Chapter 20 Genes With Populations

The bottleneck effect refers to a situation where a population undergoes a significant reduction in size due to a catastrophic event or intense selection pressure. This reduction in population size leads to a decrease in genetic variability as certain alleles are lost from the gene pool. The founder effect, on the other hand, occurs when a small group of individuals establish a new population, leading to a loss of genetic diversity. The Hardy-Weinberg effect refers to the equilibrium of allele frequencies in a population under certain conditions. Polymorphism refers to the presence of multiple forms of a gene in a population. The adaptive effect is not a recognized term in genetics.

Darwin proposed natural selection as a mechanism of evolution that acts on variants within populations and leads to the evolution of different species. This theory suggests that individuals with advantageous traits are more likely to survive and reproduce, passing on their traits to future generations. Over time, these advantageous traits become more common in the population, leading to the formation of new species. Mendel is known for his work on genetics, Lyell for his contributions to geology, and Malthus for his ideas on population growth, but it was Darwin who proposed the concept of natural selection.

The total of all the alleles of all the genes in a population is referred to as a gene pool. This term represents the collection of genetic information and variations within a population. It encompasses all the different alleles that individuals possess for each gene, providing a diverse range of genetic material from which future generations can inherit. The concept of a gene pool is crucial in understanding how genetic traits are passed on and how populations evolve over time.

The term in the algebraic form of the Hardy-Weinberg equilibrium for the heterozygote genotype frequency is 2pq. This is because in a population with two alternative alleles, p and q, the frequency of the heterozygote genotype (Aa) is determined by multiplying the frequency of one allele (p) by the frequency of the other allele (q), and then multiplying the result by 2. This equation accounts for the probability of randomly selecting two different alleles from the gene pool.

The gene pool refers to all of the alleles of genes within a population. Alleles are different versions of a gene that can determine different traits or characteristics. The gene pool represents the total genetic diversity present in a population, including all the different alleles that individuals possess. This diversity is important for the survival and adaptation of a population to changing environments. Therefore, the correct answer is "all of the alleles of genes within a population."

Natural selection is the correct answer because it refers to the process by which certain traits or characteristics that increase the chances of survival and reproduction become more common in a population over time. This process leads to the genetic preservation of these advantageous features, as individuals with these traits are more likely to pass them on to future generations.

The Hardy-Weinberg equations are mathematical formulas that describe the genetic equilibrium in a population. These equations only hold true when certain assumptions are met, such as a large population size, random mating, no mutation, no migration, and no natural selection. Therefore, the correct answer is that a population is only in equilibrium when all of these Hardy-Weinberg assumptions are met.

Fitness refers to the genetic contribution of an individual to succeeding generations compared to other individuals in the population. It measures the ability of an individual to survive, reproduce, and pass on its genes to the next generation. In evolutionary terms, fitness is a measure of how well an organism is adapted to its environment and how successful it is in producing offspring that can survive and reproduce. Therefore, fitness is the correct answer as it directly relates to the genetic contribution of an individual to future generations.

Darwin proposed that natural selection occurs in an environment by favoring heritable features that make the organism better suited to survive and reproduce. This means that individuals with advantageous traits are more likely to survive and pass on their genes to the next generation, while those with less advantageous traits are less likely to reproduce. Over time, this process leads to the accumulation of beneficial traits in a population, increasing its overall fitness and adaptability to the environment.

The correct answer is "bottleneck effect." The explanation for this answer is that the bottleneck effect refers to a situation where a population is drastically reduced in size due to a natural catastrophe or other event. As a result, the surviving individuals represent only a small, random sample of the original population's genetic diversity. This can lead to a loss of genetic variability and an increase in the frequency of certain traits or alleles in the population.

In directional selection, the population experiences a shift in the frequency of a particular trait towards one extreme. This means that individuals with a larger beak size, for example, have a higher chance of survival and reproduction compared to those with smaller beak sizes. Over time, this leads to an increase in the prevalence of the selected trait within the population, resulting in a strong selection for larger beak size.

The founder principle refers to a situation where a small group of individuals establishes a new population, resulting in a limited genetic diversity compared to the original population. Rare alleles, which are less common in the original population, may become more prevalent in the new population due to genetic drift. Therefore, the founder principle explains how rare alleles may become more common in new populations.

A locus with more variation than can be explained by mutation is referred to as polymorphic. This means that there are multiple forms or alleles of a gene present in a population. The variation at this locus cannot be solely attributed to mutations, indicating that there are other factors, such as genetic recombination or gene flow, contributing to the diversity at this particular gene locus.

