Population Genetics: Hardy-Weinberg, Selection, and Evolutionary Models

What is the Hardy-Weinberg equilibrium?

A principle that describes the genetic variation in a population that is not evolving, characterized by specific allele frequencies.

What does it mean if a population is in Hardy-Weinberg equilibrium?

It means that allele frequencies remain constant from generation to generation in the absence of evolutionary influences.

What are the conditions necessary for Hardy-Weinberg equilibrium?

1) Large population size, 2) No mutations, 3) No gene flow, 4) Random mating, 5) No natural selection.

What is relative fitness?

A measure of the reproductive success of an individual relative to the average reproductive success in the population.

What is genetic drift?

A mechanism of evolution that involves random changes in allele frequencies, particularly significant in small populations.

How does non-random mating affect evolution?

It can change genotype frequencies without altering allele frequencies, potentially leading to inbreeding depression.

What is inbreeding depression?

Reduced biological fitness in a population due to inbreeding, which increases the chance of deleterious alleles being expressed.

What is directional selection?

A type of natural selection that favors one extreme phenotype over others, leading to a shift in allele frequencies.

What is stabilizing selection?

A type of natural selection that favors intermediate phenotypes, reducing variation in a trait.

What is disruptive selection?

A type of natural selection that favors extreme phenotypes over intermediate ones, potentially leading to speciation.

What is the founder effect?

A phenomenon that occurs when a small group of individuals establishes a new population, leading to reduced genetic variation.

What is gene flow?

The transfer of genetic material between populations, which can increase genetic diversity and counteract the effects of genetic drift.

What is sexual selection?

A mode of natural selection where individuals with certain traits are more likely to attract mates and reproduce.

What is sperm competition?

A form of sexual selection where male reproductive success is determined by the competition between sperm from different males.

What is frequency-dependent selection?

A type of selection where the fitness of a phenotype depends on its frequency relative to other phenotypes in a population.

What is environment-dependent selection?

Selection that varies based on environmental conditions, affecting which traits are favored in a population.

What is heritability?

The proportion of variation in a trait that can be attributed to genetic differences among individuals in a population.

Why are most human diseases caused by recessive alleles?

Recessive alleles can be carried by individuals without expressing the disease, allowing them to persist in the population.

What is a genetic bottleneck?

A sharp reduction in the size of a population due to environmental events, leading to a loss of genetic diversity.

What is a deleterious mutation?

A mutation that is harmful to the organism, potentially reducing its fitness.

What is polygamy?

A mating system in which an individual has multiple mating partners.

What is polygyny?

A form of polygamy where one male mates with multiple females.

What is polyandry?

A form of polygamy where one female mates with multiple males.

What is a phenotype?

The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.

What is the primary focus of population genetics theory?

To model how allele frequencies change in response to natural selection.

What does the theory of population genetics predict about allele frequency changes?

It should accurately predict changes under various selection schemes.

What is the fitness of individuals with the 1/1 genotype in Dawson's flour beetle study?

Zero fitness, as they do not survive.

What happens to the frequencies of the + and 1 alleles over generations in Dawson's study?

The frequency of the 1 allele decreases while the frequency of the + allele increases.

What is the expected outcome for the + allele after one generation in Dawson's experiment?

The frequency of the + allele increases due to the survival of non-lethal genotypes.

What is the method used by Dawson to predict evolutionary changes in his populations?

Quantitative predictions based on allele frequency calculations.

What is the role of simplifying assumptions in population genetics models?

They help in predicting outcomes but may not fully reflect real-world complexities.

What does the term 'eugenics' refer to in the context of Buck v. Bell?

A movement aimed at improving the genetic quality of the human population.

What is the impact of HIV infection on the fitness of heterozygotes?

Heterozygotes may progress more slowly to AIDS, potentially increasing their fitness.

What does the term 'recessive lethal allele' mean?

An allele that results in death when present in homozygous form.

What is the purpose of using empirical data in population genetics theory?

To compare predictions with actual observed changes in allele frequencies.

What is the expected result of selection favoring heterozygotes?

An increase in the frequency of the heterozygote genotype in the population.

What is the significance of the term 'fitness' in evolutionary biology?

Fitness refers to an individual's ability to survive and reproduce in a given environment.

What is the relationship between allele frequency and natural selection?

Natural selection can lead to changes in allele frequencies over generations.

How does the concept of gene pool relate to allele frequency?

The gene pool contains all alleles in a population, and allele frequency is the proportion of each allele.

What does the term 'homozygous' mean?

Having two identical alleles for a particular gene.

What does the term 'heterozygous' mean?

Having two different alleles for a particular gene.

What is the outcome of the selection on dominant alleles compared to recessive alleles?

Dominant alleles may be more visible to selection than recessive alleles.

What is the frequency of the + allele in the new gene pool?

0.67

What is the frequency of the 1 allele in the new gene pool?

0.33

How many zygotes are created from generation one's gene pool?

100 zygotes

What is a limitation of using pencil-and-paper calculations in predicting evolution?

It is tedious to track alleles through multiple generations.

What tools can be used to predict population evolution more efficiently?

Spreadsheet applications or population genetics programs.

What happens to the rate of evolution as the recessive allele becomes rare?

The rate of evolution slows dramatically.

What is the selection coefficient (s) in the context of recessive alleles?

It represents the strength of selection against homozygous recessives.

What is the equation for predicting the frequency of allele a in the next generation?

q' = q(1 - sq) / (1 - sq²)

What happens to a lethal dominant allele in a population?

