POPULATION GENETICS, NATURAL SELECTION, SPECIATION Flashcards
What is the common misconception about evolution?
That an individual organism can evolve
In reality, natural selection can act on individuals, each organism’s traits affecting its survival and reproductive success, however, the evolutionary impact of natural seletion is apparent only in how a population changes over time
SUMMARY: natural selection acts on individuals, but populations evolve
What is microevolution?
Microevolution is a change in allele frequency in a population over generations
What allows for a population to evolve?
Mutation and sexual recomination provide the variation needed to make evolution possible
What is a mutation?
A mutation is a change in the nucleotide sequence of an organism’s DNA and can result from the formation of new alleles
Are mutations always harmful?
Most new mutations which alter a phenotype are slightly harmful, however, some are removed quickly by natural selection. Other times these harmful alleles are recessive and therefore hidden from natural selection because its harmful effects are masked by a more favorable dominant allele, allowing it to persist for generations by propogation in heterozygous individuals. However, on rare occasion, certain mutations can make its bearer better suited to an environment, enhancing reproductive success
How does sexual reproduction produce new alleles and new genes?
Sexual reproduction allows for the change in arrangement of existing gees and then deals them at random to produce individual genotypes
What 3 mechanisms contribute to shuffling in sexual reproduction?
- Crossing over
- Independent assortment of chromosomes
- Fertilization
What is the Hardy-Weinberg Equilibrium?
The Hardy-Weinberg Equilibrium states that evolution isn’t occuring and allele and genotype frequencies aren’t changing from generation to generation
What are the conditions of Hardy-Weinberg Equilibrium?
- Extremely large population size
- No gene flow
- No mutations (no new alleles)
- No natural selection
- Random mating
What is the Hardy-Weinberg equation?
How do you calculate frequency using the Hardy-Weinberg equation?
frequency = q
How to calculate genotype frequency in a population?
B^2 + 2Bb + b^2 = 1
How to calculate allele frequency in a population?
B + b = 1
What 3 main factors cause an allele frequency to change?
- Natural selection
- Results in alleles being passed to the next generation in proportions that differ from those in present generations
- Genetic drift - chance events which alter allele frequency
- Gene flow - the transfer of alleles between populations
- Can affect how well populations are adapted to local environment conditions
- Can transfer alleles that improve the ability of populatios to adapt to local conditions
What are the effects of genetic drift?
- Significant in small populations
- Cause allele frequency to change randomly
- Loss of genetic variation within a population
- Can allow harmful alleles to become fixed
What are the 2 types of genetic drift?
- Founder Effect
- Bottleneck Effect
What is the Founder Effect?
The Founder Effect occurs when a few individuals become isolated from a larger population and establish a new population whose gene pool differs from the source population
What is the Bottleneck Effect?
The Bottleneck Effect is caused by a severe drop in population size, causing certain alleles to be either overrepresented, underrepresented, or absent all together
What are the effects of gene flow?
- Causes population to either gain or lose alleles
- Decreases difference between populations over time
- Can lower the relative fitness of a population
- Decreases variation among populations with time
- Alleles moved among populations
What is the only mechanism that consistently causes adaptive evolution?
What is relative fitness?
Relative fitness is the contribution an individual males to the gene pool of the next generation relative to the contributions of other individuals
What are the 3 modes of selection?
- Directional selection - one extreme favored
- Disruptive selection - both extremes favored
- Stabilizing selection - intermediate favored
What is sexual selection?
Sexual selection is a process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates
What is sexual dimorphism?
Sexual dimorphism is a product of sexual selection in which there is a difference in secondary sexual characteristics between males and females of the same species
What is intrasexual selection?
Intrasexual selection is selection within the same sex where individuals compete directly for mates of the opposite sex (usually occurs between males)
What is intersexual selection?
Intersexual selection is selection within the same sex where individuals are choosy in selecting their mates from the other sex (usually occurs between females)
What is balancing selection?
Balancing selection is selection which may preserve variation at certain loci, this maintaining 2+ phenotypic forms in a population
What is frequency-dependent selection?
Frequency-dependent selection is when the fitness of a phenotype depends on how common it is in a population
What is an example of frequency-dependent selection?
Scale-eating fish and whether they’re “right-mouthed” or “left-mouthed”
What is heterozygote advantage?
Heterozygote advantage is exhibited by heterozygous individuals at a particular locus and have greater fitness than do both kinds of homozygotes
What is an example of heterozygote advantage?
Heterozygotes for sickle-cell are protected against malaria. This is because malaria infects RBC and the RBC of those with sickle-cell are disoriented in shape, so the body ends up destroying sickled RBC therefore killing parasites from malaria that they harbor
What is evolution?
Evolution is descent with modification
How did Aristotle contribute to Evolution Theory?
