Microevolution

Evolution and Individuals

Do individuals evolve? Explain

No, individuals do not evolve. Evolution occurs in populations over generations. It involves changes in the frequency of alleles (gene variants) in a population over time.

Microevolution Concepts

Explain what microevolution is using an example.

Microevolution refers to small, short-term changes in the allele frequencies within a population. Example: A population of beetles where the frequency of brown beetles increases because they are better camouflaged against predators than green beetles.

Explain the idea of gradualism.

Gradualism suggests that evolution occurs slowly and steadily through small changes over long periods of time.

Define the terms population and species.

Population: A group of individuals of the same species that live in the same area and interbreed.
Species: A group of organisms that can interbreed and produce fertile offspring under natural conditions.

Explain what is meant by a gene pool.

A gene pool is the total collection of genes (and their alleles) in a population, representing all genetic material available for evolution.

Explain what a fixed allele is.

A fixed allele is an allele that is the only variant in a population, meaning it has a frequency of 100% in that population.

Theories and Principles

Explain the theory of population genetics.

Population genetics studies the genetic makeup of populations and how it changes over time due to factors like natural selection, mutation, gene flow, and genetic drift.

Explain the theory of modern synthesis.

The modern synthesis combines Darwin’s theory of natural selection with Mendelian genetics, showing that evolutionary changes occur due to genetic variations and mutations passed on through generations.

Give the last names of the architects of modern synthesis.

Fisher, Haldane, Wright, and Mayr are some of the main figures associated with the modern synthesis.

Give the three main points of emphasis of the modern synthesis.

  1. Genetic variation is the raw material for evolution.

  2. Natural selection acts on genetic variation.

  3. Populations, not individuals, evolve over time.

Hardy-Weinberg Theorem

Explain what the Hardy-Weinberg Theorem describes.

The Hardy-Weinberg Theorem states that allele frequencies in a population will remain constant (in equilibrium) from generation to generation unless certain evolutionary forces are acting on the population.

What do p and q represent in the Hardy-Weinberg Theorem?

p = frequency of the dominant allele.
q = frequency of the recessive allele.

Give the formulas for the combined frequencies of each allele.

\( p + q = 1 \) (The total allele frequency is 100%)
For genotype frequencies: \( p^2 + 2pq + q^2 = 1 \)

  • \( p^2 \) = frequency of homozygous dominant (AA)

  • \( 2pq \) = frequency of heterozygous (Aa)

  • \( q^2 \) = frequency of homozygous recessive (aa)

Explain how the Hardy-Weinberg Theorem plugs a hole in Darwin's theory.

Hardy-Weinberg showed that genetic variation can remain stable in a population if no evolutionary forces are acting, which provided a clearer mechanism for the inheritance of traits (via alleles).

Give the 5 conditions Hardy-Weinberg must satisfy.

  1. No mutation

  2. No gene flow (migration)

  3. Random mating

  4. Large population size (no genetic drift)

  5. No natural selection

Hardy-Weinberg Criteria

Factors Violating Hardy-Weinberg

No. All four factors (natural selection, mutation, genetic drift, and gene flow) violate one or more of the Hardy-Weinberg assumptions, meaning they can cause evolution and alter allele frequencies.

Natural Selection

Adaptation to Environment

Natural selection is the only factor that consistently increases the frequency of advantageous traits in a population, making individuals better suited to their environment. The other factors (mutation, genetic drift, gene flow) don't necessarily lead to traits that improve an organism's fitness in its environment.

Natural Selection and Offspring

Natural selection favors individuals with traits that increase their chances of survival and reproduction. For example, in a population of giraffes, individuals with longer necks may be better at reaching food in tall trees, giving them a survival advantage. These individuals are more likely to reproduce and pass on their genes to the next generation, leading to an increase in the frequency of the long-neck allele.

