations?
Vicariance
Allopatric speciation in which the divided populations differing size?
Peripheral isolate
What are two factors that could drive sympatric speciation?
- Resource competition
2. Reproductive isolation
