Chapter 23: Evolution of Population Flashcards
What is microevolution?
- Change in allele frequencies in a population over generations
What are three mechanisms that cause allele frequency?
- Natural Selection (only one that causes adaptive evolution)
- Genetic Drift
- Gene flow
Adaptive Evolution: favor beneficial traits and eliminate harmful ones
What are the elements of Genetic Variation?
- Caused by differences in genes
- Phenotype: inherited genotype x environmental influences
- Discrete characters (classified on either-or basis) & Quantitative characters (vary within a population) contribute to this
- Measured as gene variability - avaerage heterozygosity (measures mean % of loci in the heterozygous population)
- Also measured as nucleotide variability - comparing DNA sequences of pairs
What is geogrpahic variation in relation to genetic variation
- Differences between gene pools of separate population
- Ex: maderia home to several isolated populations of mice
- Chromosomal variation among population is due to drift
- Ex of geographic variation occuring is as a cline
- Cline: graded change in a trait along a geographic axis
- Ex: fish vary in a cold-adapative allele along a temp gradient
What are some sources of genetic variation?
- Formation of new alleles: passing of mutation in nucleotide sequence of DNA
- Point mutation: can be neutral, harmful, or benefical
- Delete & rearrange mutation: typically harmful
- Duplication: not as harmful - Rapid Reproduction: Mutation rates low in animals, plants, prokaryotes and high in viruses
- Sexual Reporduction: recombination of existing alleles into new combinations helps produce genetic differenced making adaptation possible
What is the Hardy-Weinberg Equation’s importance?
- Used to test whether a population is evolving
- Population: localized group of individuals that can** interbreed** and produce fertile offspring
- Gene pool: consists of all alleles for all loci in a population
- Locus is fixed if population are homozygous for same allele
What are two ways that frequency for an allele in a population can be calculated?
- Diploid organisms: # of alleles at locus = total # of individuals times 2
- # of dominant alleles at a locus is 2 for each homozygous individual plus 1 allele for each heterozygous
Describe the Hardy-Weinberg equation in more detail
- 2 alleles present at a locus
- p + q = 1 (p is dominant and q is recessive)
- p^2 + 2pq + q^2 = 1 (pq is heterozygous)
- Describes a population that is NOT evolving (meets criteria meaning its is not evolving)
- Principle: states that allelic frequencies and genotypes remain constant from generation to generation
What are the five conditions for nonevolving populations?
- No mutations
- Random mating
- No natural selection
- Extremly large population size
- No gene flow
How do you apply the Hardy-Weinberg Principle?
PKU: Locus that causes phenylketonuria
1. PKU gene mutation rate is low
2. Mate selection is random
3. Natural selection acts on just rare homozygous individuals
4. Population is large
5. Migration has no effect b/c other populations have similar allele frequencies
What are the elements of Genetic Drift?
- Describes how allele frequencies fluctuate unpredictable from one generation to next
- Effects: Genetic Drift…
1. Significants in small populations
2. Cause allele frequencies to change randomly
3. Lead to loss of genetic variation in populations
4. Causing harmful alleles to be fixed
What is the difference between Founder effect and Bottleneck effect?
- Founder effect: few individuals become isolate from larger population
- Bottleneck effect: sudden reduction in populaiton size due to change in environement (ex: human activity)
What is gene flow?
- Movement of alleles among populations
- Alleles transferred via movement of fetile individuals/gametes (ex: pollen)
- Reduced variation over time
- Increase fitness of population (ex: spread of alleles for resistance of insecticides increases fitness for mosquito population)
- Important in evolutionary change in human populations
What are the elements of Natural Selection?
- Differential success in reporudction: certain alleles being passed to next generation in greate proportions
- Brings adaptive evolution via acting on phenotype
- Relative fitness: contribution an indivudal makes to gene pool for next generation
What are the three modes of selection in relation to natural selection?
- Directional selection: **favors **individuals at one end of phenotypic range
- Disruptive selection: favors individuals at both ends of phenotypic range
- Stabilizing selection: acts against ends of phenotypic range, favors intermediate variants
