Chapter 20 Genes With Population

The total of all the alleles of all the genes in a population can be thought of as a gene pool. This is because a gene pool refers to all the genetic information present in a population, including all the different alleles for each gene. It represents the total genetic diversity within a population and serves as a reservoir from which individuals inherit their genetic traits. The term "allele mixture" is not commonly used in genetics, and "genetic melting pot" and "genome" do not accurately capture the concept of the total alleles in a population. "Variant genes" is also not an appropriate term as it does not encompass the entire genetic information present in a population.

The gene pool refers to the collection of all the different alleles of genes present in a population. It represents the genetic variation within a population, including all the different versions of genes that individuals possess. This genetic 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."

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 (a and A) with frequencies p and q respectively, the heterozygote genotype (Aa) can be formed in two ways: by choosing an allele A from the gene pool (probability p) and an allele a from the gene pool (probability q), or by choosing an allele a from the gene pool (probability q) and an allele A from the gene pool (probability p). Therefore, the probability of the heterozygote genotype is 2pq.

The correct answer is Darwin because he proposed the theory of natural selection as a mechanism of evolution. Darwin's theory states that individuals with traits that are advantageous for their environment are more likely to survive and reproduce, passing on those traits to future generations. Over time, this process leads to the evolution of different species. Mendel is known for his work on genetics, Lyell for his contributions to geology, and Malthus for his writings on population growth, but none of them proposed natural selection as a mechanism of evolution.

The bottleneck effect refers to a situation where a population experiences a significant reduction in size, resulting in a limited gene pool and reduced genetic variability. This can occur due to natural disasters, disease outbreaks, or human activities. The reduced genetic diversity can lead to a higher frequency of certain genetic traits and an increased risk of inbreeding. The founder effect, on the other hand, occurs when a small group of individuals establishes a new population, resulting in a loss of genetic variation compared to the original population.

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 those traits to their offspring, increasing the frequency of those traits in the population over time. This process leads to the adaptation of species to their environment, as traits that provide a survival and reproductive advantage become more common.

Natural selection is the correct answer because it refers to the process where certain individuals within a population possess genetic traits that increase their chances of survival and reproduction. These advantageous traits are then passed on to future generations, leading to the preservation of these features over time. This process is a fundamental mechanism of evolution and plays a crucial role in shaping the characteristics of a population.

Artificial selection is not an agent of natural evolutionary change because it is driven by human intervention rather than natural processes. In artificial selection, humans deliberately choose specific traits or characteristics in organisms and selectively breed them to produce offspring with desired traits. This differs from natural selection, where environmental factors determine which traits are advantageous for survival and reproduction. Therefore, artificial selection is not considered a natural process and does not contribute to the natural evolutionary changes that occur in populations over time.

The founder principle refers to the establishment of a new population by a small group of individuals who are not representative of the entire original population. This small group may carry rare alleles that were more common in the original population. As the new population grows and reproduces, these rare alleles can become more common within the population. Therefore, the founder principle explains how rare alleles may become more common in new populations.

The Hardy-Weinberg equations describe the genetic equilibrium in a population. This equilibrium is only achieved when all of the assumptions of the Hardy-Weinberg principle are met. These assumptions include a large population size, random mating, no mutation, no migration, and no natural selection. If any of these assumptions are violated, the population will not be in equilibrium. Therefore, the correct answer is when all of the Hardy-Weinberg assumptions are met.

The correct answer is the bottleneck effect. The bottleneck effect occurs when a population is drastically reduced in size due to a natural catastrophe or other event. This reduction in population size leads to a decrease in genetic diversity, as only a small, random sample of individuals survive and reproduce. As a result, the genetic composition of the population is altered, and certain alleles may become more or less common. This can have long-term effects on the population's genetic variability and ability to adapt to changing environments.

The correct answer is "there is very little genetic variability." This is because a genetic bottleneck refers to a sharp reduction in the size of a population, leading to a loss of genetic diversity. When a population goes through a genetic bottleneck, there is a decrease in the number of different genetic variations, resulting in very little genetic variability. This can be seen in cheetahs, as they have experienced a significant reduction in population size in the past, leading to a limited gene pool and low genetic diversity among individuals.

Lamarck proposed the theory of the inheritance of acquired characteristics, which suggests that organisms can pass on traits that they acquire during their lifetime to their offspring. This theory was later disproven by Darwin's theory of evolution through natural selection, which emphasized the role of genetic variation and hereditary traits in driving evolution. Wallace, Founder, and Hardy-Weinberg are not associated with the theory of the inheritance of acquired characteristics.

