Chapter 2: Evolution and Ecology Flashcards
What is the “great unifying principle of biology”?
Evolution by Natural Selection
Provide an operationally useful definition of evolution.
Evolution is a change in gene frequency
Complete this sentence: Evolution always involves…
a change in gene frequencies.
State the Hardy-Weinberg Equilibrium
“In the absence of forces that change gene frequencies in a large, randomly mating population, gene frequencies should remain the same from generation to generation.”
Define random mating
Individuals show no preference with respect to mate selection based on the trait
What is the role of mutation in the process of evolution?
It provides raw material for evolutionary change; it’s the ultimate source of all genetic novelty.
What is the role of genetic recombination in the process of evolution?
It’s the most important source of heritable variation upon which natural selection acts.
Provide two points during meiosis in which genetic variation can be introduced into the genome.
1) Crossing over during Prophase I
2) Random segregation of homologous chromosomes during Anaphase I
How can sex result in the reduction in an individual’s contribution of genes to the next generation?
Only about 50% of the producer’s genes are passed on
What is recombinational load?
The production of many individuals with unfit combinations of genes
Give two possible advantages to individual fitness that sex might provide.
1) the repair of damaged DNA through recombination
2) the masking of deleterious mutations through outcrossing
In a closed population, what two forces can lead to a change in gene frequencies?
Natural Selection & Genetic Drift
Define natural selection
Differential Reproduction: the fact that certain genotypes leave more offspring to the next generation than others
What is stabilizing selection?
If the environment is stable over time, then extreme phenotypes may be selected against, ie; birth weights in humans
What effect does stabilizing selection have on phenotypic variation in a population?
It reduces phenotypic variation.
What is Directional Selection?
If the environment is changing in a directional fashion, then selection may act against one extreme phenotype in favor of the other. ie; Britain’s Peppered Moths
What is disruptive selection?
If the environment is heterogenous enough, selection may favor forms at both ends of the phenotypic range and intermediate forms are selected against
What is the possible outcome of disruptive selection?
Could result in genetic polymorphism
Define genetic drift
Random changes in gene frequency that occur in small populations due to sampling error that leads to a reduction in genetic variability within a population as alleles are lost or fixed
Under what circumstances is genetic drift most likely?
small populations
What is the “founder effect”?
A form of genetic drift where a few individuals emigrate and begin a new popluation
What is the difference between a transient polymorphism and a balanced polymorphism?
Transient polymorphism is when frequencies of two or more alleles or phenotypes change over time. Balanced polymorphism is where frequencies of two or more alleles or phenotypes remain relatively stable over time.
Provide three ways in which a balanced polymorphism might be maintained.
1) Neutral Alleles
2) Heterozygous Advantage
3) Environmental Heterogeneity
Give an example of a balanced polymorphism thought to be maintained by heterozygote advantage
The sickle cell anemia trait in Africa where heterozygotes are favored due to their increased resistance to malaria.
What type of adaptation is seen in the evolution of melanism in peppered moths in UK?
Environmental Heterogeneity
Define the term “fitness”.
Measure of the number of offspring left by an individual (genotype) relative to the ideal (reference) genotype in the population
What range of values can W assume?
0-1
How is fitness calculated?
Survival rate divided by the largest survival rate
Give three reasons why an organism may not be perfectly adapted.
1) Availability of adaptive genes
2) Opposing selective pressures
3) Environmental Change
What is the “Red Queen Hypothesis”?
Organisms have to keep making evolutionary changes just to survive such deteriorating conditions
Under most circumstances, what is the target of selection?
The Individual
What are altruistic traits and how might they be selected for?
Traits that are promoted by group selection; they might be selected for by Kin Selection
What does the term “inclusive fitness” mean?
the total number of equivalent offspring an organism can add to the population by supporting others and the number it can add by classical fitness
What does the “sexy son hypothesis” predict and why?
That the females will pick a mate that has the best chance of passing on the most offspring to the next generation. Who wouldn’t want that?
According to the “Optimal Foraging Theory”, how should consumers forage for food?
In a way that maximizes their caloric intake per unit time or effort
How should natural selection affect two species that are potential competitors?
It reduces the fitness of all competitors involved
What is the difference between sympatric and allopatric populations?
Sympatric populations are two populations that are found together, allopatric populations are not
What is the first step in the process of allopatric speciation?
populations get fragmented by a barrier (physical ie; mountains) into two or more subpopulations
Provide two ways in which populations separated by a barrier might diverge genetically.
different selective pressures or genetic drift
Define adaptive radiation and give a possible example of adaptive radiation in nature.
The generation of a number of different forms from a basic stock ie: Galapagos finches
Complete this sentence: According to Ernst Mayr, biological species are…
“groups of interbreeding organisms that are reproductively isolated from other such groups.”
Provide a definition for reproductive isolating mechanisms.
Intrinsic properties of an organism that prevent them from interbreeding with other organisms
Are rivers, canyons, mountain ranges, etc. considered reproductive isolating mechanisms?
No, they must be within the organism itself
How can premating isolating mechanisms be improved by natural selection?
selection against less fit hybrids
What is behavioral isolation?
such things like having different mating calls and courtship patterns
What is temporal isolation?
breeding at different times
What is ecological isolation
breeding in different habitats
Give an example of a postmating isolating mechanism.
Hybrid sterility
Can postmating isolating mechanisms be improved by natural selection?
No because you cannot make a selection at that point.
what is the probable function and meaning of biological species?
Only so much variability can be accommodated in one gene pool (species), through reproductive isolation, species serve to preserve coadapted gene complexes. They allow species to become adapted to their own ecological niches.
