7b slides Flashcards
what is evolution at its finest level
change in allele frequencies in a population over generations
what are the three main mechanisms that cause allele frequency change
-natural selection
-genetic drift
-gene flow
what is the only thing that causes adaptive evolution
adaptive evolution
adaptive evolution is
a process in which traits that enhance survival or reproduction tend to increase in frequency over time, resulting in a better match between organisms and their environment
gene pool
all the alleles in a population
what is a population a mix of
homozygous and heterozygous individuals
genetic drift
chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
random genetic drift
more beneficial or less beneficial trait may increase
what type of population are effects of genetic drift most obvious
small populations
what are the mehcnaisms of genetc drift
-founder effect
-bottleneck effect
when does genetic drift founder effect occur
when a few individuals become isolated from a larger population and form a new population
is the founder gene pool reflective of the original population
no
bottleneck effect
genetic drift that occurs when the size of a population is reduced randomly
How is natural selection more “predictable” than genetic drift?
Natural selection is more “predictable” in that it alters allele frequencies in a nonrandom way: It tends to increase the frequency of alleles that increase the organism’s reproductive success in its environment and decrease the frequency of alleles that decrease the organism’s reproductive success. Alleles subject to genetic drift increase or decrease in frequency by chance alone, whether or not they are advantageous.
gene flow
The transfer of alleles from one population to another due to movement of fertile individuals or their gametes
gene flow tends to _______ variation ________ populations and _______ variation _______ a population
reduce/between
increase/within
what does natural selection result in
alleles being passed to the next generation in proportions that differ from those in the present generation in a nonrandom way
Why is natural selection the only mechanism that consistently leads to adaptive evolution in a population?
Although both gene flow and genetic drift can increase the frequency of advantageous alleles in a population, they can also decrease the frequency of advantageous alleles or increase the frequency of harmful alleles. Only natural selection consistently results in an increase in the frequency of alleles that enhance survival or reproduction. Thus, natural selection is the only mechanism that consistently leads to adaptive evolution.
what are the three general modes of natural selection that affect quantitative trait/character
-directional selection
-disruptive selection
-stabilizing selection
who does directional selection favor
individuals at one extreme end of the phenotypic range
Quantitative trait/character
A heritable feature that varies continuously over a range rather than in an either-or fashion
who does disruptive selection favor
individuals at both extremes of the phenotypic range
who does stabilizing selection favor
intermediate variants and acts against extreme phenotypes
what does stabilizing selection reduce
variation, acts against extreme phenotypes
sexual dimorphism
marked the differences between the sexes in secondary sexual characteristics
example of organisms that exhibits sexual dimorphism
elephant seal
secondary sexual charcateristics
characteristics not directly involved in reproduction
which is usually the showier sex
males
intrasexual selection
competition among individuals of one sex (usually males) for mates of the opposite sex
intersexual selection (aka mate choice)
individuals of one sex (usually female) are choosy in selection of mates
intra
within
inter
between
what does the good genes hypothesis suggest
suggests that if a phenotype is correlated with “good genes” (e.g., larval survival), both the male trait and female preference for that trait should increase in frequency
is their a benefit to females under the good genes hypothesis
no direct benefit to the female for her choice under this hypothesis, only her offspring
when does balancing selection occur
when natural selection maintains stable frequencies of two or more phenotypic forms in a population
what do balancing selection mechanisms include
-frequency dependent selection
-heterozygote advantage
what does the fitness of a phenotype depend on for frequency dependent selection
on how common it is in the population
when does heterozygote advantage occur
when heterozygotes have a higher fitness than both homozygotes
4 reasons why natural selection cannot fashion perfect organisms
- Selection can act only on existing variations
- Evolution is limited by historical constraints
- Adaptations are often compromises
intersexual selection/mate choice - Chance, natural selection, and the environment interact
what can hardy Weinberg equation be used to test
whether a population is evolving
Hardy-Weinberg equilibrium serves as
a baseline for comparison to data collected from a population
what does it mean when there is no difference with Hardy-Weinberg equilibrium
population is not evolving
what does it mean when there is a difference with Hardy-Weinberg equilibrium
population is evolving
