Topic 3 Flashcards
natural selection
when there is variation within a population and organisms, and when that variation can be inherited, the variants best suited for growth and reproduction in a given environment will contribute disproportionately to the next generation
environmental variation
variation among individuals due to differences in environment
genetic variation
variation among individuals caused by differences in the genetic material that is transmitted from parent to offspring
“descent with modification”
evolutionary changes that have accumulated over time since the two lineages split
species
consists of individuals that can exchange genetic material through interbreeding
gene pool
all the alleles present in all individuals in the species
individuals represent different combinations of alleles drawn from:
the species’ gene pool
population genetics
the study of genetic variation in natural populations
population
interbreeding groups of organisms of the same species living in the same geographical area
what are the two sources of genetic variation?
mutation and recombination (synapsis)-produces new alleles
neutral mutations
having little or no effect-most common type of mutation because most of genome is noncoding DNA
deleterious mutation
harmful effect-most common type of mutation in coding sections of genome
advantageous mutation
improves carrier’s chance of survival or reproduction; least likely to occur
which type of mutation allows for adaptation of a species (better able to survive and reproduce in that environment)?
advantageous mutation
allele frequencies
rates of occurrence of alleles in population: number of allele x present in population divided by total number of alleles
a population is FIXED for that allele
=population exhibits only one allele at a particular gene
genotype frequency
the proportion in a population of each genotype at a particular gene or set of genes
what are three ways to measure genotype and allele frequencies in populations?
observable traits, gel electrophoresis, and DNA sequencing
observable traits require:
studies of traits/phenotypes that are encoded by a single gene
gel electrophoresis was applied to:
proteins to focus on enzymes and thus detect genetic variation, but can ONLY study enzymes
evolution is:
a change in allele OR genotype frequency over time (i.e. a change in the genetic makeup of a population over time)
Hardy-Weinberg equilibrium
describes situations in which allele and genotype frequencies do not change, they change only when specific forces act on the population
requirements to meet Hardy-Weinberg equilibrium:
- There can be no differences in the survival and reproductive success of individuals
- populations must not be added to or subtracted from migration
- there can be no mutation
- the population must be sufficiently large to prevent sampling errors
- individuals must mate at random
selection
the differential success of alleles
genetic drift
a change in the frequency of an allele due to the random effects of limited population size
non-random mating
individuals do not mate randomly, affects genotype frequencies from generation to generation but does not affect allele frequencies
the Hardy-Weinberg relation predicts:
genotype frequencies from allele frequencies and vice versa
what is the starting point for population genetic analysis?
the Hardy-Weinberg equilibrium-if population not in equilibrium, we can infer that evolution has occurred.
fitness
a measure of the extent to which the individual’s genotype is represented in the next generation
the Modern Synthesis combines:
Mendelian genetics and Darwinian evolution
what is the result of natural selection?
increased frequency of advantageous mutations (alleles), decreased frequency of deleterious mutations
positive selection
natural selection that increases the frequency of a favourable allele
negative selection
natural selection that decreases the frequency of a deleterious allele
how can deleterious alleles remain in the population?
the genetic disease may occur rarely only in homozygous genotypes, is not selected against when expressed as a heterozygote
balancing selection
maintenance of an allele at some intermediate frequency between 0-100%, maintains two or more alleles in a population
heterozygote advantage
an example of balancing selection in which the heterozygote’s fitness is higher than either of the homozygotes, resulting in selection that ensures both alleles remain in the population at intermediate frequencies, ex. malaria
stabilizing selection
maintains the status quo of phenotypes and acts against extremes; keeps a trait the same over time
directional selection
leads to a change in trait over time
artificial selection
a form of directional selection; analogous to natural selection but the competitive element is removed, instead, selection is done by breeder
disruptive selection
operates in favour of extremes and against intermediate forms, can lead to formation of new species
sexual selection increases:
an individual’s reproductive success
sexual selection
promotes traits that increase an individual’s access to reproductive opportunities; phenotypes are generally a trade-off between conflicting demands of reproduction and survival
intrasexual selection
focuses on interactions between individuals of one sex (ex. males compete with another for access to females)
intersexual selection
focuses on interactions between females and males (males do not fight one another but compete for attention of female, females choose their mates)
