Lesson 11 Population Genetics Flashcards
Gene pool
Total of all genes within a particular population
Population
A group of individuals of the same species that are capable of interbreeding with one another. Dynamic units that change size, location and genetic composition.
polymorphism
Many traits display variation within a population, either phenotypically or genetically.
polymorphic gene
Exists as two or more alleles in a population
monomorphic gene
Exists predominantly as a single allele in a population. Found in 99 percent or more cases.
allele frequency
No. Of copies of allele in population/
Total no. Of all alleles for that gene in population
Relative percentage of an allele of a given green
Genotype frequency
No. Of individuals with a particular genotype in a population/
Total number of individuals in a population
Relative percentage of a given genotype
Use of hardy-Weinberg equation
Used to calculate genotype frequencies based on allele frequencies
Hardy Weinberg equation
p^2 + 2pq + q^2 = 1
p^2 = genotype frequency of AA
2pq = genotype frequency of Aa
q^2 = genotype frequency of aa
What conditions must be met for Hardy Weinberg equation to work?
Large population, random mating, no migration, no natural selection, and no mutations
assortative mating
When two individuals are more likely to mate due to similar phenotypic characteristics
disassortative mating
When unlike phenotypes mate
inbreeding
When two genetically related individuals mate with each other
outbreeding
Mating between unrelated individuals
coefficient of inbreeding (F)
F = Sum (1/2)^n (1 + Fa) n = number of individuals in the inbreeding path Fa = inbreeding coefficient of the common ancestor
Inbreeding: common ancestor
Someone who is an ancestor to both fo an individual’s parents
Size of inbreeding path
The shortest no. Of steps through the pedigree that includes both parents and the common ancestor. Calculated by adding together all of the individuals in the path except for the individual of interest.
Measuring effects of inbreeding at population level
Frequency of AA= p^2 + Fpq
Frequency of Aa = 2pq (1-F)
Frequency of aa = q^2 + Fpq
What is effect of inbreeding
Lower the relative number of heterozygotes
Two types of evolutionary forces
- Neutral forces
2. Adaptive forces
Neutral forces
Alter allele frequencies in a random manner. Without regard to survival of the individual.
Adaptive forces
“select” for the survival of individuals who possess alleles that make them well adapted to their environment
What do new mutations provide a population?
Genetic variability
Mutation rate
Likelihood that a gene will be altered by a new mutation; expressed as the number of new mutations Ina given gene per generation
10^5 to 10^6 per generation
Random genetic drift
Random changes in allele frequencies due to sampling error
What does rate at which allele becomes fixed depend on?
Population size
Probability of fixation
1/2N (assuming an equal no. Of males and females contributing to the next generation)
Probability of elimination
1 - 1/2N
time it will take for fixation to occur
Mean t = 4N
Mean t = average no. Of generations to achieve fixation. N equals the no. Of individuals in a population.
How is random genetic drift directional?
It leads to allele fixation or elimination
When are allele frequencies altered?
When migration occurs between two populations
conglomerate
Population after migration has occurred
change in allele frequency in conglomerate population
deltaPc = m(Pd - PR)
DeltaPc is change in allele frequency
Pd is allele frequency in donor population
PR is allele frequency in original recipient population
m = no. Of donor individuals in cong. population/
Total no. Of individuals in cong. population
Natural selection
Conditions found in nature select for the survival of individuals who have characteristics that make them well adapted to their environment t
Darwinian fitness (W)
Relative likelihood that a phenotype will survive and contribute to the gene pool of the next generation compared to another phenotype
Selection coefficient
Measure of the degree to which a genotype is selected against
s = 1 - W
What does process of natural selection result in
An increase in the mean fitness of the population
Balanced polymorphism
A polymorphism that exists because an equilibrium has been achieved between the genotype and the environment
Why might balanced polymorphism occur?
Heterozygote selective advantage or a species may occupy a region that contains heterogeneous environments
How is higher fitness of heterozygote balanced in balanced polymorphism?
Allele frequency of A = Saa / SAA + Saa
Allele frequency of a = SAA/SAA + Saa
Experiment 25A: natural selection in moths
hypothesis
The coloration of b. betularia affects the probability that birds will see and eat them. This natural selection leads to the survival of those moths with coloration more closely matching that on which they rest, whether that be in polluted or unpolluted woods.
Experiment 25A: natural selection in moths
Starting materials
Samples of b. betularia, broth carbonaria and ty0pical, were collected from the wild. In some cases, they were bred in a lab, to be released later into the wild.
Experiment 25A: natural selection in moths
protocol
- mark the underside of carbonaria and typical moths with cellulose paint
- Release equal numbers of marked carbonaria and typical moths in either polluted woods near an industrial area of Birmingham or in an unpolluted woods in Dorset, England
- On several consecutive days, recapture moths that have been marked. This can be done by attract ting them to a mercury vapor light. Record the number of recaptured moths.
- Also, sit in a blind and observe the moths on a tree trunk. Record the numbers and types of sitting moths that are eaten by birds.
Experiment 25A: natural selection in moths
Interpreting the data
carbonaria were more likely to be eaten in unpolluted woods by birds.
Typical were more likely to be eaten in polluted woods
Birds act as selective agents and the the melanic forms of betularia are Ata. Cryptic advantage in an industrial area.
