BCOR 102: Exam 4 Flashcards
classical model
“mendel’s model”
genetic variation is low
alternative alleles are rare, recessive, deleterious
Balance model
low levels of genetic variation but selection favoring heterozygosity
Neutral model
homozygous or heterozygous has no benefits or harmful effect from each other
(most alleles are neutral)
single nucleotide polymorphism (SNP)
Point mutation
can be beneficial or detrimental
silent mutation
does not change amino acid sequence
neutral mutation
change amino acid sequence, but not protein function
start/stop mutation
often lethal, codes a premature stop codon which ends a polypeptide early
Frameshift mutation
an inserted or deleted nucleotide, resulting in a shift in the reading frame
u (meuw)
mutation rate (mutations/gene locus/generation)
q(v)t : frequency of B allele after t generations
qt = 1 - Poe^(-ut)
q(v)o
1-Po
q-hat (for back mutation)
u/(u+v)
p-hat (for back mutation)
v/(u+v)
Po (migration)
initial allele frequency in resident population
Pm (migration)
frequency of allele in migrant population
m
migrant fraction
the proportion of population consisting of new migrants each generation
1-m
resident/fraction
proportion consisting of non-migrants
Pt equation
(1-m)^t (Po-Pm) + Pm
one-way migration
can lead to changes in local allele frequency
two-way migration
genetic homogeneous
random mating
mate choice is independent of genotype
positive assortative mating
more frequent mating between similar phenotypes
negative assortative mating
more frequent matings between dissimilar phenotypes
inbreeding
more frequent matings between close relatives
inbreeding coefficient (F)
1 - (H/Ho)
probability that 2 alleles in an individual are identical by descent from 1 ancestor
Ho
expected heterozygosity with random mating (2pq)
H
observed heterozygosity in the population
Autozygous alleles
2 alleles in an individual that are identical by descent from a single ancestor
allozygous alleles
2 alleles in an individual are identical by descent from 2 different ancestors
cost of inbreeding (short term)
increased expression of deleterious recessive alleles
cost of inbreeding (long term)
loss of heterozygosity
Benefits of inbreeding
preservation of a “coadapted” gene complex
Genetic drift
changes in allele frequency due to random segregation of alleles in small population (when N < 100)
N(v)E
effective population size vs N: total population size
Effective population size
= equivalent number of individuals in a truly random mating population
Founder effect
a population is colonized by only a few individuals –> carry a small number of alleles
bottleneck
a population that temporarily shrinks in size
Unbalanced sex ratio (N(v)E equation)
N(v)E = ((4)(Nm)(NF))/(NM + NF)
Limited dispersal (NE equation)
NE = 4(pi)(d)(x)
d = density (# of indiv./area)
x = dispersal distance from the place of birth to the place of mating
Four Horsemen (Mutation)
change in allelic freq. = yes (unlikely)
change in genotype freq. = yes (unlikely
strength of change = weak
fixation = yes (unlikely; no with back mutation)
new alleles = yes
predictable = yes
Four Horsemen (Migration)
change in allelic freq. = yes
change in genotype freq. = yes
strength of change = strong
fixation = yes
new alleles = yes
predictable = yes
Four Horsemen (Non-random mating)
change in allelic freq. = no (yes with recessive lethals)
change in genotype freq. = yes
strength of change = weak
fixation = no (yes with recessive lethals)
new alleles = no
predictable = yes
Four Horsemen (Genetic drift)
change in allelic freq. = yes
change in genotype freq. = yes
strength of change = strong
fixation = yes
new alleles = no
predictable = no (chance process)
tautology
self-referencing definition
ex. “survival of the fittest”
Natural selection
differential survival (and/or reproduction) of individuals with heritable traits
Assumptions of Natural Selection
- Individuals exhibit variation in their traits
- At least some of that variation has a heritable component
- All individuals produce more offspring than can survive
- Particular trait variance enhance survival in particular environments
Model of Natural Selection and Random Mating (7 Steps)
- Given (initial genotype counts and relative fitness values of each genotype)
- Calculate initial genotypic and allelic frequencies in a population (Po, qo)
- Calculate genotypic frequencies AFTER random mating
- Calculate genotype frequencies AFTER selection
- Normalize genotype frequencies (sum of the genotype frequencies is 1)
- Calculate new allele frequencies (P1 and Q1)
- Calculate new genotype frequencies after random mating
Mean fitness
average fitness of the individuals in the population after random mating and selection (w-bar)
selection coefficient
a measure of selection against a genotype
Fisher’s Fundamental Theorem of Natural Selection
natural selection maximizes w-bar
Modern synthesis
- Evolutionary phenomenon
- changes in allele frequencies
- evolution of adaptions
- speciation
- can be explained by mechanisms consistent with Mendelian inheritance - evolution is gradual
- Natural selection is strongest mechanism of evolution
- Genetic diversity in populations reflects current + past selection
- Microevolutionary change can lead to macroevolutionary responses
Co-adapted gene complex
A winning combination of alleles in a particular environment
Selection Scenario: Against a recessive allele
w1 = 1
w2 = 1
w3 = 1-s3
result: relatively slow elimination of B allele
w-bar = –>1.0
Final # of alleles: 1 allele (A)
Selection Scenario: Against a recessive lethal
w1 = 1
w2 = 1
w3 = 0
result: relatively slow elimination of B allele
w-bar = –>1.0
Final # of alleles: 1 allele (A)
Selection Scenario: aganist a recessive + mutation
w1 = 1
w2 = 1
w3 = 1-s3
result: equilibrium
w-bar = <1.0
Final # of alleles: 2 alleles
Selection Scenario: against a dominant allele
w1 = 1-s1
w2 = 1 - s2
w3 = 1
result: relatively rapid elimination of A allele
w-bar = –>1.0
Final # of alleles: 1 allele (B)
Selection Scenario: Favoring the heterozygote
w1 = 1-s1
w2 = 1
w3 = 1-s3
result: equilibrium
w-bar = <1.0
Final # of alleles: 2 alleles
