Week 2 Flashcards
What mechanism did Charles Darwin propose for evolution?
Natural Selection
What two factors contribute to a species phenotype?
1) an individual’s genotype, and:
2) the environment in which the individual lives
Define: genotype
The set of alleles possessed by the individual.
Define: species
A species consists of individuals that can exchange genetic material through interbreeding.
From a genetic perspective: a group of individuals capable, through reproduction, of sharing alleles with one another.
Define: population
Populations are interbreeding groups of organisms of the same species living in the same geographical area.
What are two sources of genetic variation?
1) mutation, and:
2) recombination
What is the difference between somatic and germ-line mutations?
Somatic mutations are mutations that occur in the body’s tissues - they only affect the individual, and germ-line mutations are mutations that occur in the reproductive cells - germline mutations are passed on to the next generation.
What are the three ways that we classify mutations based on their effects on an organism?
1) neutral, and:
2) deleterious, and:
3) advantageous
Define: neutral mutation
A mutation that has little or no effect on an organism.
Define: deleterious mutation
A mutation that has a harmful effect on an organism. These mutations usually occur in the protein-coding regions of the genome.
Define: advantageous mutation
A mutation that improves their carriers’ survival or reproduction. These mutations are the ones that result in a species that is adapted to its environment.
What does it mean when we say a population is fixed for an allele?
It means that the population only exhibits one allele at a particular gene.
What are the three ways in which we can measure genotype and allele frequencies?
1) observable traits, and:
2) gel electrophoresis, and:
3) DNA sequencing
How does the process of gel electrophoresis work?
Gel electrophoresis works by separating segments of DNA according to their size.
What is evolution?
Evolution in a change in allele or genotype frequency over time. Populations evolve, not individuals.
What does the Hardy-Weinberg equilibrium describe?
The Hardy-Weinberg equilibrium describes situations in which allele and genotype frequencies do not change.
What does it mean when a population is at Hardy-Weinberg equilibrium?
When a population is at Hardy-Weinberg equilibrium, it means that evolutionary forces are not acting on the gene in the population we are studying - evolution is not taking place!
What are the five conditions that satisfy the Hardy-Weinberg equilibrium?
1) no natural selection
2) no immigration or emigration
3) no mutations
4) large population size
5) mating must be random
What can we infer when a population is not in Hardy-Weinberg equilibrium?
That evolution has occurred.
What are the primary mechanisms of evolution?
1) selection
2) migration
3) genetic drift
4) mutation
5) non-random mating
What is the underlying mechanism of adaptation?
Natural Selection
As well as Darwin, who also created/discovered the idea of natural selection as a mechanism of adaptation?
Alfred Russel Wallace
Why are population sizes typically said to be stable?
- not enough resources available, limits population growth
- competition for resources takes place
Define: modern synthesis
Theory that combines Mendelian genetics and Darwinian evolution.
- extends Mendel’s theory to include multiple genes per trait
Define: positive selection
Natural selection that increases freq. of favorable alleles.
Define: negative selection
Natural selection that decreases the freq. of a deleterious allele.
Define: balancing selection
Natural selection that acts to maintain two or more alleles in a population.
Define: stabilizing selection
Maintains status quo, acts against extremes.
Define: directional selection
Selection that leads to change in a trait over time.
Define: artificial selection
Another method of directional selection, competitive element is removed, successful genotypes chosen by the breeder.
Define: disruptive selection
Selection that acts in favor of the two extremes.
Define: sexual selection
Selection that acts to emphasize and promote traits that increase an individual’s access to reproductive opportunities.
Define: intrasexual selection
Focuses on interactions between individuals of the same sex (males vs. males).
Define: intersexual selection
Focuses on interactions between individuals of the different sexes (males vs. females).
How does migration affect populations?
- increases gene flow
- may be maladaptive, can decrease the fitness of a population
Define: bottleneck
Large population goes down to just a small # of individuals.
Define: founder effect
A few individuals start a small population.
What are some key points of genetic drift?
- doesn’t lead to adaptations
- impact of GD depends on population size (small populations more rapidly effected and vice versa)
How does non-random mating affect a population?
- changes genotype frequencies but allele frequencies remain the same
Define: inbreeding depression
A reduction in an offspring’s fitness caused by homozygosity of deleterious recessive mutations.
Define: molecular evolution
Populations that have diverged genetically.
Define: molecular clock
Correlation between the time two species have been separated and the amount of genetic divergence between them.
What are some key points on molecular clocks?
- rate of molecular clock vary from gene-gene
- clock set using fossil record
What gene has the slowest molecular clock?
Histone Genes
Define: pseudogene
A gene that is no longer functional.
What gene(s) have the fastest molecular clocks?
Pseudogenes