Aristotle viewed species as unchanging and believed that life could be arranged on a ladder/scale of increasing complexity called the scala naturae (linear hierarchy)
How did Carolus Linnaeus contribute to Evolution Theory?
Linnaeus developed the binomial classification system, however, it was not based on evolutionary relationship
How did George Cuvier contribute to Evolution Theory?
Cuvier noted that the older the stratum, the more dissimilar its fossils were to current life-forms, and that some new species appeared while others dissapeared from one layer to the next
Regardless of these findings, he inferred extinction was a common occurance, but opposed the idea of evolution - each strata represented a sudden catastrophic event, and the land was repopulated by different species immigrating over from other areas
How did James Hutton contribute to Evolution Theory?
Hutton proposed that Earth’s geologic features could be explained by gradual mechanisms
How did Charles Lyell contribute to Evolution Theory?
Lyell incorporated Hutton’s idea into his proposal that the same geologic processes are operating today as in the past, and at the same rate
What was Lamarck’s hypothesis on evolution?
- Use and disuse hypothesis
- The idea that parts of the body used extensively became larger and stronger while those not use deteriorated
- Inheritance of acquired characteristics
- Thought evolution happened because organism’s had a drive to become more complex
Adaptation vs. natural selection vs. artificial selection
Adaptation is the inheritance of characteristics which enhance an organism’s ability to survive and reproduce in specific environments
Natural Selection is the process in which individuals that have certain inherited traits tend to survice and reproduce at higher rates than do other individuals because of those traits
Artificial selection (aka selective breeding) is the modification of other species by selecting and breeding individuals that posess desired traits
What 4 lines of evidence prove that evolution occured via natural selection?
- Direct observations
- Fossil records
- Biogeography
- Homologies
Homologous features vs. analagous features?
Homologous features share anatomical resemblance that represents variations on structural themes present in common ancestry (e.g. arm of a human, wing of a bat, flipper of a dolophin, leg of a dog)
Analogous features share similar functions but not common ancestry (e.g. wings in flying animals, like bats, birds, and insects)
What are key features of natural selection?
- Natural selection increases the frequency of adaptations that are favorable in a given environment
- If an environment changes, or if individual move to a new environment, natural selection may result in adaptations to these new conditions, sometimes giving rise to new species
- Individuals do not evolve, but natural selection occurs through interactions between individual organisms and their environment
What can’t natural selection fashion the perfect organism?
- Selection can only act on existing variations
- Evolution is limited by historical constraints
- Adaptations are often compromises
- Change, natural selection, and the environment all interact
What is speciation?
Speciation is the processs by which 1 species splits into 2+ species
What forms a bridge between micro and macroevolution?
Speciation forms a bridge between miroevolution (changes in allele frequencies in a population) and macroevolution (the broad patters of evolution above the species level)
What are the prezygotic barriers which produce reproductive isolation?
- Habitat isolation
- Species that occupy different habitats within the same area may rarely encounter each other, if at all, even though they are not isolated by a physical barrier
- Temporal isolation
- Species that breed during different times cannot mix gametes
- Behavioral isolation
- Courtship rituals are unique to species
- Mechanical isolation
- Mating is attempted, but morphological differences prevent its successful completion
- Gametic isolation
- Sperm of 1 species may be unable to fertilize the egg of another
What are the postzygotic barriers which produce reproductive isolation?
- Reduce hybrid viability
- Genes of different parent species interact in ways that impair the hybrids development/survival abilities
- Reduce hybrid fertility
- Hybrids are sterile beccause chromosomes of parents differ in number/structure, so meiosis fails to produce normal gametes
- Hybrid breakdown
- Some first-generation hybrids are viable and fertile, however, when they mate with one another or with either parent species, the offspring of the next generation are feeble and sterile
What is allopatric speciation?
Allopatric speciation occurs as gene flow is interrupted when a population is divided into geographically isolated subpopulations
What is sympatric speciation?
Sympatric speciation occurs in populations that live in the same geographic area, however, gene flow is reduced
What are examples of sympatric speciation?
- Polyploidy
- Autopolyploidy
- Allopolyploidy
- Sexual selection
- Habitat differentiation
What is polyploidy?
Polyploidy is cell division which results in an extra set of chromosomes
What is autopolyploidy?
Autopolyploidy occurs when an individual have more than 2 chromosome sets that are derived from a single parent due to a failure in cell division
What is allopolyploidy?
Allopolyploidy occurs when 2different species interbreed, producing mostly fertile offfspring since sets of chromosomes from 1 species cannot pair during meiosis with the set from the other species
What is habitat diffentiation?
Habitat differentiation occurs when subpopulations exploit a habitat or resource not used by the parent populations
What speciation models are used to see patterns in fossil records?
- Punctuated equilibrium
- Gradual equilibrium
