Ch.23: Evolutionary Processes Flashcards
Processes that drive evolution
natural selection, genetic drift, gene flow, and mutations
Gene Pool
population made up of individuals of the same species and includes all genes and combinations of genes in the population
Assumptions of Hardy-Weinberg Model
no natural selection, no genetic drift, no gene flow, no mutations, and random mating
What is HWP used to test?
It is used to test the hypothesis that no evolution is occurring at a particular gene and that in the previous generation, mating was random with respect to the gene in question
used to test microevolution
How would you know if a population is evolving?
look for changes in the gene pool and follow the population’s gene frequencies over time and look for changes
Hardy-Weinberg Theorem
frequencies of alleles and genotypes in a population’s gene pool remain constant over generations unless acted upon by another agent other than sexual recombination
Microevolution
generation to generation change in a population’s genetic structure
small scale evolutionary change
Modes/patterns of natural selection
directional, stabilizing, disruptive, and balancing selection
Directional Selection
- tends to reduces genetic variation
- favours one extreme phenotype and causes the average phenotype of the trait to change
- ex. during cold weather -> cliff swallows
Stabilizing Selection
- tends to reduce genetic variation
- favours the average phenotype
- there is no change in average value of a trait over time
- ex. birth weight in babies
Disruptive Selection
- tends to increase genetic variation
- favours the most extreme phenotypes and eliminates phenotypes near the average value
- ex. birds that eat large and small seeds
Balancing Selection
- no allele has a distinct advantage
- there is balance in terms of fitness and frequency
- occurs due to heterozygote advantage and frequency-dependent selection
Heterozygote advantage
heterozygous individuals have higher fitness than homozygous individuals
Frequency-dependent selection
certain alleles are favoured when they are rare, but not when they are common
Genetic Drift
any change in allele frequencies in a population due to chance
undirectional and random
caused by founder effects and genetic bottlenecks
Founder effect
change in allele frequencies that occurs when a new population is established
Genetic bottleneck
sudden reduction in the number of alleles in a population
Which of the modes of selection may lead to speciation?
disruptive selection
Gene flow
movement of alleles between populations when an individual leaves one population, joins another and breeds
movement of alleles between populations tends to reduce their genetic differences
Sampling Error
the idea that allele frequencies change due to blind luck when drift occurs
How are new alleles formed?
mutations
three ways in which mutations can occur as
point mutations, chromosome-level mutations, and lateral gene transfer
Evolution cannot occur without __________.
mutations
Deleterious alleles
alleles that lower fitness and tend to be eliminated by purifying selection
Beneficial alleles
alleles that allow individuals to produce more offspring
very rare
Neutral alleles
- allele with not effect on fitness
- occurs when point mutation is silent
three mechanisms that violate HW assumption of random mating
inbreeding, assortative mating, and sexual selection
Inbreeding
- mating between relatives
- increases homozygosity and decreases heterozygosity
- can speed the rate of evolutionary change (i.e. increases rate at which natural selection can eliminate the recessive deleterious alleles from population)
What is the most extreme form of inbreeding?
self-fertilization
Inbreeding depression
decline in average fitness that takes place when homozygosity increases and heterozygosity decreases
Assortative Mating
takes place when mating is nonrandom with respect to specific traits
Positive assortment
individuals tend to choose mates that share a particular phenotype with them
Negative assortment
individuals tend to choose mates that differ in specific phenotypic trait
Sexual selection
occurs when individuals within a population differ in their ability to attract mates
Intersexual selection
selection of an individual of one gender for mating by an individual for another
Intrasexual selection
form of selection within a gender in which individuals sometimes compete with one another to obtain mates
Fundamental Asymmetry of Sex
females invest much more in offspring than males
Why should sexual selection act more strongly on males than females? Use Bateman-Trivers theory predictions to explain.
Females fitness is limited by its ability to gain resources for its offspring while males fitness is limited by the number of females he can mate with. Females can be choosy in terms of who they want to mate with and as a result males need to compete with each other to gain females to mate with.
three factors that females may choose mates based on
- physical characteristics that indicate male genetic quality
- behavioural characteristics that indicate their ability to provide parental care
- both
Sexual dimorphism
any trait that differs between males and females
