Chapter 18: Population and Evolutionary Genetics Flashcards
Define mendelian population
A group of interbreeding, sexually reproducing individuals that have a common set of genes
Define gene pool
A common set of genes withing a group
Define genotype frequency
the number of individuals with a given genotype divided by the total number of individuals
Define allelic frequencies
The gene pool of a population
Define Hardy-Weinberg Law
A mathematical model that evaluates the effect of reproduction on the genotypic and allelic frequencies of a population
What are the six factors in population genetics?
- Mating patterns
- Migration
- Mutation
- Recombination
- Natural selection
- Random fluctuation
What are the 5 assumptions of Hardy-Weinberg?
- Mating is random
- Population is large
- There is no selection
- No mutation
- No migration
Define genetic drift
Changes in allele frequency due to random factors
Does genetic drift affect large populations or small population more?
Small
Natural selection has three categories regarding genetics; what are they?
- Directional selection
- Overdominance
- Underdominance
Define directional selection
One allele has higher fitness than the other
Define overdominance
Heterozygotes have higher fitness than either homozygotes
Define under dominance
Heterozygotes have lower fitness than either homozygote
What is the difference between relative fitness vs. absolute fitness?
Relative: relative to other genotypes
Absolute: measures contribution to next generation
Which type of fitness is most commonly measured?
Relative fitness
How do mutations allow scientists to predict evolutionary patterns?
Mutation occurs at a consistent rate, changes in DNA can be observed to allow dating of changes and how long ago they occurred
How do you calculate the frequency of an allele?
Frequency of an allele = (number of copies of the allele) / (number of copies of all alleles at the locus)
If the requirements of the Hardy-Weinberg law are met, what are the two predictions?
- The allelic frequencies of a population do not change
AND
- The genotypic frequencies stabilize (will not change) after one generation in the proportions p^2 (the frequency of AA), 2pq (the frequency of Aa), and q^2 (the frequency of aa), where p equals the frequency of “A” and q equals the frequency of allele “a”.
Define Hardy-Weinberg equilibrium
When genotypes are in the expected proportions of p^2, 2pq, and q^2
(1) Which of the following statements is NOT an assumption of the Hardy-Weinberg law?
a. The allelic frequencies (p and q) are equal
b. The population is randomly mating
c. The population is large
d. Natural selection has no effect
(2) In cats, all-white color is dominant over colors other than all-white. In a population of 100 cats, 19 are all-white. Assuming that the population is in Hardy-Weinberg equilibrium, what is the frequency of the all-white allele in this population?
Define inbreeding
A form of non-random mating when organisms have a preferential mating between related individuals.
Define inbreeding depression
An increase appearance of lethal and deleterious traits caused from inbreeding
Nonrandom mating alters the frequencies of _____ but not the frequencies of _____
a. alleles, phenotypes
b. genotypes, alleles
c. phenotypes, genotypes
d. alleles, genotypes
b. genotypes, alleles
Nonrandom mating alters the frequencies of genotypes but not the frequencies of alleles
Define equilibrium
A point at which there is no change in the allelic frequencies of a population
Recurrent _____ cause(s) changes in the frequencies of alleles.
a. inbreeding
b. competition
c. mutations
d. cell division
c. mutations
Recurrent mutations cause changes in the frequencies of alleles.
At equilibrium, how are allelic frequencies determined?
By forward and reverse mutation rates.
Ex: If mutation rates are low, the effect of mutation on allelic frequencies per generation is very small
Define migration / gene flow
An influx of genes from other populations
Migration has two major effects. What are they?
- Causes the gene pools of different populations to become more similar
- Adds genetic variation to populations
(3) In each generation, 10 random individuals migrate from population A to population B. What will happen to allelic frequency q as a result of migration when q is equal in populations A and B?
a. q in A will decrease
b. q in B will increase
c. q will not change in either A or B
d. q in B will become q^2
Define sampling error
A deviation from an expected ratio due to limited sample size
Define effective population size (Ne)
When population size is the equivalent number of breeding adults
(4) Which of the following statements describes an example of genetic drift?
a. Allele g for fat production increases in a small population because birds with more body fat have higher survivorship in a harsh winter
b. Random mutation increases the frequency of allele A in one population but not in another
c. Allele R reaches a frequency of 1.0 because individuals with genotype rr are sterile
d. Allele m is lost when a virus kills all but a few birds in a population and, just by chance, none of the surviving birds possess allele m
Define founder effect
A way that sampling errors can arise from the establishment of a population by a small number of individuals
Define genetic bottleneck
A way in which genetic drift arises is when a population undergoes a drastic reduction in size
Define fixation
When an allele has reached a frequency of 1
Explanation:
Through random change, an allele may eventually reach a frequency of either 1 or 0, at which point all individuals in the population are homozygous for one allele. 0 means an allele becomes lost in a population, and 1 means the allele is “fixed” in the population
When an allele reaches a frequency of 0 in a population, it is impossible to get that allele back.
a. True
b. False
b. False
The allele can return to the population through migration of another population or by mutation
What are the 3 causes of genetic drift?
- Continuous small population size
- Founder effect
- Genetic bottleneck
Define fitness
The relative reproductive success of a genotype
Define selection coefficient (s)
The relative intensity of selection against a genotype
How is natural selection measured?
Natural selection is measured as fitness
(5) The average numbers of offspring produced by three genotypes are GG = 6, Gg = 3, and gg = 2. What is the fitness of Gg?
a. 3
b. 0.5
c. 0.3
d. 0.27
Define evolution
In the biological sense, refers only to genetic change taking place in a group of organisms
Define anagenesis
Evolution taking place in a single lineage (a group of organisms connect by ancestry) over time
Define cladogenesis
The splitting of one lineage into 2 and the two branches no longer have a common gene pool and evolve independently of one another
Define species
Different kinds or types of living organisms
Define the biological species concept.
The method used to separate organisms into independently evolving units
Define the reproductive isolating mechanism.
Any biological factor or mechanism that prevents gene exchange
Define prezygotic reproductive isolating mechanisms.
The prevention of gametes from two different species fusing together and forming a hybrid zygote
Define postzygotic reproductive isolating mechanisms.
The gametes of two species may fuse and form a zygote, but there is no gene flow between the two species, either because other resulting hybrids are inviable or sterile or because reproduction breaks down in subsequent generations