It is eliminated from the population in a single generation.

What is the relationship between selection on recessive and dominant alleles?

Selection against a recessive allele favors the dominant allele and vice versa.

What does the model of evolution predict about the changes over 12 generations?

It predicts significant changes in allele frequencies.

What is the mean fitness of a population as the dominant allele frequency increases?

The mean fitness of the population rises.

What is the effect of heterozygous individuals on the selection of recessive alleles?

Heterozygous individuals hide recessive alleles from selection.

What is the significance of Dawson's experiment in population genetics?

It demonstrates that predictions made with population genetics models are accurate.

What is the outcome when the frequency of allele a is 0.01?

In the next generation, its frequency will be approximately 0.0099.

What does the adaptive landscape show in relation to allele frequencies?

It shows changes in population mean fitness as a function of allele frequencies.

What does the equation p' = p(1 - s) / (2sp + sp²) predict?

It predicts the frequency of the dominant allele A in the next generation.

What happens to the frequency of a lethal recessive allele over generations?

It declines slowly as it becomes rare.

What is the significance of the term 'fixation' in population genetics?

Fixation refers to the point where an allele's frequency reaches 100% in the population.

What does the term 'mean fitness' refer to in the context of evolution?

It refers to the average reproductive success of individuals in a population.

How does selection against a dominant allele affect the population?

It favors the survival of homozygous recessives.

What does the term 'adaptive landscape' illustrate?

It illustrates the relationship between fitness and allele frequencies in a population.

What happens to mean fitness as a dominant allele becomes common?

Mean fitness of the population rises.

What are adaptive landscapes?

Graphs of mean fitness as a function of allele frequency.

What occurs when a recessive allele becomes common?

The rate of evolution increases dramatically.

What is the outcome when a recessive allele reaches a frequency of 100%?

The recessive allele becomes fixed in the population.

How does the frequency of a recessive allele affect the rate of evolution?

When common, evolution is rapid; when rare, it is slow.

What does the Hardy-Weinberg equilibrium principle explain?

It explains the relationship between allele frequencies and genotype frequencies in a population.

What is the genotype frequency of AA when the recessive allele frequency is 0.95?

0.0025.

What happens to allele frequencies when a recessive allele is rare?

There will be little change in allele frequencies in the next generation.

What is heterozygote superiority?

A condition where heterozygotes have higher fitness than either homozygote.

What did Mukai and Burdick's experiment on fruit flies demonstrate?

The frequency of the viable allele increased rapidly but then slowed, reaching an equilibrium.

What is the equilibrium frequency of the viable allele in Mukai and Burdick's experiment?

About 0.79.

What is the equilibrium frequency of the lethal allele in Mukai and Burdick's experiment?

About 0.21.

Why might a lethal allele be maintained at a high frequency in a population?

Due to heterozygote superiority balancing its disadvantages.

What is the significance of the relationship between genotype and phenotype?

Dominant and recessive describe this relationship, not necessarily fitness.

What percentage of human disease-causing alleles are autosomal dominants?

About 30%.

What is the effect of selection on heterozygotes and homozygotes?

Selection can favor or disfavor both types of variants.

What happens to the fitness of phenotypes when a recessive allele is rare?

Most copies are hidden in heterozygotes and are immune from selection.

What does the term 'natural selection' refer to?

The process by which certain traits increase in frequency due to their advantage in survival and reproduction.

What is the main conclusion from Dawson's experiment regarding allele frequency?

Dominance and allele frequency interact to determine the rate of evolution.

What is the significance of allele frequency in evolutionary biology?

It influences the rate of evolution and the dynamics of natural selection.

What does the model's fit indicate about the initial data analysis?

The model's fit does not represent a rigorous test because the data was examined first, and then the model was adjusted to fit the data.

What happens to allele frequencies under heterozygote superiority?

Genetic diversity can be maintained indefinitely.

What is the outcome when heterozygotes have inferior fitness?

The population may evolve toward fixation or loss of alleles.

What does the equation Ap = 0 indicate?

Equilibrium occurs when the frequency of allele A₁ is either 0 or q = 0.

What is the equilibrium frequency of allele A₁ when s = 0.4 and t = 0.6?

0.6.

What does the red curve in Figure 6.22a indicate about allele A₁?

It indicates that the equilibrium is stable; the population will return to equilibrium if perturbed.

What happens to mean fitness as allele frequency approaches its stable equilibrium?

Mean fitness rises to a maximum.

What does the blue curve in Figure 6.22a indicate about allele A₁?

It describes a locus with heterozygote inferiority, leading to unstable equilibrium.

What is the relationship between allele frequency and mean fitness in a locus with heterozygote inferiority?

Mean fitness is lowest at the unstable equilibrium, and rises as allele frequency moves away from it.

What are compound chromosomes?

Homologous chromosomes that have swapped entire arms.

What types of gametes are produced by flies with compound chromosomes?

Gametes with both homologous chromosomes, one member of the pair, the other member, or neither.

What fraction of zygotes from mating compound chromosome flies are viable?

One-quarter of the zygotes are viable.

What is the consequence of having too many or too few copies of chromosome arms in zygotes?

They are inviable.

What does the term 'overdominance' refer to in genetics?

A situation where heterozygotes have higher fitness than either homozygote.

What is 'underdominance' in the context of allele fitness?

A situation where heterozygotes have lower fitness than either homozygote.

How does the model predict allele fixation under heterozygote inferiority?

The favored allele will reach a frequency of 100%, while the disfavored allele will disappear.