The correct answer is p and q. In the Hardy-Weinberg equations, p represents the frequency of one allele in the population, and q represents the frequency of the other allele. These two alleles make up the entire gene pool of the population, so their frequencies can be designated as p and q.

The correct answer is Lamarck. Lamarck proposed the concept of the inheritance of acquired characteristics, which suggests that organisms can pass on traits acquired during their lifetime to their offspring. This idea was in contrast to Darwin's theory of natural selection, which focused on the inheritance of favorable variations through genetic mechanisms. Lamarck's proposal was eventually disproven by modern genetics, but it played a significant role in the development of evolutionary thought.

Disassortative mating refers to the preference for mating with individuals that are phenotypically different at various loci. This results in a higher number of heterozygotes in the population. This explanation aligns with the given statement that in some populations the drive is to mate with individuals that are phenotypically different, leading to large numbers of heterozygotes. Therefore, disassortative mating is the correct answer.

Artificial selection is not an agent of natural evolutionary change because it is driven by human intervention rather than natural processes. Natural evolution occurs through mechanisms such as mutation, migration, genetic drift, and non-random mating, which are all influenced by natural selection and environmental factors. In contrast, artificial selection involves deliberate selection and breeding of organisms with specific traits by humans for desired outcomes, such as in agriculture or animal breeding. This intentional manipulation of traits does not occur naturally and is not driven by the same forces as natural evolutionary change.

The correct answer is "there is very little genetic variability." This is because a genetic bottleneck occurs when a population is drastically reduced in size, leading to a loss of genetic diversity. As a result, there is very little variation in the genetic makeup of cheetahs, which is evidence of a genetic bottleneck in their history.

The text discusses sickle-cell anemia, which is a classic example of heterozygote advantage. This means that individuals who are heterozygous for the sickle-cell gene have an advantage over those who are homozygous for the gene. Heterozygotes are less likely to develop severe symptoms of sickle-cell anemia, but still have some protection against malaria, which is prevalent in areas where sickle-cell anemia is common. This advantage leads to a higher frequency of the sickle-cell gene in populations where malaria is endemic.

The founder effect is the phenomenon in which rare alleles become more common in new populations. This occurs when a small group of individuals establishes a new population, resulting in a limited gene pool. As a result, certain alleles that were rare in the original population may become more prevalent in the new population due to chance. This can lead to genetic differences between the original and new populations, as well as an increased likelihood of certain genetic disorders.

The California populations of the Northern elephant seal are descendants from a very small population of seals that was over-hunted in the 1890s. This event is known as a bottleneck, where the population size is drastically reduced, resulting in a loss of genetic diversity. As a result, heterozygosity, which refers to the presence of different alleles at a specific gene locus, would be expected to be slight in this population due to the bottleneck effect.

Assortative mating is a type of non-random mating where individuals with similar phenotypes or genotypes preferentially mate with each other. This can lead to an increase in the frequency of particular genotypes in the population, causing a deviation from the expected frequencies under Hardy-Weinberg equilibrium. In assortative mating, individuals with similar traits are more likely to reproduce together, which can result in an increase in homozygosity and a decrease in heterozygosity in the population. This type of non-random mating can cause significant changes in genotype frequencies and disrupt the genetic equilibrium.

not-available-via-ai

In disruptive selection, the most extreme outliers of a population are eliminated, resulting in the population being strongly selected for in two directions. This means that individuals with larger beak size and individuals with smaller beak size have a higher chance of survival and reproductive success, while individuals with intermediate beak sizes are at a disadvantage. This leads to an increase in the variation of beak sizes within the population.

Adaptations are features that increase the likelihood of survival and reproduction by an organism in a particular environment. These features can include physical traits, behaviors, or physiological mechanisms that allow an organism to better survive and reproduce in its environment. Adaptations are the result of natural selection, where individuals with traits that are advantageous in their environment are more likely to survive and pass on their genes to future generations.

In some instances, environmental change can lead to oscillating selection, where one phenotype is favored for a period of time, and then a different phenotype is favored. This oscillating selection helps in maintaining genetic variation in the population. It allows for the survival and reproduction of individuals with different traits, preventing the elimination of rarer genotypes and promoting diversity within the population.

Assortative mating refers to the tendency of individuals to choose mates that are similar to themselves in certain traits. This can lead to an increase in homozygosity within a population because individuals are more likely to mate with others who have the same alleles. In contrast, Hardy-Weinberg predictions assume random mating, which would result in a population with more heterozygotes. Therefore, populations that have practiced assortative mating would have more homozygotes compared to Hardy-Weinberg predictions.

