Exam II - Chapter 6 Flashcards
a situation in which allele and genotype frequencies in an ideal population do not change from one generation to the next
the hardy-weinberg equilibrium
hardy-weinberg theorem relies on these 5 assumptions:
No selection No mutation No migration No genetic drift (chance events) When random mating occurs
when alleles are not in equilibrium
evolution is occurring
Hardy-weinberg is violated (evolution occurs) when
there is: selection
there are: mutations, migration, chance events, mates are not chosen at random
serves as the fundamental null model of population genetics
hardy-weinberg theorem
when all alternative alleles have disappeared
fixed allele
when does fixation occur
when all individuals are genetically identical at a locus - happens in small populations
differential reproductive success that happens for a reason
selection
differential reproductive success that just happens; non-selection, random form of evolution; does not lead to adaptation
genetic drift
change in frequencies of allele copies in populations resulting from sampling error in drawing error in drawing gametes from gene pool to make zygotes and from chance variation in the survival and/or reproductive success of individuals; resulting in non-adaptive evolution
genetic drift
genetic drift results in a loss of heterozygosity- how is this for evolution?
heterozygosity –> good for evolution
homozygosity –> bad for evolution
M&M example
sampling error
(Graphs in book pg. 162 and quiz question) the smaller the population the _________ the genetic drift and the more variable the ______ frequency
stronger, more variable allele frequency (all over chart) where as a larger pop stays more steady
example of population bottleneck
northern elephant seals
events in which the number of individuals in a population is reduced drastically, even if the dip in numbers is temporary, it can have lasting effects on the genetic variation of a population
genetic bottleneck
could be a big problem for bottlenecks that lack genetic diversity
disease - could wipe out entire species
___ alleles are most likely to be lost during population bottle neck
rare (figure 6.9 page 164)
a type of genetic drift describing the loss of allelic variation that accompanies founding of a new population from a very small number of individuals
founder effect
can cause the new population to differ considerable from the source population
the success of an organism at surviving and reproducing and thus contributing offspring to future generations
fitness
the success of the genotype at producing new individuals (its fitness) standardized by the success of other genotypes in the population
relative fitness (of a genotype)
example of founder effect
silvereye birds: started in mainland Australia and then traveled from island to island and lastly ended in Norfolk island. the most diversity and genetic alleles on the mainland and the least on norfolk island (where they are most likely to go extinct
selection that decreases the frequency of alleles within a population; occurs whenever the average excess for fitness of an allele is less than zero
negative selection
selection that increases the frequency of alleles within a population; occurs whenever the average excess for fitness of an allele is greater than zero
positive selection
the condition when a mutation in a single gene affect the expression of many different phenotypic traits
pleiotropy
occurs when the effects of an allele at one genetic locus are modified by alleles at one or more other loci
epistasis
alleles that yield twice the phenotypic effect when two copies are present
additive allele
rare genotypes have higher fitness than common genotypes; this process can maintain genetic variation within populations
negative-frequency dependent selection
quiz question a type of genetic drift describing the loss of allelic variation that accompanies formation of a new population
founder effect
quiz question occurs when the effects of an allele at on locus are modified by alleles at one or more other loci
epistasis
quiz question selection that favors more than one allele; it acts to maintain genetic diversity
balancing selection
quiz question this is when rare genotypes have higher fitness than common genotypes; this process can maintain genetic variation in a population
negative frequency-dependant selection
quiz question an allele that yields twice the phenotypic effect when 2 copies are present at a given locus than when only a single copy is present is known as an
additive allele
example of negative frequency-dependent selection
elderflower orchid: some dark purple, some yellow; produce no nectar but trick bees- when bees land they take orchids pollen with them; risk-bees that visit orchids with no pollen (reward) can learn to avoid them
what does it mean when elderflower orchids “leapfrog” color frequencies
when purple color is low and yellow high - bees learn to avoid yellow b/c no pollen and go to purple more often
then purple become more predominant and the opposite happens. keeps going back and fourth
fitness is better when more rare color
selection that favors more than one allele; it acts to maintain genetic diversity in a population by keeping alleles at frequencies higher than would be expected by chance or mutation alone
balancing selection
examples of balancing selection
negative frequency-dependant selection, heterozygous advantage
what effect does natural selection have on deleterious mutations
it eliminates them
fox and gray squirrel polymorphism example
color difference; wanted white squirrels so killed gray squirrels but this was bad because it was reducing genetic diversity and thus increasing the chance of extinction
in the fox and gray squirrel example what was the big disadvantage of being white
many tumors found on white squirrels - UV damage
describe differences of being heterozygous and homozygous when it comes to sickle cell anemia?
AA - homo dominant; susceptible to getting malaria
AS - hetero - ADVANTAGE b/c you don’t have health problems from sickle cell and you also have protection from malaria
SS - homo recessive - health problems/lower fitness; suffer from sickle cell anemia
the probability that the two alleles at any locus in an individual will be identical by descent
inbreeding coefficient (F)
as inbreeding increases
survival decreases, deleterious genes increase
a reduction in the average fitness of inbred individuals relative to that of outbred individuals; it arises because rare, recessive alleles become expressed in a homozygous state where they can detrimentally affect the performance of individuals
inbreeding depression
what was the significance of the collard lizard example healthy vs actual populations and what were some ways to possibly fix it
healthy population should have many different genes, but it is found that separate populations have mostly only one or 2 genes each.
could bring outside females in, remove barriers, mix lizards around to other populations to mix genes, etc.
Genetic drift is non-selection, _____ form of evolution
Random
_____ are more greatly influenced by genetic drift than _____ populations.
Small populations; large
Genetic drift results in loss of
Heterozygosity
Genetic drift does NOT lead to _____, selection does.
Adaptation
A _____ population goes extinct more readily.
Small population
_____ is higher with a smaller sample
Sampling error
Genetic drift results from random _____
Sampling error
In a small population, there is a higher chance all alleles _____, despite how common.
All alleles lost
_____ will be more likely to occur on mainland
Evolution
Population more likely to _____ on norfolk
Go extinct
When a gene has a frequency higher than normal, that indicates
Sampling error (founder effect)
Recessive will be slower to fix. Why?
Heterozygotes will not show phenotype and will take a while for homozygotes to appear. Once they do, seelction will quickly carry it to fixation
Some forms of selection maintain diversity in populations. For example?
Negative frequency-dependent selection
Drift more powerful in _____ population. Selection more powerful in _____ population.
Drift - small
Selection - large
Inbreeding depression results in _____
Reduced fitness
As F increases, survival _____ and deleterious genes _____
Survival decreases, deleterious genes increase
