UBC BIOL 121 Practice Questions and
Correct Answers
Gene pool ✅all of the alleles of all the genes in a certain population
Hardy-weinberg principle ✅genotype frequencies in a large population do not change
from generation to generation in the absence of evolutionary processes
Claims of hardy-weinberg principle ✅(1) if the frequencies of alleles a1 and a2 in a
population are given by p and q, then the frequencies of genotypes a1a1, a1a2, a2a2
will be given by p^2, 2pq, and q^2 for generation after generation.
(2) when alleles are transmitted via meiosis and random combination of gametes, their
frequencies don't change over time.
Assumptions of hardy-weinberg principle ✅no natural selection at gene in question
No genetic drift, or random allele frequency changes, affecting the gene in question
No gene flow
No mutation
Random mating with respect to the gene in question
Genetic variation ✅number and relative frequency of alleles present in a particular
population; the proportion of phenotypic variation in a trait that is due to genetic rather
than environmental influences
Directional selection ✅favours one extreme phenotype with the result that the average
phenotype of a population changes in one direction; generally reduces overall genetic
variation; if continues over time will result in the loss and fixation of alleles
Purifying selection ✅when disadvantageous alleles decline in frequency
Stabilizing selection ✅favours phenotypes near middle of range of phenotypic
variation; reduces genetic variation; no change in average value of the trait over time
Disruptive selection ✅eliminates phenotypes near the average value and favours
extreme phenotypes; genetic variation is maintained
Balancing selection ✅no single allele is favoured, balance among alleles in terms of
fitness and frequency
Frequency-dependent selection ✅certain alleles are favoured when they are rare, not
when common
, Heterozygote advantage ✅heterozygote individuals have higher fitness than
homozygote individuals
Genetic drift ✅any change in allele frequencies due to chance
Random with respect to fitness
Most pronounced in small populations
Over time, can lead to random loss or fixation of alleles
Founder effect ✅change in allele frequencies that occurs when a new population is
established
Genetic bottleneck ✅sudden reduction in number of alleles in a population; drift occurs
during and causes change in allele frequenices
Gene flow ✅movement of alleles from one population to another
Random with respect to fitness
Increases similarity of allele frequencies in source and recipient population, making
them more alike
Mutation ✅dna polymerase makes an error as it copies a dna molecule -> change in
sequence
Increases genetic diversity
Random with respect to fitness
Slow compared w/ selection, genetic drift, and gene flow as an evoluationary
mechanism
Introduces new alleles into every individual in every population
Deleterious mutation ✅alleles that lower fitness
Beneficial mutation ✅alleles that higher fitness
Inbreeding ✅increases homozygosity
Doesn't cause evolution, can speed rate of evolutionary change
Changes genotype frequencies not allele frequencies
Increases rate at which purifying selection eliminates recessive deleterious alleles from
a population
Mating between relatives
Inbreeding depression ✅decline in average fitness
Results from many recessive alleles represent loss of function mutations or many genes
are under intense selection for heterozygote advantage
Assortive mating ✅mating is nonrandom with respect to specific traits
Correct Answers
Gene pool ✅all of the alleles of all the genes in a certain population
Hardy-weinberg principle ✅genotype frequencies in a large population do not change
from generation to generation in the absence of evolutionary processes
Claims of hardy-weinberg principle ✅(1) if the frequencies of alleles a1 and a2 in a
population are given by p and q, then the frequencies of genotypes a1a1, a1a2, a2a2
will be given by p^2, 2pq, and q^2 for generation after generation.
(2) when alleles are transmitted via meiosis and random combination of gametes, their
frequencies don't change over time.
Assumptions of hardy-weinberg principle ✅no natural selection at gene in question
No genetic drift, or random allele frequency changes, affecting the gene in question
No gene flow
No mutation
Random mating with respect to the gene in question
Genetic variation ✅number and relative frequency of alleles present in a particular
population; the proportion of phenotypic variation in a trait that is due to genetic rather
than environmental influences
Directional selection ✅favours one extreme phenotype with the result that the average
phenotype of a population changes in one direction; generally reduces overall genetic
variation; if continues over time will result in the loss and fixation of alleles
Purifying selection ✅when disadvantageous alleles decline in frequency
Stabilizing selection ✅favours phenotypes near middle of range of phenotypic
variation; reduces genetic variation; no change in average value of the trait over time
Disruptive selection ✅eliminates phenotypes near the average value and favours
extreme phenotypes; genetic variation is maintained
Balancing selection ✅no single allele is favoured, balance among alleles in terms of
fitness and frequency
Frequency-dependent selection ✅certain alleles are favoured when they are rare, not
when common
, Heterozygote advantage ✅heterozygote individuals have higher fitness than
homozygote individuals
Genetic drift ✅any change in allele frequencies due to chance
Random with respect to fitness
Most pronounced in small populations
Over time, can lead to random loss or fixation of alleles
Founder effect ✅change in allele frequencies that occurs when a new population is
established
Genetic bottleneck ✅sudden reduction in number of alleles in a population; drift occurs
during and causes change in allele frequenices
Gene flow ✅movement of alleles from one population to another
Random with respect to fitness
Increases similarity of allele frequencies in source and recipient population, making
them more alike
Mutation ✅dna polymerase makes an error as it copies a dna molecule -> change in
sequence
Increases genetic diversity
Random with respect to fitness
Slow compared w/ selection, genetic drift, and gene flow as an evoluationary
mechanism
Introduces new alleles into every individual in every population
Deleterious mutation ✅alleles that lower fitness
Beneficial mutation ✅alleles that higher fitness
Inbreeding ✅increases homozygosity
Doesn't cause evolution, can speed rate of evolutionary change
Changes genotype frequencies not allele frequencies
Increases rate at which purifying selection eliminates recessive deleterious alleles from
a population
Mating between relatives
Inbreeding depression ✅decline in average fitness
Results from many recessive alleles represent loss of function mutations or many genes
are under intense selection for heterozygote advantage
Assortive mating ✅mating is nonrandom with respect to specific traits
