Evolution Flashcards
What is the relationship of ecology with evolution?
Because evolution can occur very rapidly, ecologists must be aware of evolution at all times.
Bolgard
A transgenic cotton variety that produces Bt toxin, a biological insecticide that is poisonous to larvae of butterflies and moths.
What is evolution?
(1) change in the composition of a population from one generation to the next.
(2) change in allele frequencies across generations or between populations
When does evolution happen?
Evolution happens when individuals with certain traits survive and reproduce at higher rates than others.
What would a graph of offspring vs parents look like if offspring tend to resemble their parents?
Linear
What would a graph of offspring vs parents look like if offspring tend NOT to resemble their parents?
Scattered plot
What is the theory of natural selection?
The theory of evolution by natural selection is that when there is variation (1) in a population that is heritable (2) and that influences survival and reproductive success (3), the composition of the population automatically changes from one generation to the next (evolution happens!).
Traits associated with survival and reproduction become common; traits associated with untimely death and reproductive failure become rare.
What are the assertions of the theory of natural selection?
(1) Individuals vary
(2) Heritable traits (children resemble parents)
(3) Selective survival/reproduction (non-random)
What happens when one or more of the assertions of natural selection does not apply?
The composition of the population may fluctuate across generations, but substantial change will accrue only slowly, if at all
What is the relationship between natural selection and population genetics?
The theory of evolution by natural selection can be rephrased in the language of modern population genetics.
How can you rephrase the theory of natural selection in terms of modern genetics?
(1) Individuals vary in phenotype. That is, they look, function, and act differently.
(2) Differences in phenotype are at least partly due to differences in genotype. That is, some of the variation among individuals in appearance, function, and behavior arises because they carry different alleles for some of their genes.
(3) Some phenotypes, and thus some genotypes, survive and reproduce at higher rates than others.
As a result, the relative abundances of genotypes change from one generation to the next (evolution!).
Phenotype
An individual’s phenotype is any observable or measurable aspect of its appearance, structure, behavior, or physiological function.
Genotype
An individual’s genotype is the combination of alleles the individual carries. Less formally, its genotype is its genetic make-up.
Alleles
Alleles are different versions of a gene. The term may be used to distinguish versions of a gene that differ in nucleotide sequence, amino acid sequence, or both.
Fitness
An individual’s lifetime comparative reproductive success. In practice, this is often measured as the number of offspring that are produced that themselves grow up to produce offspring.
Codominant
Codominant describes the relationship between two alleles when heterozygotes (Aa individuals, for example) have a different phenotype than either of the homozygotes (AA and aa individuals).
Typically used when the phenotype of the heterozygotes is intermediate between the phenotypes of the homozygotes.
When will phenotype not necessarily reveal genotype?
When the alleles are not codominant. (e.g. Aa looks like AA)
Frequency
Relative abundance (#with a trait/ #total individuals)
Calculate the frequency of the ll genotype if there are 4 ll individuals in a population of 10.
0.4
How can you calculate genotype counts?
individuals with genotype/#total individuals
How can you calculate frequencies of alleles A and B in a population?
Frequency of allele A = (2(AA) + AB)/(population*2)
Frequency of allele B = (2(BB) +AB)/(population*2)
Blending theory
Antiquated theory of inheritance where offspring would have some intermediate level of a trait found in both parents (e.g tall + short parents = medium height offspring)
Factors
Mendel’s initial term for what we now know as genes. He realized that inherited traits were discrete and passed on discrete factors.
What are the ways that selection could happen?
(1) Stabilizing selection
(2) Directional selection
(3) Disruptive selection
Stabilizing selection
Extreme phenotypes are less successful; average phenotype becomes more common.
Directional selection
An exceptional phenotype has greater survival and reproduction, causing the population’s mean to shift to one extreme or another.
Disruptive selection
The average phenotype is less successful than the extreme, and over time the average becomes less common and the population diverges.
What was Lamarck’s view on inheritance?
