Chapter 20 (Final) Flashcards
(40 cards)
Mendelian vs population genetics
Generations and relationships
Number of alleles analyzed
Influencing forces
Mode of reproduction
Generations and relationships
M = known
P = unknown
Number of alleles analyzed
M = 2 (usually)
P = variable (one to thousands)
Influencing forces
M = known + controlled
P = unknown + inferred
Mode of reproduction
M = known
P = known or unknown
Population
basic
a group of interbreeding organisms
Gene pool
the collection of genes and alleles found among members of a population
Population genetics
the study of allele frequencies and genotype frequencies within and between populations
Evolution
changes of allele frequency and genotype frequency over time
What is evolution influenced by (4 ex)
- mating patterns
- mutation rate
- genetic drift
- natural selection
etc
What is the Hardy Weinberg equilibrium model used for
- both independently concluded that random mating and absence of evolutionary change leads to stable allele frequencies in populations
model to calculate expected frequencies of alleles and genotypes of interest in large populations
H-W equilibrium - 6 assumptions
- Infinite population size
- Random mating within population
- No natural selection
- No migration/gene flow (no introduction of new alleles)
- No mutations (no introduction of new alleles)
- No genetic drift
H-W equilibrium - 4 predictions
- Allele frequencies remain stable over time
- Allele distribution into genotypes is predictable
- Stable equilibrium frequencies of alleles and genotypes are
maintained - Evolutionary and non-random mating effects are predictable
H-W equilibrium calculates expected genotype and allele
frequencies when evolution…
does NOT occur
Allele vs genotype frequency (calc)
For HW
Allele
p + q = 1
A1 + A2 = 1
Genotype
p^2 + 2pq + q^2 = 1
A1A1 + A1A2 + A2A2 = 1
Hardy-Weinberg Equilibrium for Two
Autosomal Alleles
Fixing vs max heterozygosity
When p = 1, one allele is fixed (no q)
When q = 1, other allele is fixed (no p)
Heterozygosity at highest frequency
when A1 = A2 = 0.5
2 methods to determine autosomal allele frequencies
And when to use each method; codom vs domrec
- Gene-counting method
* Requires genotypes of all members to be identifiable
* Useful for codominant alleles - Square root method
* Used when gene has two alleles with a dominant-recessive relationship
* Take square root of q2, then p is calculated as 1-q
HW for 3 alleles
Allele frequency
p + q + r = 1
Genotype frequency
(p+q+r)^2 = 1
six possible genotypes
p^2+q^2+r^2+2qr+2pq +2pr = 1
Natural selection
works through differential reproductive fitness and influences
genotype and allele frequencies of the next generation
Effect of natural selection
And relative fitness
When is mAx reproductive success
no longer HW equilibrium
Relative fitness (w) can quantify natural selection intensity
max reproductive success when w = 1
Selection coefficient (s)
Hint: It’s related to fitness
Individuals that reproduce less have their fitness decreased by a proportion called selection coefficient (s)
E.g, if individual A has a relative fitness of 1.0 and individual B has a relative
fitness of 0.8, the selection coefficient = 0.2
* Therefore, individual B reproduces 80% as well as individual A
Predicting genotypic and allelic frequency in the next generation
Predicting genotypic frequency in next
generation is equal to number of
individuals multiplied by relative fitness
- done for each genotype
Use gene-counting method to
calculate allele frequency in next
generation after selection
Gene counting method
For alleles
f(A) = [(2 x AAhomo survivors) + ABhetero survivors]
/
(total # survivors)
f(B) = [(2 x BBhomo survivors) + ABhetero survivors]
/
(total # survivors)
If strong selection intensity on an allele
What type of selection
directional selection
allele can become fixed over time
or v.v for lethal alleles
Recessive lethal allele, directional selection
w
Survivors
Relative genotype frequencies
f(b) after reproduction
w = 0
survivors = 0
relative genotype frequencies = 0
f(b) after reproduction NOT 0
Selection favouring heterozygosity
mutants for hetero vs homos
____________ effect
When heterozygous genotype is favoured, a balanced
polymorphism effect occurs
- Alleles reach stable equilibrium frequencies that are maintained in a steady state
- Selective pressures maintain mutant allele in heterozygotes, but act against it in homozygotes
Equilibrium allele frequency calculations
remember PEST
pE = allele freq of C
qE = allele freq of c
s = difference in fitness advantages of CC vs Cc
t = difference in fitness advantages of cc vs Cc
pE = t / (s+t)
qE = s / (s+t)
Mutation (diversity)
purpose of mutation
the ultimate source of all new genetic variation in populations
