The Theory of Evolution: Mechanisms and Processes

Evolution

Change in frequency of heritable characteristics of biological populations over successive generations.

Allele Frequency

How common is the allele? What percentage of the population has that characteristic?

Requirements of Evolution

Heritable Genetic Variation, Different alleles present, Heredity of traits.

Mechanisms of Evolution

Processes include Natural Selection, Genetic Drift, and Mutation.

Natural Selection

A mechanism of evolution proposed by Darwin.

Genetic Drift

A mechanism of evolution that involves random changes in allele frequencies.

Mutations

A technicality in the mechanisms of evolution that introduces new alleles.

Populations vs. Individuals

Populations evolve, individuals do not.

Heritable Genetic Variation

Genetic variation that is passed from parent to offspring.

Sources of Genetic Variation

Recombination, Independent Assortment, Mutation in Gametes, Gene Flow, Non-random Mating.

Recombination

A source of genetic variation that occurs during crossing over.

Independent Assortment

A source of genetic variation that occurs during gamete formation.

Gene Flow

Movement of individuals to new places that introduces new alleles.

Non-Random Mating

When some mates are preferred over others, affecting allele frequencies.

Allele Frequency Change

If the proportion of the population with an allele is different at different times, evolution occurs.

Homozygous

An individual with two identical alleles for a characteristic.

Evolution Requires Genetic Variation

No change in allele frequency = NO EVOLUTION.

Allele Frequency of W

If all plants have W allele only, allele frequency of W = 1 (or, 100%).

Heritable Characteristics

Characteristics transmitted to the next generation with a genetic basis coded in DNA.

Non-Genetic Influences

Some characteristics, like height, can be influenced by factors such as nutrition.

Gene Pool

The total collection of alleles in a population.

Migration and Gene Flow

When an individual from one population migrates to another and reproduces, introducing new alleles.

Assortative mating

Mating preference for organisms that are similar to themselves.

Disassortative mating

Mating preference for organisms that are different from themselves.

Mutations

The original source of ALL genetic variation.

New allele

A result of mutations that can occur, although most mutations do not result in new alleles due to redundancy in the genetic code.

Germ cell mutation

A mutation that can be inherited by offspring.

Somatic cell mutation

A mutation that WILL NOT BE inherited by offspring.

Evolution

Change in allele frequency in a population over time.

Fixed allele

An allele that has a frequency of 100%, meaning it is the ONLY allele in the population.

Maintained allele

An allele that has a frequency between 0% and 100%.

Lost allele

An allele that has a frequency of 0%, meaning none of that allele exists in the population.

Charles Darwin

Naturalist who published 'On the Origin of Species' in 1859, detailing evolution via natural selection.

Galapagos Island Finches

Different species of finches that adapted to their environments, showcasing descent with modification.

Fitness

An organism's ability to survive and reproduce.

Adaptation

The heritable trait that enhances an organism's fitness.

Heritable genetic variation

A requirement for evolution, where different alleles must be present.

Overproduction

A requirement of natural selection where there are not enough resources for everyone.

Selection Pressure

The degree to which fitness increases due to a beneficial allele.

Survival of the (Biologically) Fittest

The concept that individuals with favored alleles reproduce more and have higher fitness.

Beneficial allele

An allele that increases the fitness of the individual.

Camouflage

An example of a trait that allows an organism to avoid predators.

Peppered Moths

A species that changed in allele frequency due to environmental changes during the industrial revolution.

White rabbits

An example of a trait that decreases in frequency in polluted environments due to predation.

Dark rabbits

An allele associated with increased fitness in polluted environments.

Environmental conditions

Factors that favor some allele(s) over others in natural selection.

Natural Selection

The process where individuals with favorable traits reproduce more than those without, leading to changes in allele frequencies over time.

Alleles

Different forms of a gene that can exist at a particular locus in a population.

Higher Fitness

Individuals with the favored allele reproduce more, leading to an increase in that allele's frequency.

Lower Fitness

Individuals with the non-favored allele reproduce less, leading to a decrease in that allele's frequency.

Genetic Drift

A random process that causes allele frequencies to change in a population, especially strong in smaller populations.

Sampling Error

The chance events that affect which individuals reproduce and which alleles are passed to the next generation.

Bottleneck Effect

An extreme reduction in population size due to catastrophic events, leading to different allele frequencies in the surviving population.

Founder Effect

A mechanism of genetic drift that occurs when a small group starts a new population, resulting in different allele frequencies than the original population.

Environmental Conditions

Factors that can favor one allele over others, influencing natural selection.

Allele Frequencies

The relative frequency of an allele at a genetic locus in a population.

Population Size

The number of individuals in a population, which affects the strength of genetic drift.

Small Populations

Populations where genetic drift has a stronger effect, leading to quicker changes in allele frequencies.

Large Populations

Populations where genetic drift has a weaker effect, leading to slower changes in allele frequencies.

Extreme Genetic Drift

Significant changes in allele frequencies due to random events, such as the Bottleneck Effect.

Natural Selection vs Genetic Drift

Natural selection can lead to faster changes in allele frequencies when one allele is favored, while genetic drift leads to random changes regardless of allele benefit.

Allele Benefit or Harm

The impact an allele has on an individual's fitness, which does not affect genetic drift.

Reproduction in Small Populations

In small populations, the chance of all individuals with a certain allele not reproducing is higher.

Reproduction in Large Populations

In large populations, it is less likely that all individuals with a certain allele do not reproduce.

Catastrophic Events

Events that can lead to a Bottleneck Effect by drastically reducing population size.

Random Survivors

In a Bottleneck Effect, the individuals that survive and reproduce are chosen randomly, regardless of their alleles.

Allele Frequencies Post-Bottleneck

After a bottleneck event, the allele frequencies in the surviving population differ from those in the original population.

Colonization

The process by which a small group of individuals starts a new population in a different area, leading to the Founder Effect.

Equal Fitness

When individuals with different alleles have the same ability to survive and reproduce, leading to evolution only through genetic drift.

Selective Pressure

The influence of environmental factors on the survival and reproduction of individuals with certain alleles.