Chapter 27 Flashcards
get big ah smart
What is population genetics?
extent of genetic variation within a group of individuals and changes in that variation over time (focus shifted away from individual and toward population of which the individual is a member)
What is the gene pool?
All alleles of every gene in a population (only individuals that reproduce contribute to gene pool of next generation)
What is the goal of population geneticists?
Make predictions about how generations change due to genetic variation within the gene pool
What is a population?
group of individuals of the same species that occupy the same region and can interbreed with each other
What are local populations?
smaller groups within a population, often separated by moderate geographic barriers (ex: deer in ohio different from deer in new massachusetts)
What are three ways a population may change?
size, geographic location, genetic composition
What is polymorphism?
refers to observation that many traits display variation within a population (ex: Hawaiin happy-face spider that differ in alleles that affect color and pattern)
How can a gene be described that commonly exists as 2 or more alleles in a population?
Polymorphic
(monomorphic gene exists predominantly as a single allele)
What is a single-nucleotide polymorphism (SNP)?
A change in single base pair in DNA, SNPs account for 90% of variation among people, may not lead to change in phenotype
What is an example of SNP?
Sickle cell disease caused by a deletion that eliminates function
What is the equation for allele frequency?
Allele Frequency = (Number of copies of an allele in a population) / (Total number of alleles for that gene in a population)
What is the equation for genotype frequency?
Genotype frequency = (Number of individuals with a particular genotype in a population) / (Total number of individuals in a population)
Are polymorphisms common or rare in natural populations?
very common
What is the Hardy-Weinberg equation?
simple mathematical expression that relates allele and genotype frequencies in a population, also called an equilibrium (no evolution/change)
p^2 + 2pq + q^2 = 1
(p is dominant and q is recessive)
A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D?
0.24
The allele frequency of C is 0.4 and that of c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes?
0.48
Which of the following is a factor that, by itself, does not promote widespread changes in allele or genotype frequencies?
a. new mutation
b. natural selection
c. genetic drift
d. migration
e. nonrandom mating
a. new mutation
What are the five conditions required to reach equilibrium?
no new mutations, no genetic drift (no change of frequencies due to chance alone), no migration, no natural selection, random mating
What is the null hypothesis in HW equilibrium?
No change/evolution
If null hypothesis is not rejected, you can accept the hypothesis that the population is __________.
in equilibrium
If the null hypothesis is rejected, the population is __________.
in disequilibrium
What is microevolution?
describes changes in a population’s gene pool from generation to generation, driven by: mutation, random genetic drift, migration, natural selection, nonrandom mating (everything opposite HW)
In the theory of natural selection, phenotypes may vary with regard to their _____________.
reproductive success
What is fitness?
Measure of reproductive success in relative fitness values (ω), relative likelihood that a genotype will survive and contribute to gene pool of next generation
For calculating fitness values, the gene with the highest reproductive ability (most offspring) is given a fitness value of _____.
1.0
Does natural selection act on genotypes or phenotypes?
Phenotypes
Directional selection
Favors survival of one extreme phenotype that is better adapted to an environmental condition (choosing one phenotype as more fit)
Balancing selection
Favors maintenance of two or more alleles (heterozygote advantage)
Disruptive (or diversifying) selection & example
Favors survival of two (or more) different phenotypes
Caused by fitness values for a given genotype that vary in different environments
Example: snail that lives in woods (brown color favored on soil, pink shell favored on leaf litter) and open fields (yellow color favored)
Stabilizing selection & example
Favors survival of individuals with intermediate phenotypes
Tends to decrease genetic diversity
Example: laying eggs
Mean fitness of the population & equation
Measure of how fit the whole population is
p^2wAA + 2pqwAa + q^2waa = w (with bar on top)
Divide both sides by mean fitness and the equation will be set equal to 1 (slide 29)
Natural selection raises the _________ of the population from one generation to the next.
mean fitness
What is the selection coefficient equation
measures the degree to which a genotype is selected against
s = 1 - w
w is fitness
What is negative frequency-dependent selection?
type of balancing selection, rare individuals have a higher fitness than more common individuals; more likely to reproduce, selection always favors less numerous genotype
Name and example of frequency-dependent selection
Rewardless flower - relative fitness of the less-common flower increases
Genetic drift
random changes in allele frequencies due to random fluctuations, just chance based
Favors either loss or fixation of an allele
Less effect on large populations, rate depends on population size
Expected number of new mutations (genetic drift) equation
Expected number of new mutations = 2Nu (if each individual has two copies of the gene of interest)
u = mutation rate
N = number of individuals in population
New mutation more likely to occur in large populations
Probability of fixation of a newly arising allele due to genetic drift =
1/2N
What are the effects on mutations and fixations due to value of N in genetic drift?
Large N: new mutation more likely but has greater chance of being eliminated due to random genetic drift
Small N: new mutations less likely but has greater chance of being fixed in pop.
Equation for number of generations it takes for fixation
t (with line on top) = 4N
N is number of individuals in population assuming that males and females equally contribute
Bottleneck effect
Natural disaster randomly eliminates individuals regardless of phenotype
Founder effect
Small group of individuals separates from larger population and establishes colony in new location
2 important consequences:
founding population is expected to have less genetic variation than original pop., founding pop. will have allelic frequencies that may differ markedly from original pop. as matter of chance
Gene flow
Transfer of alleles from donor pop. to recipient pop., changing its gene pool
Recipient pop. called conglomerate
Equation for calculating change in allele frequency in conglomerate pop.
delta pc = m(pD - pR)
delta pc: change in allele frequency in conglomerate population
pD: allele frequency in donor pop.
pR: allele frequency in original recipient pop.
m: proportion of migrants in conglomerate pop.
m=(number of migrants in conglomerate pop.)/(total number of individuals in conglomerate population)
pc = pR +delta pc
Bidirectional migration
Tends to reduce allele frequency differences between populations and can enhance genetic diversity within population
Assortative mating (positive and negative)
Individuals don’t mate randomly
Positive - more likely to mate due to similar phenotypic characteristics
Negative - individuals with dissimilar phenotypes mate preferentially
Inbreeding
mating between genetically-related individuals, decreases overall diversity, gene pool smaller
Outbreeding
mating between genetically unrelated individuals
Inbreeding/fixation coefficient (F)
Degree of relatedness in pedigree, probability that gene in inbred individual is homozygous due to its inheritance from common ancestor
F = sum of ((1/2)^n (1+FA))
n: number of individuals in inbreeding path (excluding inbred offspring)
FA: breeding coefficient of common ancestor
Inbreeding example, frequencies of A and a are p and q
p^2 + fpq = frequency of AA
2pq(1-f) = frequency of Aa
q^2 + fpq = frequency of aa
Inbreeding depression
Inbreeding in natural populations will lower overall fitness
Ways to change genetic variation
syke
slide 75 has massive chart
Out of beneficial, neutral, and deleterious mutations, which is most likely?
Neutral and deleterious far likelier
Mutation rate
probability that a gene will be altered by new mutation
delta q = up
u: mutation rate of an allele into a different allele
q: allele frequency of new allele
p: allele frequency of current allele
To calculate the change in allele frequency after any number of generations:
(1-u)^t = pt/p0
u: the mutation rate of the conversion of original allele to new allele
t: the number of generations
p0: the frequency of original allele in the starting generation
pt: the frequency of allele original allele after t generations
Mutations are important fro evolution but has ______ impact in changes of allele frequency.
negligible
check slide 49