Gene flow refers to the movement of genes from one population to another. This can occur through various means, such as migration and mating. In the given options, the correct answer is "hybridization between individuals of adjacent populations." This means that when individuals from different populations mate and produce offspring, the genes from one population are introduced into the gene pool of the other population through hybridization. This process allows for the exchange of genetic material and can lead to increased genetic diversity within populations.

Selection refers to the process by which certain traits or alleles become more or less common in a population over time. It occurs when individuals with advantageous traits have higher reproductive success and pass on those traits to their offspring. This leads to an increase in the frequency of the beneficial allele within the population. Selection can be driven by factors such as environmental pressures, competition for resources, or mate choice. In contrast, genetic outflow, large population size, inheritance of acquired characteristics, and random mating do not directly cause changes in allele frequency within a population.

Random mating is not an agent of evolutionary change because it does not lead to any changes in the genetic makeup of a population. In random mating, individuals mate with no preference for specific traits or characteristics, which means that there is no selection or change in allele frequencies. This results in the preservation of the existing gene pool and does not contribute to the introduction of new genetic variations or the elimination of existing ones. Therefore, random mating does not play a role in driving evolutionary change.

The Hardy-Weinberg equilibrium conditions state that in a population, allele frequencies will remain constant from generation to generation if certain conditions are met. These conditions include a large population size, random mating, no migration, no mutation, and no natural selection. When these conditions are met, the population will not experience any evolutionary changes, meaning that allele frequencies will not change over time. Therefore, the correct answer is "no evolutionary changes."

Directional selection occurs when selection acts to eliminate one extreme from an array of phenotypes. In this case, the selection is favoring individuals that possess a certain extreme phenotype, causing a shift in the average phenotype of the population towards that extreme. This type of selection can lead to evolutionary change as the population adapts to the new environmental conditions.

In small populations, there is a higher chance of random fluctuations in the frequency of certain alleles due to chance alone. This phenomenon is known as genetic drift. Genetic drift can lead to the loss or fixation of alleles in a population over time, and it is more pronounced in smaller populations where chance events can have a greater impact.

Mutation would be expected to produce the smallest evolutionary change in a given period of time in a population of birds. This is because mutation is a random and rare occurrence that introduces new genetic variations into a population. The effects of mutation are typically small and may not significantly impact the overall genetic makeup of a population in a short period of time. In contrast, natural selection, migration, assortive mating, and gene flow can all have more pronounced effects on the genetic composition of a population and lead to larger evolutionary changes.

Disassortive mating within a population could not be involved in gene flow because it refers to individuals within a population preferentially mating with individuals that are genetically dissimilar to themselves. This would result in reduced gene flow as individuals are not exchanging genetic material with a wide range of individuals in the population. Gene flow typically occurs when individuals migrate or disperse and mate with individuals from other populations, allowing for the exchange of genetic material.

The founder principle refers to the phenomenon where a small group of individuals establishes a new population, resulting in a limited gene pool and potentially leading to the increased frequency of certain alleles. In the given scenario, the small towns in the western United States have remained isolated and inbred since their settlement, indicating that they were founded by a small group of individuals. This limited gene pool and isolation have likely resulted in the increased frequency of certain alleles, making the founder principle the most appropriate explanation.

Given that about 80% of the alleles in thoroughbred horses can be traced back to a small number of ancestors, it suggests that there is limited genetic diversity in the population. This limited genetic diversity would result in little variation in physiology and behavior among thoroughbred horses.

In negative frequency-dependent selection, the incidence of predation leads to an increase in a rare genotype. This means that when a certain genotype becomes rare in a population, it becomes less likely to be preyed upon, giving it a survival advantage. As a result, the rare genotype increases in frequency within the population. This phenomenon helps to maintain genetic diversity and prevents any one genotype from dominating the population.

The statement that guppies transferred to pools above waterfalls remained drab if killifish were present there is false. According to the laboratory and field studies, guppies transferred to pools above waterfalls showed significant changes in their coloration, even in the presence of killifish. This suggests that the presence of killifish does not prevent the evolution of protective coloration in guppies.

Assortive and disassortive mating both affect the expected Hardy-Weinberg genotype frequencies in a population. Assortive mating occurs when individuals with similar phenotypes mate preferentially, leading to an increase in homozygosity. Disassortive mating, on the other hand, happens when individuals with dissimilar phenotypes mate preferentially, resulting in an increase in heterozygosity. Both types of mating change the distribution of genotypes in a population, but they do not directly affect the allele frequencies. Therefore, the correct answer is that assortive and disassortive mating change only the expected Hardy-Weinberg genotype frequencies in a population.