exam 3 ppt 8 Flashcards
5 assumptions of HWE
mate at random, no natural selection, no genetic drift, no gene flow, no mutation
what was charles darwin’s book on evolution?
On the Origin of Species (about natural selection)
what did Darwin and Wallace do?
they independently came to describe natural selection
definition of artificial selection
describes how humans have modified species for desired traits over many generations
which type of selection is due to human manipulation?
artificial selection
what did Darwin base his theory called natural selection on?
he based it on the principles of artificial selection
definition of fitness
those best adapted to an environment would be most successful at passing on their genes to the next generation
what does natural selection do?
natural selection acts over generations to increase the fitness of a population
definition of adaptation
any heritable trait that increases the fitness of an individual relative to those lacking the trait
did Darwin and Wallace ultimately publish together?
yes
how many postulates does natural selection have?
4
4 postulates of natural selection (listed)
1) variation exists in populations, 2) some of the differences in traits are heritable, 3) survival and reproductive success is variable, 4) the individuals that have the highest survival and the highest number of offspring are not random
1st postulate of natural selection
variation exists in populations
2nd postulate of natural selection
some of the differences in traits are heritable
3rd postulate of natural selection
survival and reproductive success is variable
4th postulate of natural selection
the individuals that have the highest survival and the highest number of offspring are not random
what is another name for natural selection?
survival of the fittest
definition of survival of the fittest (natural selection)
the more prolific reproduction of individuals with favorable traits (adaptations) that survive environmental change because of those traits; this leads to evolutionary change
what different characteristics can natural selection be?
it can be stabilizing, directional, or diversifying- acting on a phenotype
definition of directional selection
changes the average phenotype of a population in one direction (skewing one way or another)
definition of stabilizing selection
reduces both extreme phenotypes in a population
definition of disruptive selection
eliminates average phenotypes and favors extremes
definition of balancing selection
maintains variation in the population; no phenotype is favored; favors variation
exp of disruptive selection
beak length in Darwin’s finches- only birds with short or extremely long beaks survived long enough to reproduce (intermediates didn’t have any food to eat in drought, died)
could selection lead to the formation of a new species?
yes
in directional selection, genetic variation is…
reduced
in stabilizing selection, genetic variation is…
reduced
in disruptive selection, genetic variation is…
increased (selecting for two different phenotypes, the extremes)
in balancing selection, genetic variation is…
maintained
natural selection works by acting on ….
genetic variation
as a result of natural selection acting on phenotypic variation, the _______ also changes
frequency of alleles
exp of how the frequency of alleles changes with natural selection
rock pocket mice- increase for dark fur, decrease for light fur
huntington’s disease is caused by a dominant lethal mutation, the allele H. if having the H allele leads to death, what would you expect to see happen to the H allele over time?
the allele is still in human population because it doesn’t show up until age 30-40; if stopped during reproduction, it wouldn’t survive still
what may occur in extreme cases of natural selection?
fixation
definition of fixation
in natural selection, may occur where a beneficial allele has a frequency of 1 (other allele frequency is 0, only one allele present)
definition of positive selection
increases the frequency of a favorable allele
exp of positive selection
B allele in lava flow areas- rock pocket mice
definition of negative selection
decreases the frequency of a harmful allele
exp of negative selection
b allele in lava flow areas
definition of balancing selection
observed when two alleles are maintained, and are more successful in different conditions (either allele can be helpful)
what can be one explanation for balancing selection?
heterozygote advantage
definition of heterozygote advantage
occurs when heterozygotes have a higher fitness than do both homozygotes
exp of heterozygote advantage
in tropical Africa, where Malaria is common (parasite attacks red blood cells): 1) homozygous wild type individuals die of malaria (SS), 2) homozygous recessive individuals die of sickle cell anemia (ss), 3) heterozygotes are relatively free of both (Ss)- cancels each other out
definition of sexual selection
promotes traits that increase an individual’s reproductive fitness, and may seem to violate natural selection
type of sexual selection
sexual dimorphism
definition of sexual dimorphism
distinct difference in size or appearance between the sexes of an animal in addition to differences between the sexual organs themselves; leads to them being more relroductively successful
exp of sexual dimorphism
birds- color, feathers of males vs females, etc
two broad types of sexual selection
intersexual selection, intrasexual selection
definition of intersexual selection
(between two sexes) occurs when a mate is chosen by an individual of the opposite sex
definition of intrasexual selection
(within a sex) occurs when there is a competition to obtain a mate
exp of intrasexual selection
red deer males use weaponry with their antlers to compete for mates
exp of intersexual selection
male birds of paradise display their feathers for females
what is sexual selection an example of?
natural selection
the varied traits we discussed are examples of…
adaptations
what is the only “adaptive” type of evolution?
natural selection
what types of evolution are non-adaptive?
mutation, genetic drift, and gene flow
