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Chapter 8: Problem 5

The theory of neutral evolution describes a. the rate of mutation at a site that results from purifying selection, regardless of the size of the population. b. the rate of fixation of alleles at a site in the absence of selection. c. the competition between genetic drift and natural selection within the genome. d. Both a and b.

Short Answer

Expert verified
Option B is the correct answer.

Step by step solution

01

Understand Key Concepts

Before we analyze the options, let's understand the key terms: 'neutral evolution,' 'mutation,' 'purifying selection,' 'fixation of alleles,' and 'absence of selection'. Neutral evolution suggests that most evolutionary changes are the result of genetic drift of mutant alleles that are neutral. This is unlike changes driven by natural selection.
02

Analyze Option A

Option A suggests the theory describes the rate of mutation due to purifying selection. Purifying selection involves eliminating deleterious mutations rather than fixing them, which contradicts the neutral theory framework, as neutral theory doesn't typically incorporate purifying selection.
03

Analyze Option B

Option B states the focus is on the rate of fixation of alleles in the absence of selection. This aligns well with the theory of neutral evolution, as it centers on genetic drift (random fluctuation) rather than selection in allele fixation.
04

Analyze Option C

Option C mentions competition between genetic drift and natural selection. The theory of neutral evolution posits that most allele changes are neutral and driven by drift rather than selection, so this option is slightly misleading.
05

Determine the Correct Answer

Considering the analysis of each option, option B accurately describes the focus of the theory of neutral evolution by specifying fixation rates in the absence of selection, which aligns with neutral theory principles.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Genetic Drift
Genetic drift is one of the fundamental concepts in population genetics. It refers to the random fluctuations in the frequency of alleles (gene variants) in a population. These fluctuations are not caused by natural selection, but by chance.
In smaller populations, genetic drift can have a more pronounced effect. For example, if a disease wipes out individuals carrying a specific allele randomly, the frequency of this allele will decrease.
Over time, genetic drift can lead to the fixation or loss of alleles in a population, contributing to the genetic diversity between populations.
  • Genetic drift operates randomly and independently from natural selection.
  • The effect of genetic drift is stronger in small populations.
  • It can lead to significant evolutionary changes over time.
Mutation
Mutations are changes in the DNA sequence of an organism's genome and serve as a primary source of genetic variation. Without mutations, evolution would not have the raw material to work with.
Mutations can occur due to errors during DNA replication, exposure to certain chemicals, or environmental factors like radiation.
  • Some mutations are neutral, meaning they do not affect an organism's fitness.
  • Others can be beneficial or deleterious, impacting how natural selection acts on them.
  • Neutral mutations contribute to genetic drift.
Most mutations are neutral or slightly deleterious, with a smaller percentage being beneficial.
Purifying Selection
Purifying selection, also known as negative selection, is the process by which deleterious mutations are removed from the gene pool. This helps maintain the integrity of a species' genetic makeup.
When a mutation negatively affects an organism鈥檚 ability to survive or reproduce, purifying selection reduces its frequency in the population.
It plays a crucial role in preventing harmful mutations from becoming common.
  • Purifying selection contrasts with positive selection, where beneficial mutations are favored.
  • It is an ongoing process acting to preserve optimal traits in a population.
  • This form of selection reduces genetic variation within a population.
Allele Fixation
Allele fixation occurs when a particular version of a gene (allele) becomes the only allele in a population. This means all individuals in the population are homozygous for that allele.
Fixation can happen due to genetic drift or natural selection; in neutral evolution, it happens by the random processes of genetic drift.
When an allele reaches fixation, genetic diversity at that locus is lost.
  • Allele fixation is more likely in small populations due to stronger genetic drift effects.
  • In larger populations, selection pressures usually prevent fixation unless the allele offers some advantage.
  • Fixation is a key concept in understanding evolutionary dynamics and genetic drift.

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Most popular questions from this chapter

Why might humans and dogs have used the same genes when they locally adapted to high elevation populations?

Why are conserved genes important when developing phylogenies?

Which of these is a true statement about molecular clocks? a. Molecular clocks use neutral theory to date events within a phylogeny. b. Molecular clocks can be calibrated using fossils of known age. c. Molecular clocks can be affected by the segments of DNA being examined and relative sizes of the populations. d. All of the above.

Discuss the differences between a gene tree and a species tree.

Which of the following is not true of the neutral theory of molecular evolution? a. When neutral variation accumulates at a steady rate, the molecular signature generated is an unreliable measure to date events in the distant past. b. The neutral theory of molecular evolution describes the pattern of nucleotide sequence evolution under the forces of mutation and random genetic drift in the absence of selection. c. The neutral theory predicts that neutral mutations will yield nucleotide substitutions in a population at a rate equivalent to the rate of mutation, regardless of the size of population. d. As long as mutation rates remain constant, neutral variation is expected to accumulate at a steady rate.
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