Wildflowers Example

In a population of wildflowers, assume there are two colors of flowers: red and white. The red flowers are better camouflaged from herbivores, while the white flowers are more easily eaten. Over time, the red flowers will likely survive more often and produce more offspring, increasing the frequency of the red allele in the population due to natural selection.

Genetic Drift

Concept of Genetic Drift

Genetic drift is the random fluctuation of allele frequencies in a population, particularly in small populations. It occurs by chance rather than natural selection.

Example of Genetic Drift

In a small population of beetles, a random event (like a storm) could kill off individuals of one color (e.g., green beetles), changing the allele frequencies without regard to fitness.

Sampling Errors

Sampling errors occur when a sample (like a small population) does not accurately represent the whole population, leading to random changes in allele frequencies. Example: In a small group of individuals, one allele might be overrepresented or underrepresented simply due to chance.

Coin Toss Analogy

A coin toss is a simple random event with two possible outcomes (heads or tails). The results of several coin tosses (if not enough trials) might not perfectly represent the expected 50-50 distribution of heads and tails. Similarly, in small populations, random genetic changes can occur purely by chance, leading to allele frequencies that may not represent the actual population's true genetic makeup.

Effect of Genetic Drift on Small Sample Size

In a population of 10 butterflies with two alleles for wing color (red and blue), a random event could eliminate most of the butterflies with blue wings. This would drastically alter the allele frequencies, even though there was no selective advantage to red wings. This change in allele frequencies is due to genetic drift, and it could lead to a loss of genetic diversity in the population.

Bottleneck and Founder Effects

Bottleneck Effect

The bottleneck effect occurs when a population undergoes a drastic reduction in size due to an environmental event (like a fire, earthquake, or disease), leading to a loss of genetic diversity. Example: A population of 100 cheetahs experiences a drought, and only 10 cheetahs survive. If the survivors' alleles do not represent the entire original population, the gene pool has been drastically reduced, resulting in reduced genetic diversity.

Founder Effect

The founder effect occurs when a small group of individuals from a larger population colonizes a new area. This small group may carry only a subset of the genetic diversity of the original population, leading to reduced genetic variation in the new population. Example: A few birds from a large mainland population of sparrows migrate to a distant island. Over time, the island population may become genetically different from the mainland population because it was started by only a few individuals (the 'founders'), and their alleles were overrepresented.

Gene Flow and Mutation

Concept of Gene Flow

Gene flow (also called migration) is the transfer of genetic material between different populations of the same species. It occurs when individuals from different populations interbreed, introducing new alleles into the gene pool. Example: If a population of frogs from one pond migrates to a nearby pond, they may interbreed with the resident frogs, introducing new alleles into the population.

Reducing Differences in Populations

Gene flow reduces differences between populations by increasing genetic similarity. When individuals from different populations interbreed, they introduce alleles that may not have been present in one of the populations, making the populations genetically more similar over time.

Concept of Mutation

A mutation is a change in the DNA sequence of an organism's genome. Mutations can introduce new alleles into the gene pool, increasing genetic variation in a population. If a mutation is beneficial, it may increase in frequency through natural selection. If harmful, it may be eliminated over time.

Single Locus Mutation Impact

A single locus mutation may or may not have a measurable effect on a population. If the mutation occurs in a critical gene, it could have a significant impact on an individual’s fitness, and the allele may increase or decrease in frequency. However, most mutations are neutral and may not have an immediate effect on the population's gene pool.

Cumulative Impact

Cumulative impact refers to the idea that the combined effects of multiple small changes, such as mutations, can lead to significant evolutionary shifts over long periods of time. This could involve genetic changes in many loci across the genome, which accumulate and may significantly affect the population's traits.

Gene Mutations as Raw Material

Gene mutations are the source of genetic variation in populations. Without mutations, there would be no new alleles for natural selection to act upon. Mutations provide the 'raw material' for evolution by creating new traits, some of which may be advantageous, allowing individuals with those traits to survive and reproduce more successfully.