Chapter 22,23 Flashcards
what is a species?
organisms that can interbreed in nature
what is a gene pool?
all the alleles present in all individuals in the same species
what is a population?
interbreeding group of organisms of the same species living in the same geographical area
what is evolution?
the change in allele/genotypic frequency in a population over time
what is fitness?
the relative reproductive ability of an individual
what is a monophyletic group?
a group of organisms that descended from the same common ancestor
what is adaptation?
inherited traits that were shaped by natural selection and that promote survival and reproduction
what can cause changes in allele/genotype frequencies?
factors such as mutations, gene flow, genetic drift, natural selection, and nonrandom mating
What does genetic variation in a population depend on?
the rates of occurrence of the alleles in the population i.e allele frequency
how do mutations cause changes in allele/genotype frequencies?
creates new alleles through random nucleotide changes and recombination of genetic info
how does gene flow cause changes in allele/genotype frequencies?
- adds new alleles into populations they move into
- changes the frequencies of alleles already present in the population
How has gene flow become an important agent of evolutionary change in human populations?
increase in human migration (i.e gene flow) has led to mating between dissimilar populations, causing the exchange of alleles and fewer genetic differences between those populations (amalgamation)
how does natural selection cause changes in allele/genotype frequencies?
certain individuals have better fitness than others and these individuals with their genotypes produce more offspring, therefore leading to adaptation
what does natural selection require for it to cause evolution?
a diverse population is needed for differential survival and reproduction to occur, a population of clones will have same fitness all around and will therefore be unable to adapt and evolve
what is natural selection?
differential survival and reproductive success between individuals
When can natural selection lead to evolution?
If genotypes differ in average fitness, then some genotypes that have better fitness relative to others will contribute more alleles to future generations
what are the three patterns of natural selection?
- stabilizing
- directional
- disruptive
what is stabilizing selection?
natural selection that selects against the extreme phenotypes/ selects for the mean
what is directional selection?
natural selection that selects against one of the two extreme phenotypes
what is disruptive selection?
natural selection that selects against the mean/ selects for the extremes
Why does disruptive selection have the potential to create new species?
disruptive selection drives the extremes of a population apart, leading to speciation because of the divergence and isolation between the two extremes.
what is artificial selection?
successful genotypes are selected by the breeders (usually humans), not by nature or by competition
what form of selection is artificial selection?
Directional selection because artificial selection selects against one of the extremes and selects for the other
what is sexual selection?
a form of natural selection in which individuals with certain characteristics are more likely to mate and reproduce than other individuals (more attractive)
what is sexual dimorphism?
when males and females show distinctly different appearances
How does sexual selection lead to sexual dimorphism?
the more attractive organisms are able to pass on their alleles to their offspring while the less attractive ones die off
What form of selection can counteract sexual selection?
natural selection, more attractive organisms may have decreased fitness in order to be more attractive to opposite sex
How does genetic drift cause changes in allele/genotype frequencies?
some individuals may by chance leave behind more descendants (and genes) than other individuals
why are small populations more susceptible to genetic drift?
small populations have less individuals to randomly sample alleles from
what are the two forms of genetic drift?
- Founder Effect
- Population Bottleneck
what is the founder effect?
a small group leaves a large population and starts a new population, with random genes and alleles present in the new population that doesn’t necessarily represent the allele/genotypic frequency of the large population
what is population bottleneck?
a large population shrinks to a small number of individuals by chance (mass death, natural disaster) which reproduce to repopulate
why can genetic drift lead to loss of genetic variation?
genetic drift causes allele frequencies to change at random, meaning some alleles can be lost no matter they have on fitness
How does nonrandom mating cause changes in genotype frequencies?
nonrandom mating leads to nonrandom allele combinations, changing the population’s genetic structure
what are the types of nonrandom mating?
- Assortative mating
- Disassortative mating
what is assortative mating?
mating between parents that are genetically or phenotypically similar, leading to offspring being genetically similar
what is disassortative mating?
mating between parents that are genetically or phenotypically different, leading to offspring being genetically different
How does nonrandom mating affect a population’s genetic structure?
- assortative mating leads to excess homozygotes
- disassortative mating leads to excess heterozygotes
explain how diversity is impacted by mutations
increases diversity within populations
explain how diversity is impacted by gene flow
increases diversity within populations
decreases diversity between populations (amalgamation)
explain how diversity is impacted by natural selection
usually decreases diversity within populations (adaptation)
can increase or decrease diversity between populations (speciation, convergent evolution)
explain how diversity is impacted by genetic drift
decreases diversity within populations
increases diversity between populations (speciation)
what is the Hardy-Weinberg equilibrium?
type of equilibrium in populations that have constant allele and genotype frequencies from generation to generation because they are not evolving
what are the conditions for a population to be in Hardy-Weinberg equilibrium?
absence of evolutionary influences:
- no mutations
- no gene flow
- no natural selection
- no genetic drift
- random mating
therefore, change will not happen and alleles will combine into genotypes based on the laws of probability
what is the Hardy-Weinberg equilibrium good for?
if a population is in Hardy-Weinberg equilibrium, we can compute the frequencies of genotypes from the allele frequencies because p and q do not change
what is the Hardy-Weinberg equilibrium equation?
p + q = 1 (allele frequency)
p² + 2pq + q² = 1 (genotypic frequency)
a population is not at equilibrium if equation does not equal 1
