Exam II - Chapter 6 Flashcards Preview

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Flashcards in Exam II - Chapter 6 Deck (60):
1

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

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hardy-weinberg theorem relies on these 5 assumptions:

No selection
No mutation
No migration
No genetic drift (chance events)
When random mating occurs

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when alleles are not in equilibrium

evolution is occurring

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Hardy-weinberg is violated (evolution occurs) when

there is: selection
there are: mutations, migration, chance events, mates are not chosen at random

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serves as the fundamental null model of population genetics

hardy-weinberg theorem

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when all alternative alleles have disappeared

fixed allele

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when does fixation occur

when all individuals are genetically identical at a locus - happens in small populations

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differential reproductive success that happens for a reason

selection

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differential reproductive success that just happens; non-selection, random form of evolution; does not lead to adaptation

genetic drift

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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

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genetic drift results in a loss of heterozygosity- how is this for evolution?

heterozygosity --> good for evolution
homozygosity --> bad for evolution

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M&M example

sampling error

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(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

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example of population bottleneck

northern elephant seals

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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

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could be a big problem for bottlenecks that lack genetic diversity

disease - could wipe out entire species

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___ alleles are most likely to be lost during population bottle neck

rare (figure 6.9 page 164)

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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

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the success of an organism at surviving and reproducing and thus contributing offspring to future generations

fitness

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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)

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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

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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

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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

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the condition when a mutation in a single gene affect the expression of many different phenotypic traits

pleiotropy

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occurs when the effects of an allele at one genetic locus are modified by alleles at one or more other loci

epistasis

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alleles that yield twice the phenotypic effect when two copies are present

additive allele

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rare genotypes have higher fitness than common genotypes; this process can maintain genetic variation within populations

negative-frequency dependent selection

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*quiz question* a type of genetic drift describing the loss of allelic variation that accompanies formation of a new population

founder effect

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*quiz question* occurs when the effects of an allele at on locus are modified by alleles at one or more other loci

epistasis

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*quiz question* selection that favors more than one allele; it acts to maintain genetic diversity

balancing selection

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*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

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*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

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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

34

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*

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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

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examples of balancing selection

negative frequency-dependant selection, heterozygous advantage

37

what effect does natural selection have on deleterious mutations

it eliminates them

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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

39

in the fox and gray squirrel example what was the big disadvantage of being white

many tumors found on white squirrels - UV damage

40

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

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the probability that the two alleles at any locus in an individual will be identical by descent

inbreeding coefficient (F)

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as inbreeding increases

survival decreases, deleterious genes increase

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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

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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.

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Genetic drift is non-selection, _____ form of evolution

Random

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_____ are more greatly influenced by genetic drift than _____ populations.

Small populations; large

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Genetic drift results in loss of

Heterozygosity

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Genetic drift does NOT lead to _____, selection does.

Adaptation

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A _____ population goes extinct more readily.

Small population

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_____ is higher with a smaller sample

Sampling error

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Genetic drift results from random _____

Sampling error

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In a small population, there is a higher chance all alleles _____, despite how common.

All alleles lost

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_____ will be more likely to occur on mainland

Evolution

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Population more likely to _____ on norfolk

Go extinct

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When a gene has a frequency higher than normal, that indicates

Sampling error (founder effect)

56

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

57

Some forms of selection maintain diversity in populations. For example?

Negative frequency-dependent selection

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Drift more powerful in _____ population. Selection more powerful in _____ population.

Drift - small
Selection - large

59

Inbreeding depression results in _____

Reduced fitness

60

As F increases, survival _____ and deleterious genes _____

Survival decreases, deleterious genes increase