Individuals changed to meet the needs of their environment, and acquired characteristics were passed onto offspring.
What was Darwin’s view on inheritance?
Through the four postulates of natural selection, variation happens. Selection can only work on variation already present in a population. Acquired traits are not passed on.
What was the difference between Lamarck and Darwin’s view on inheritance?
Lamarck - acquired traits are inherited
Darwin - acquired traits are NOT inherited
Vicariance
Some sort of break in gene flow due to some sort of battier (stops gene flow entirely, e.g new mountain ranges or islands)
Dispersal
Process where species are separated but can still maintain gene flow between populations
What causes populations to diverge?
Some event that reduces or stops gene flow. (Though natural/sexual selection and genetic drift effects may also contribute).
Allopatric speciation
Populations split by vicariance are then subject to selection
Sympactric speciation
Sub-population arises within the parent population and diverges, giving rise to a genetically distinct species
What is an example of sympatric speciation/ when might it occur?
May occur through reproductive isolation or new resources (one subpopulation uses the new resource, while main population primarily uses old resource).
An example is the introduction of green apples in north america, providing a new resource for apple maggots which have split genetically to match the food source.
Central dogma
DNA –> RNA –> Protein –>
Replication –>Transcription –> Translation
What are Mendel’s laws?
Law of:
(1) Segregation–only one of an individual’s two alleles for each gene is passed onto offspring.
(2) Independent Assortment–alleles transmitted independently of each other.
Law of segregation
Each individual has two alleles for each gene. A parent passes on only one of these two alleles to their offspring.
XY ——-> X or Y is passed on.
Law of independent assortment
Alleles are transmitted independently of one another.
Dihybrid cross
SsYy x SsYy –> phenotypes: 9 SY: 3 Sy : 3 sY : 1 sy
Hardy Weinberg Equilibrium Model
Mathematical model to predict allele frequencies in the absence of evolutionary forces.
What are the assumptions of the Hardy Weinberg equilibrium model?
(1) Random mating
(2) No mutation
(3) Large population size
(4) No migration
(5) No natural selection
Migration
The regular cyclical movement of a species through its environment (moves back and forth)
Dispersal
The permanent movement of individuals from parental habitat to somewhere else (unidirectional)
Open Population
Populations without barriers to dispersal. Individuals travel broadly over large geographic distances.
Connectivity
The demographic and genetic exchange of material facilitated by dispersal.
Closed populations
Populations characterized by “self-recruitment” with little or no exchange with outside populations. No connectivity
Mutation
Random changes in the DNA of an organism that can have varying degrees of effects on the function and/or product of a gene.
Genetic Drift
The random change in the frequency of alleles in a population, not influenced by the environment or behavior, but by chance (e.g. Founder’s effect, bottleneck)
What is the difference between Founder’s effect and bottleneck effect?
Founder’s effect is moving to a new habitat, whereas bottleneck effect occurs in the same habitat.
What factors influence phenotype?
(1) Genotype - genetic makeup of individuals
(2) Environment - local conditions can sway plasticity
(3) Noise - unexplained developmental quirks
What drives/influences heritability?
Genetic variation (Vg) and phenotypic variance (Vp)
What are the factors contributing to phenotypic variance?
Genetic (Vg) and environmental (Ve) effects.
What is an equation describing the forces that drives heritability?
h^2 = Vg / (Vg + Ve)
How does increased genetic variation affect heritability?
Increases
How does increased environmental variation affect heritability?
Decreases
What are the types of heritable traits?
(1) Discrete
(2) Quantitative
Discrete trait
A trait where you receive one of two/several distinct forms (e.g. blood type)
Quantitative
A trait that has a continuous distribution (e.g. height)
What kind of heritable trait contributes to phenotypic plasticity?
Quantitative traits
Compare adaptation with evolution
Adaptation = species maintains plasticity to survive in a range of habitats (temporary)
Evolution = tied to speciation, formation of discrete, separate unit (more permanent)
