BIOB51 LECTURE 11-12: PATTERNS OF SELECTION EXAM
QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS LATEST UPDATE
broad categories of selection and the patterns of selection falling under each (2)
1. patterns that maintain genetic diversity
- negative frequency-dependence
- heterozygote advantage, heterozygote overdominance
- heterozygote inferiority, heterozygote underdominance
2. patterns that reduce genetic diversity
- directional selection, one allele favoured
- heterozygote inferiority, heterozygote underdominance
Can populations under any types of the above patterns of selection be at Hardy-
Weinberg?
no; because these are all types of natural selection
DEF negative frequency-dependence
fitness of genotype depends on frequency in the population where allele frequencies
fluctuate around a STABLE equilibrium level b/c as the proportion of an allele increases,
selection for it decreases (AKA rare phenotype advantage)
, In negative frequency-dependence pattern of selection, what happens when the
frequencies of one allele is greater than that of the other?
the next generation will have more frequencies of the other allele
In negative frequency-dependent pattern of selection, what happens with the
frequencies of both alleles are the same?
the next generation will also have the same frequency of alleles b/c both alleles are
equally fit
DEF heterozygote advantage or heterozygote overdominance
fitness is highest in heterozygotes, often observed when the allele frequency is often at
stable equilibrium (because selection of both those alleles is occurring in the
heterozygous state) and heterozygotes are at a higher frequency than expected under
H-W, leading to BALANCED POLYMORPHISM
What is balanced polymorphism and what type of selection favours it?
stable equilibrium with more than one allele; favoured by heterozygote advantage
pattern of selection
DEF direction selection or one allele favoured
often leads to fixation of favoured allele and loss of the other allele
What does the rate of change depend on for directional selection? (2)
1. initial frequency of each allele
2. type of dominance
What type of dominance would increase the rate of change for directional
selection?
QUESTIONS AND ANSWERS WITH COMPLETE
SOLUTIONS LATEST UPDATE
broad categories of selection and the patterns of selection falling under each (2)
1. patterns that maintain genetic diversity
- negative frequency-dependence
- heterozygote advantage, heterozygote overdominance
- heterozygote inferiority, heterozygote underdominance
2. patterns that reduce genetic diversity
- directional selection, one allele favoured
- heterozygote inferiority, heterozygote underdominance
Can populations under any types of the above patterns of selection be at Hardy-
Weinberg?
no; because these are all types of natural selection
DEF negative frequency-dependence
fitness of genotype depends on frequency in the population where allele frequencies
fluctuate around a STABLE equilibrium level b/c as the proportion of an allele increases,
selection for it decreases (AKA rare phenotype advantage)
, In negative frequency-dependence pattern of selection, what happens when the
frequencies of one allele is greater than that of the other?
the next generation will have more frequencies of the other allele
In negative frequency-dependent pattern of selection, what happens with the
frequencies of both alleles are the same?
the next generation will also have the same frequency of alleles b/c both alleles are
equally fit
DEF heterozygote advantage or heterozygote overdominance
fitness is highest in heterozygotes, often observed when the allele frequency is often at
stable equilibrium (because selection of both those alleles is occurring in the
heterozygous state) and heterozygotes are at a higher frequency than expected under
H-W, leading to BALANCED POLYMORPHISM
What is balanced polymorphism and what type of selection favours it?
stable equilibrium with more than one allele; favoured by heterozygote advantage
pattern of selection
DEF direction selection or one allele favoured
often leads to fixation of favoured allele and loss of the other allele
What does the rate of change depend on for directional selection? (2)
1. initial frequency of each allele
2. type of dominance
What type of dominance would increase the rate of change for directional
selection?
