Lecture 10: Population Genetics

Question 1

population genetics

Answer 1

the study of the genetics of a population and how the alleles vary with time

Question 2

population

Answer 2

an interbreeding group of the same species within a given geographical area

Question 3

gene pool

Answer 3

the collection of all alleles in the members of the population

Question 4

gene flow

Answer 4

alleles can move between populations when individuals migrate and mate

Question 5

give an example of how phenotype frequencies vary in different populations

Answer 5

phenylketonuria (PKU), a heritable metabolic disorder, autosomal recessive trait

Question 6

what does the Hardy-Weinberg Law clarify?

Answer 6

the relation between genotype and allele frequency within a generation and from one generation to the next

Question 7

five assumptions that must be met for a population to be at hardy-weinberg equilibrium

Answer 7

• infinitely large population
• individuals mate at random
• no new mutations appear in gene pool
• no migration into or out of population
• no genotype-dependent differences in ability to survive and reproduce

Question 8

does any population follow all assumptions of Hardy-Weinberg law?

Answer 8

no; all populations violate one or more assumptions of Hardy-Weinberg law

Question 9

why can HW law be used despite its limitations? 1

Answer 9

• equations derived based on assumptions are remarkably robust
• HW law can be used as a null model

Question 10

p =

Answer 10

allele frequency of one allele

Question 11

q =

Answer 11

allele frequency of a second allele

Question 12

p + q =

Answer 12

1
all of the allele frequencies together equals 1 or the whole collection of alleles

Question 13

HW law

Answer 13

p^2 + 2pq + q^2 = 1
all of the genotype frequencies together equals 1
p^2 and q^2 = genotype frequencies for each homozygote
2pq = genotype frequency for heterozygotes

Question 14

allelic frequency=

Answer 14

of particular allele/total # of alleles in the population
- count both chromosomes of each individual
- allele frequencies affect the genotype frequencies

Question 15

how does HW law relate from generation to generation?

Answer 15

• allele frequencies do not change from generation to generation in a population at HW equilibrium
• a HW population achieves the genotype frequencies of p2, 2pq, q2 in just one generation and once at equilibrium maintains them in subsequent generations
• only 1 generation is required to reach HW equilibrium

Question 16

why do all natural populations violate one or more assumptions of the HW law?

Answer 16

• natural populations are undergoing microevolution: genetic change due to changing allelic frequencies in populations
• allelic frequencies can change with: nonrandom mating, gene flow, genetic drift, natural selection (unequal reproductive success)

Question 17

impact of genetic drift on evolutionary equilibrium

Answer 17

• chance random fluctuations in allele frequency that have a neutral effect on fitness
• random allele frequency fluctuations might make certain disease alleles more common in particular populations

Question 18

are smaller or larger populations more affected by genetic drift?

Answer 18

smaller populations are more affected than larger populations

Question 19

sampling biases are —- pronounced in small populations

Answer 19

more

Question 20

impact of natural selection

Answer 20

acts on differences in fitness to alter allele frequencies

Question 21

fitness

Answer 21

individual’s relative ability to survive and transmit genes to the next generation (viability and reproductive success)

Question 22

natural selection

Answer 22

individuals with higher fitness strive and reproductive more than individuals with lower fitness

Question 23

why might there be a decrease in the frequency of a recessive allele over time?

Answer 23

• homozygous recessive genotype (rr) has decreased fitness
• fitness of RR and Rr is the same

Question 24

why is selection unable to reduce the frequency of recessive lethal alleles to zero?

Answer 24

• when q is small, the frequency of homozygous recessive individuals is low
• most copies of the q allele are in heterozygotes, who do not have reduced fitness

Question 25

heterozygote advantage

Answer 25

although allele frequency of lethal alleles should continue to decline, some stay in population at stable frequencies

Question 26

heterozygote advantage conferred by the sickle-cell allele

Answer 26

- In heterozygotes, the presence of some sickled red blood cells interferes with the life cycle of the malaria parasite. - As a result, HbA/HbS individuals are more resistant to severe malaria compared to HbA/HbA individuals.

Question 27

how does the time of onset of a recessive, negative-impact trait influence frequency?

Answer 27

- if onset is in middle or late age, after reproduction, then the trait will not affect fitness - sustain little or no negative selection

Question 28

define evolutionary equilibrium:

Answer 28

a balance between mutation to a new allele and selection against the allele

Question 29

what is the ultimate source of new variation?

Answer 29

mutations: - when new allele has effect on fitness, selection will drive frequency towards an equilibrium with wild-type allele - if new allele has no effect on fitness, genetic drift will determine its frequency

Question 30

define a haplotype

Answer 30

short for haploid genotype - a group of alleles or DNA variations that are inherited together from a single parent because they are located close to each other on the same chromosome.

Question 31

what is a possible application of Hardy-Weinberg equilibrium?

Answer 31

1. DNA collected from evidence at crime scene 2. DNA collected from suspected 3. five specific DNA sequences from different chromosomes are labeled and separated by size - blood (victim), blood (suspect), skin (evidence), blood (evidence) 4. use HW to calculate the probability that another person in the suspect's population group has the same pattern of these alleles

Question 32

what is the purpose of haplotype analysis?

Answer 32

enables the correlation of occurrence of trait with occurrence of a particular allele

Question 33

use of SNP analysis

Answer 33

genotype many individuals and correlate with phenotype