A locus with more variation than can be explained by mutation is referred to as polymorphic. Polymorphism refers to the presence of multiple forms or alleles of a gene within a population. In this context, it means that the locus has more variation than what can be attributed solely to mutations, indicating that there are multiple alleles present at that locus in the population.

Disassortative mating refers to the tendency of individuals to choose mates that are phenotypically different from themselves. This leads to an increase in heterozygotes within the population. This behavior can be advantageous as it promotes genetic diversity and can help maintain a balance between different alleles in the population. Neutral theory, shifting balance theory, bottleneck effect, and founder effect are not applicable in this context.

In the Hardy-Weinberg equations, the frequencies of two alleles in a population can be designated as p and q. These variables represent the frequency of the dominant and recessive alleles respectively. The equation assumes that there are only two alleles present in the population and that they are in Hardy-Weinberg equilibrium, meaning that the allele frequencies remain constant from generation to generation. By using p and q, the equation allows for the calculation of genotype frequencies and predictions about the inheritance patterns of traits in a population.

The correct answer is "slight; a bottleneck effect". The explanation for this is that the California populations of the Northern elephant seal are descendants from a very small population that was over-hunted in the 1890s. This over-hunting event is an example of a bottleneck effect, where the population size is drastically reduced, resulting in a decrease in genetic diversity. As a result, the heterozygosity in this population would be expected to be slight, indicating a lower level of genetic variation.

Selection refers to the process by which certain traits or alleles become more or less common in a population over time. It occurs when certain individuals with advantageous traits have a higher chance of survival and reproduction, passing on those traits to future generations. This leads to a change in the frequency of the allele within the population. Genetic outflow, large population size, inheritance of acquired characteristics, and random mating do not directly cause changes in allele frequency.

The founder effect refers to the phenomenon where rare alleles become more common in new populations. This occurs when a small group of individuals from a larger population establishes a new population, leading to a loss of genetic diversity. As a result, certain alleles that were rare in the original population may become more prevalent in the new population. This is due to the random sampling of alleles during the founding event, which can result in the increased frequency of certain alleles in subsequent generations.

In some instances, environmental change can create a situation where different phenotypes are favored at different times. This oscillating selection process helps to maintain genetic variation within the population. It allows for the survival and reproduction of individuals with different genetic traits, preventing the elimination of rarer genotypes and promoting diversity. This genetic variation is important for the long-term survival and adaptation of the population to changing environmental conditions.

The text discusses sickle-cell anemia, a genetic disorder caused by a point mutation in the hemoglobin gene. This mutation leads to the production of abnormal hemoglobin, resulting in the characteristic sickle-shaped red blood cells. However, individuals who are heterozygous for the sickle-cell gene have a selective advantage in regions where malaria is prevalent. Malaria parasites cannot survive as well in these heterozygous individuals, providing a survival advantage. Therefore, the correct answer is heterozygote advantage.

Fitness refers to the genetic contribution of an individual to succeeding generations compared to other individuals in the population. It is a measure of an organism's ability to survive and reproduce in its environment, taking into account factors such as reproductive success and the passing on of advantageous traits. Fitness is a key concept in evolutionary biology, as individuals with higher fitness are more likely to pass on their genes to future generations, leading to the adaptation and evolution of populations over time.

Assortative mating is a type of non-random mating where individuals with similar phenotypes or genotypes mate preferentially. This leads to an increase in the frequency of particular genotypes in the population, causing a deviation from the expected frequencies under Hardy-Weinberg equilibrium. This type of mating can result in an increase in homozygosity and a decrease in heterozygosity within the population. It can occur based on physical traits, behavior, or other characteristics that individuals find attractive in potential mates.

Adaptations are features that increase an organism's chances of survival and reproduction in a specific environment. These adaptations can be physical, behavioral, or physiological traits that allow the organism to better cope with its surroundings. Genes, mutations, and selection are all factors that can contribute to the development of adaptations, but adaptations themselves are the specific features that provide an advantage in a given environment.

The Hardy-Weinberg principle states that the proportions of genotypes in a population will remain constant if certain conditions are met. These conditions include a large population size, no gene flow, no selection, random mating, and the presence of polymorphic loci (multiple alleles) in the population. The absence of polymorphic loci would mean that there is only one allele for each gene in the population, which violates the condition of genetic variation necessary for the Hardy-Weinberg equilibrium.

