Chapter 21: Evolution Flashcards
define evolution
any change in allele frequency, genotype frequency, OR both constitutes evolution
how do new alleles appear?
ONLY through mutation –> mutation makes new genes
what does gene recombination do?
shuffles mutations to produce new sequences
define locus
location of a gene on a chromosome
what is the formula to find allele frequency?
(# copies of an allele) / (total # of alleles in a population)
what drives evolution?
natural selection
what drives natural selection?
genetic variation
define species
individuals that can exchange genetic material through interbreeding
define gene pool
all of the alleles present in all individuals of a single species
define population
interbreeding group of organisms of the same species living in the same geographical area
what are the two sources of genetic variation?
mutation and recombination (in both cases, new alleles are formed)
define mutation
generates NEW variations in genes (new alleles)
define recombination
shuffles gene mutations to make new combinations of mutations
what are the two places where mutations occur?
somatic (occur in body tissues)
germ-line (occur in reproductive cells and are passed on)
what are the 3 types of mutations?
deleterious
neutral
advantageous
define “adapted”
better able to survive and reproduce in a particular environment
define allele frequency
rtes of occurrence of alleles in populations
what does it mean when a population is “fixed” for an allele?
when a population only exhibits one allele at a particular gene (no other genetic option besides that one allele)
when allele frequency is 1
what are 3 ways we can measure genotype and allele frequencies in populations?
observable traits
gel electrophoresis
DNA sequencing
define phenotype
observable traits
-a product of the genotype and the environment
define Hardy-Weinberg equilibrium
the situation in which evolution does not occur
what are the requirements for the Hardy-Weinberg equilibrium? (5)
- everyone has same chance of surviving/reproducing
- no migration, must be a closed society
- no mutations
- must be a large enough population to avoid sampling errors
- individuals must mate at random (no sexual preferences)
define non-random mating
when individuals do not mate at random
- sexual preferences
- affects genotype frequencies, but not allele frequencies
what are the results of natural selection?
increases the frequency of beneficial alleles, resulting in adaptation
change in allele frequencies from generation to generation according to the allele’s impact on survival/reproduction of the individuals that hold that allele
define competitive advantage
a function of how well an organism is adapted to its environment
what does it mean if an organism is more “fit”? define fitness
a measure of the extent to which an individual’s genotype is represented in the next generation
(more fit, able to reproduce and survive and pass on genotype to offspring)
define a “discrete” trait
a trait that is either/or
(ex. yellow or green) no in between
define a “continuous” trait
a variation that occurs across a spectrum
ex. height
define positive selection
when natural selection increases the frequency of a beneficial allele
define negative selection
when natural selection decreases the frequency of a deleterious allele
define balancing selection
when natural selection acts to maintain two or more alleles in a population at intermediate frequencies
heterozygote advantage
describes the case in which the heterozygote genotype has a higher relative fitness than either the homozygote dominant or homozygote recessive genotype.
(ex. people in Africa who carry one allele for sickle cell and one that is vulnerable to malaria. they do not develop the deadly sickle cell disease, but they are less likely to get malaria because they are heterozygous for that blood type)
define stabilizing selection
selects against extremes in a population
define directional selection
selects against one of two extremes in a population
define disruptive selection
selects against the mean in a population (results in extremes)
define artificial selection
a form of directional selection
-successful genotypes are carefully manipulated and reproduced by a breeder
define sexual selection
promotes traits that increase an individual’s access to reproductive opportunities
define migration
movement of individuals from one population to another, resulting in gene flow
define gene flow
the movement of alleles from one population to another
define genetic drift
the random change in allele frequencies from generation to generation
- leads to evolution
- does NOT lead to adaptation
- impact depends on population size
what is a population “bottleneck”
when a population falls to just a few individuals
define a “founder event”
when just a few individuals arrive to colonize an island and begin a new population (type of bottleneck)
define “molecular clock”
the correlation between the time two species have been evolutionarily separated and the amount of genetic divergence between them
define “pseudogene”
a gene that is no longer functional
