Question

The Hardy-Weinberg equation characterizes the allele and genotype frequencies a. of a population that is experiencing selection for mating success. b. of a population that is extremely small. c. of a population that is very large and not evolving. d. of a community of species that is not evolving. e. of a community of species that is experiencing selection.

Short answer

The Hardy-Weinberg equilibrium characterizes the allele and genotype frequencies of a population that is very large and not evolving. Hence, the correct answer is statement C.

Step-by-step solution

Evaluate Statement A

Statement A suggests the Hardy-Weinberg equation characterizes a population experiencing selection for mating success. However, under Hardy-Weinberg conditions, mating is random and not subject to any selection. Hence, this statement is false.

Evaluate Statement B

Statement B suggests the equation characterizes a small population. This is incorrect as one of the assumptions of Hardy-Weinberg equilibrium is a large population size, therefore avoiding genetic drift. Hence, this statement is also false.

Evaluate Statement C

Statement C suggests the equation characterizes a very large population that is not evolving. This is in fact true, as it aligns with the basic assumptions of the Hardy-Weinberg equilibrium principle, which is that the population is very large and mutation, migration and natural selection are not happening, thereby leading to a not evolving population.

Evaluate Statement D

Statement D is about a community of species that is not evolving. However, Hardy-Weinberg equilibrium is used to describe a single population, not a community of multiple species. Therefore, this statement is inaccurate.

Evaluate Statement E

Statement E, which indicates a community experiencing selection, contradicts the condition of Hardy-Weinberg equilibrium that there is no selection. Therefore, this statement is also false.

Key concepts

Genetic Drift

Genetic drift refers to random changes in allele frequencies that occur in small populations. It arises from the statistical fluctuations that can happen when alleles are passed from one generation to the next, and is especially prominent when the number of individuals is limited. Unlike natural selection, which is a non-random process, genetic drift does not necessarily result in adaptations to the environment.

Imagine flipping a coin. If you flip it 10 times, you may not get exactly 5 heads and 5 tails due to chance. This randomness is similar to genetic drift - in small populations, some alleles can become more or less common just by chance, leading to potentially significant changes over time. If an allele becomes very rare, genetic drift can even lead to its complete loss from the population, reducing genetic variation.

Allele and Genotype Frequencies

Allele frequency is the proportion of all copies of a gene in a population that a specific allele constitutes. For example, if a gene has two possible alleles, A and a, and there are 100 copies of this gene within a population with 70 A alleles and 30 a alleles, then the frequency of allele A is 0.7 and the frequency of allele a is 0.3.

Genotype frequency, on the other hand, refers to the proportion of the population that carries a particular combination of alleles. Continuing the above example, if 49 individuals are AA, 42 are Aa, and 9 are aa out of 100 individuals, then the frequencies of the genotypes AA, Aa, and aa would be 0.49, 0.42, and 0.09, respectively. Hardy-Weinberg equilibrium provides a way to predict the genotype frequencies based on allele frequencies under certain ideal conditions.

Population Genetics

Population genetics is the study of distributions and changes of allele frequency in a population, as the population is subject to the four main evolutionary processes: mutation, selection, gene flow, and genetic drift. It merges Darwin's theory of natural selection with Mendelian genetics. A central idea in population genetics is that allele and genotype frequencies in a population will remain constant from one generation to the next in the absence of disturbing factors.

The Hardy-Weinberg equilibrium is a key concept in population genetics that serves as a null hypothesis for studying evolutionary processes. If a population is observed to deviate from what is expected under Hardy-Weinberg equilibrium, it suggests that one or more of the underlying assumptions (like random mating, large population size) have been violated, and some form of evolutionary force is acting on the population.

Non-evolving Population

A non-evolving population is one in which allele and genotype frequencies do not change over time. This indicates that the population is in Hardy-Weinberg equilibrium and not subject to evolutionary forces such as natural selection, genetic drift, mutation, or gene flow. In practice, no natural population fully meets these conditions, but Hardy-Weinberg provides a useful model for a theoretically stable population.

The five conditions for a non-evolving population under Hardy-Weinberg equilibrium are: very large population size (to minimize genetic drift), no mutations, random mating, no gene flow, and no selection. By comparing real populations against this model, scientists can infer which evolutionary forces may be in play, which is crucial for understanding how populations change over time.