Gene flow refers to the movement of genes from one population to another. This can occur through various mechanisms, including migration and mating with individuals who possess certain traits. However, in the given options, the most appropriate explanation for gene flow would be hybridization between individuals of adjacent populations. Hybridization occurs when individuals from different populations interbreed and produce offspring with a combination of genetic traits from both populations. This process leads to the transfer of genes between populations, resulting in gene flow.

The fact that about 80% of the alleles in thoroughbred horses can be traced back to a small number of ancestors suggests that there has been limited genetic diversity introduced through mutation over time. This limited genetic diversity would result in little variation in physiology and behavior among thoroughbred horses.

Directional selection occurs when selection acts to favor individuals with phenotypes that are at one extreme of the range of variation. In this case, one extreme phenotype is being eliminated by selection. This is different from stabilizing selection, which favors individuals with intermediate phenotypes, disruptive selection, which favors individuals with extreme phenotypes at both ends of the range, and artificial selection, which is the result of intentional breeding by humans. Therefore, the correct answer is directional selection.

In small populations, the frequencies of certain alleles can change randomly due to chance events. This phenomenon is known as genetic drift. Genetic drift occurs when certain alleles become more or less common in a population over time without any selective pressure. It is a result of random sampling and can lead to the loss or fixation of certain alleles in a population. Migration refers to the movement of individuals between populations, mutation refers to the introduction of new genetic variations, nonrandom mating refers to mating preferences that are not based on chance, and selection refers to the process by which certain traits are favored or disfavored in a population based on their fitness.

Random mating is not an agent of evolutionary change because it does not cause any changes in the genetic makeup of a population. In random mating, individuals choose their mates without any preference for specific traits or characteristics, and there is no selection or bias involved. Therefore, random mating does not lead to any changes in the frequency of alleles or genetic variation within a population over time.

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, increasing its chances of survival and reproduction. As a result, the frequency of this rare genotype increases over time. This mechanism helps to maintain genetic diversity within a population, as rare genotypes have a selective advantage in avoiding predation.

Disassortive mating within a population could not be involved in gene flow because it refers to a mating pattern where individuals with different traits or characteristics preferentially mate with each other. This can lead to the separation of different genetic variants within a population, reducing gene flow between individuals with different traits. Gene flow typically occurs when individuals or their gametes physically move between populations, allowing for the exchange of genetic material.

The founder principle refers to the effect where certain small towns in the western United States have remained isolated and inbred since their settlement many years ago, leading to some alleles being more common in these communities compared to the rest of the population. This phenomenon is not due to artificial selection, directional selection, disrupting selection, or the Hardy-Weinberg principle, but rather the result of the founder principle.

In disruptive selection, the most extreme outliers of a population are eliminated, leading to the population being strongly selected for in two directions. This means that both larger beak size and smaller beak size are favored, resulting in an increase in the variation of beak sizes within the population. This phenomenon can occur when different traits provide advantages in different environmental conditions, causing the population to diverge into two distinct groups with contrasting traits.

Assortative mating refers to the tendency of individuals to choose mates with similar traits. In populations that practice assortative mating, individuals with similar genotypes are more likely to mate, leading to an increase in homozygosity. This is because individuals with similar genotypes are more likely to pass on the same alleles to their offspring, resulting in an increase in homozygotes. Therefore, compared to Hardy-Weinberg predictions, populations that practice assortative mating will have more homozygotes.

not-available-via-ai

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 process that introduces new genetic variations into a population, but it does not necessarily result in significant changes in the overall genetic makeup of the population. Natural selection, migration, assortive mating, and gene flow, on the other hand, can all lead to significant changes in the genetic composition of a population over time.

The Hardy-Weinberg equilibrium conditions state that in a population, allele and genotype 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. If these conditions are met, the population will be in equilibrium and there will be no changes in allele frequencies. Therefore, the correct answer is "no evolutionary changes."

In directional selection, the population is strongly selected for in two directions, such as larger beak size and smaller beak size. This means that individuals with beaks that are either larger or smaller than the average beak size have a higher chance of survival and reproduction. Over time, this can lead to a decrease in individuals with average beak sizes and an increase in individuals with either larger or smaller beak sizes, resulting in a population that is strongly selected for in two directions.

Assortive and disassortive mating both refer to non-random mating patterns in a population. Assortive mating occurs when individuals with similar traits mate with each other more often than would be expected by chance, while disassortive mating occurs when individuals with dissimilar traits mate with each other more often than expected. Both types of mating patterns affect the genotype frequencies in a population, but they do not change the allele frequencies. Therefore, the correct answer is that both assortive and disassortive mating change only the expected Hardy-Weinberg genotype frequencies in a population.