population evolution Flashcards
gene pool
all alleles available for all traits
changing gene frequency
alleles may become more or less common
natural selection drives evolution by
selecting the most fit individuals
evolution happens to ____, not ____.
populations, not individuals
2 ways of measuring genetic variation
- % of genes that are heterozygous
- Nucleotide differences between individuals (many may be neutral)
genetic variation: 4 sources
- making new alleles via mutations
- +/-/rearranging genes
*rapid reproduction
*sexual reproduction
mutations are almost always
bad
when would a mutation be neutral?
protein instructions are identical or similar OR change is in noncoding DNA
how does rapid reproduction lead to more genetic variation?
rapid reproduction means inter-generation mutations are more common
how does sexual reproduction lead to more genetic diversity?
it combines traits in new ways
genetic diversity:
how many alleles are in a population
population with HIGH genetic diversity:
-many genes have more than 1 version
-many gene combinations for new individuals
population with LOW genetic diversity:
-most genes have 1 version
-much fewer gene combinations for new individuals
natural selection requires …
genetic diversity
fixed allele
single version of gene in entire population
allele frequency
how common an allele is in a population
hardy Weinberg equilibrium tests if
natural selection is happening or not
hardy Weinberg equilibrium predicts
frequency of genotypes in the next generation. at equilibrium, genotype frequency does NOT change.
Hardy Weinberg equilibrium assumes:
-no new alleles (mutations)
-random mating
-no natural selection
no genetic drift (large population)
-no gene flow (no individuals leave or enter)
*NO equilibrium if one of these is untrue
Hardy Weinberg equilibrium is not met if
allele frequencies change
most common reasons allele frequency changes:
-genetic drift
-gene flow
-natural selection
genetic drift:
RANDOM CHANCE INFLUENCES ALLELE FREQUENCY
genetic drift (change in allele frequency due to random chance) can lead to:
-rapid changes in allele frequency/traits
-permanent loss of alleles in population
-cause harmful alleles to become fixed in population
genetic drift is most common in 3 situations
-founder effect
-bottleneck effect
-small population
founder effect:
gene pool of immigrants to new area does not match gene pool of source population (can cause rare genetic diseases)
bottleneck effect
gene pool of survivors after a disaster does not match the gene pool of the population before the disaster
example of bottleneck effect
nearly all cheetahs died, forcing closely related cheetahs to breed. Current cheetah population has a small gene pool
Increased diseases, poor sperm quality, high mortality
small population:
The failure of one individual to reproduce can dramatically change the gene pool of a small population
relative fitness
contribution to the next generation compared to others contribution
3 steps to confirm/test natural selection
- artificial selection
-natural selection in the lab
-natural selection in the wild
the modern synthesis
term for combination of evolution and genetics that started in the 30s
___ provided a basis for understanding how natural selection worked
genetics
natural selection favors mutations that give more ___
fitness
well adapted individuals contribute more ___ to next generation
offspring (unfavorable traits then decrease)
3 patterns of natural selection
- Stabilizing selection
- Directional selection
- Disruptive selection
stabilizing selection
average variant in a population has the highest fitness
stabilizing selection prevents …
a trait from changing in a population
direction selection causes
population traits to move in a specific direction
directional selection: one of the two extremes…
becomes more common
disruptive selection
most common variant has lowest fitness
disruptive selection leads to
a population with 2+ variants
stabilizing selection, direction selection, disruptive selection: which is most likely to form a new species?
disruptive selection (leads to a population with 2+ variants)
coevolution is when 2 species …
apply pressure on each other
coevolution often occurs in
predator-prey relationships
-deer are fast to escape wolf, so wolf has to get faster or else they starve, and then deer gets faster, etc
why don’t suboptimal alleles disappear?
balancing selection: natural selection favors maintaining multiple alleles in some circumstances
frequency dependent selection
fitness of allele depends on how common it is (being common reduces allele fitness)
heterozygous advantage?
some heterozygotes have higher fitness than homozygotes
why did Dodo go extinct?
mismatched adaptation
why is there a lot of concern with climate change occurring so rapidly?
adaptation takes time (many generations, not on lifetime)
