Question

Why isn't inbreeding considered an evolutionary process? a. It does not change genotype frequencies. b. It does not change allele frequencies. c. It does not occur often enough to be important in evolution. d. It does not violate the assumptions of the Hardy-Weinberg principle.

Short answer

Inbreeding is not considered an evolutionary process because it does not change allele frequencies within a population (option b).

Step-by-step solution

Define Inbreeding and Evolutionary Process

Inbreeding is the mating of closely related individuals, which results in an increased probability that offspring will inherit the same alleles from both parents for a given gene. An evolutionary process is a mechanism that causes changes in genetic and phenotypic variations within a population, which may eventually lead to speciation or adaptation.

Examine Option (a)

Option (a) states that inbreeding "does not change genotype frequencies." Inbreeding actually does change genotype frequencies, increasing homozygosity and decreasing heterozygosity. Thus, option (a) is not the correct answer.

Examine Option (b)

Option (b) states that inbreeding "does not change allele frequencies." This is correct. Inbreeding does not cause any new alleles to be created or existing alleles to be lost; it simply changes how often certain combinations of alleles are present together in an organism (i.e., the genotype). This lack of change in allele frequencies is a key reason why inbreeding is not considered an evolutionary process.

Examine Option (c)

Option (c) states that inbreeding "does not occur often enough to be important in evolution." Inbreeding can occur in various situations, such as in small, isolated populations. Although it may not be the primary driver of evolution, it can still have a significant impact on populations under certain circumstances. Thus, option (c) is not the correct answer.

Examine Option (d)

Option (d) states that inbreeding "does not violate the assumptions of the Hardy-Weinberg principle." The Hardy-Weinberg principle assumes that there is random mating in a population. Inbreeding, by definition, is non-random mating. Thus, inbreeding actually does violate one of the assumptions of the Hardy-Weinberg principle, so option (d) is not the correct answer.

Conclusion:

After analyzing each option, we can conclude that the correct answer is (b). Inbreeding is not considered an evolutionary process because it does not change allele frequencies within a population.

Key concepts

Genotype Frequencies

Genotype frequencies refer to how often different genetic combinations occur within a population. These frequencies are expressed as proportions and represent the diversity of genetic traits present. In the context of inbreeding, the mating of closely related individuals generally increases the frequency of homozygous genotypes (where offspring receive the same allele from both parents). This change in genotype frequencies can lead to a decrease in genetic diversity.

However, it's important to distinguish between genotype frequencies and evolutionary change. Evolution requires not only a shift in genetic combinations but also alterations in the actual alleles present within a gene pool over time. In the case of inbreeding, while it changes genotype frequencies by increasing homozygosity, it does not create new alleles or eliminate existing ones.

Allele Frequencies

Allele frequencies, on the other hand, denote how common a certain form of a gene is in a population. Unlike genotype frequencies that deal with combinations of alleles, allele frequencies purely count how many times a specific allele appears, regardless of the genotype it's part of. It's a critical distinction because evolutionary processes are typically reflected in changes to allele frequencies within a gene pool.

Inbreeding does not introduce such changes; it merely redistributes existing alleles into different genotypic combinations without affecting their overall prevalence in the population. Hence, inbreeding doesn't constitute an evolutionary process as it doesn't lead to alteration in allele frequencies which are necessary for a population's genetic makeup to evolve.

Hardy-Weinberg Principle

The Hardy-Weinberg principle is fundamental to understanding why inbreeding isn't considered an evolutionary process. This principle states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences, provided that certain assumptions are met, including random mating, large population size, no mutation, no migration, and no selection.

Inbreeding, by its nature, involves non-random mating, but it doesn't itself cause changes in allele frequencies. It, therefore, violates one of the Hardy-Weinberg assumptions, but the violation alone does not result in evolution. The principle helps us to understand the underlying conditions needed for a population's allele and genotype frequencies to stay in equilibrium, hence serving as a reference point for identifying factors that can cause evolution.

Evolutionary Mechanisms

Evolutionary mechanisms are processes that alter genetic variation and contribute to evolution within populations. These mechanisms include natural selection, genetic drift, mutation, and gene flow.

Each mechanism has distinct effects on allele frequencies. Natural selection favors certain alleles based on their contribution to survival and reproduction, genetic drift causes random fluctuations in allele frequencies, mutations introduce new alleles into a population, and gene flow occurs when individuals migrate between populations, causing allele frequencies to change due to the introduction or loss of alleles. Inbreeding doesn't generate these allelic changes and therefore isn't an evolutionary mechanism.

Speciation

Speciation is the formation of new and distinct species in the course of evolution. It generally occurs due to the reproductive isolation of populations, which can result from geographical barriers, behavioral differences, or other factors that prevent gene flow.

Over time, this isolation can lead to the evolution of different traits and the emergence of distinct species. While inbreeding can increase homogeneity within a population and could potentially contribute to reproductive isolation, it is not, in itself, a process that causes the genetic divergence necessary for speciation.

Adaptation

Adaptation is a process where a population becomes better suited to its habitat through changes in its genetic composition. This change often occurs through natural selection, where certain alleles that confer a survival or reproductive advantage become more common over time.

Inbreeding can have a role in adaptation if it happens to increase the prevalence of alleles that are beneficial in a particular environment. However, it is not considered a primary driver of adaptation because it does not inherently select for beneficial traits; instead, it increases genetic uniformity. True adaptation involves the preferential survival and reproduction of individuals with certain advantageous traits, which is not the direct result of inbreeding.