2026-05-19 06:24

Status: #new

Tags: #biology #genetics

5.4 Modes of Evolution

Factors for Change to the Gene Pool

• Genetic Drift - Chance Fluctuations can cause change
• Non-Random Mating Opportunities - Preferred individuals pass on their alleles in greater numbers than others
• Genetic Mutation - New alleles are created or alleles are changed
• Gene Flow - Alters alleles within populations
• Natural Selection - Individuals with certain alleles have higher fitness than others, increasing these individuals allele frequencies in the gene pool

Modes for Evolution

• These are factors that lead to changes in populations

Mutation

• Mutation is the primary source of variation in a population
• The rate of mutation occurring is proportional to the size of an population
• While alot of Mutations are neutral (do not affect reproductive success), non-neutral mutations are subject to natural selection
• The more mutations that occur, the higher the genetic diversity
• Events are random and must occur in gametes in order to affect offspring

Gene Flow

• Gene Flow refers to how alleles can travel between populations. This occurs when organisms immigrate or emigrate (migration).
• When organisms migrate, leaving one population to join an other, they alter the allele frequencies of both populations
  • Such that, Genetic Information is shared between populations

Non-Random Mating

• Organism selection of mates based on preferred characteristics or due to inbreeding
  • Selected for physical or behavioural traits

Issues with Non-Random mating

• Self-Fertilization/Inbreeding can occur
• This is where close relatives share similar genotypes, such that inbreeding increases the frequency of homozygous genotypes
• As homozygous genotypes become more common, harmful recessive alleles are alot more likely to be expressed.

Some Examples

• A number of insects chose mates based off physical similarities
• Plants, self-fertilization as a method of inbreeding
• Humans choosing phenotypes in selective breeding (artificial selection)

Genetic Drift

• Changes in the genetic makeup of a population (alleles that are passed on to another generation) resulting from chance
  • In small populations, chance can play a role in altering allele frequencies and population makeup

Key Events that lead to Genetic Drift

Founder Effect

• When new populations form as only a few individuals relocate
  • Allele frequencies of the new population will not be the same as the original population
  • Lack of genetic diversity can be a concern

Bottleneck Effect

• Due to artificial or natural selective pressures, a large population at times could be drastically diminished

Natural Selection

• The existing environment can change an existing population through 4 modes

Stabilizing Selection

• The most common phenotypes are favoured by the environment

Directional Selection

• The environment favours individuals of one extreme for a trait

Disruptive Selection

• The environment favours individuals of both extremes for a trait

Sexual Selection

• This happens when Males forcefully compete for a mate
• Sexual Dimorphism - Males and females demonstrate phenotypic differences

Summarizing Chart (pls share my website)

References

5.0 Intro to Evolution
5.2 Scientific Contributions to the Theory of Evolution
5.3 Evidence of Evolution
5.5 Speciation