BSC2010-evolution-5-2024

Microevolution Causes

Main Factors

  • Mutation: Changes in nucleotide sequences that can introduce new alleles; includes point mutations and gene duplications.

  • Gene Flow: Movement of alleles between populations, reducing differences.

  • Genetic Drift: Random events affecting allele frequencies.

  • Nonrandom Mating: Includes sexual recombination.

  • Natural Selection: Differential reproductive success that shapes organisms.

Mutation Details

Definition and Significance Mutation is a change in the nucleotide sequence of DNA that can be passed through generations.

Types of Mutations:

  • Point Mutations: Small changes in DNA sequences.

  • Gene Duplications: Copying of DNA segments.

Frequency: Generally low, but vital as the source of genetic variation.

Causes of Mutation

  • DNA Replication Mistakes: Errors during cell division.

  • Chemical and Physical Mutagens: These include radiation and various chemicals that damage DNA.

  • Viruses: Can insert their genetic material into host DNA, causing mutations.

Gene Flow

Overview Describes the genetic exchange that occurs via immigration and emigration among populations. Tends to minimize genetic differences by reducing variance in allele frequencies.

Genetic Drift

Definition Refers to chance events that alter allele frequencies in populations, often leading to decreased genetic variation.

Effects of Genetic Drift:

  • Bottleneck Effect: Occurs when a significant reduction in population size leads to loss of genetic diversity.

  • Founder Effect: Establishment of a new population by a small number of individuals, resulting in a limited gene pool.

Populations and Genetic Drift Population Size Impact

  • The formula for variance in allele frequency is: Variance (p) = pq/2N N is the population size; smaller populations are more susceptible to genetic drift.

Examples of Genetic Drift Founder Effect Example

  • The Afrikaner Population in South Africa, descendants of a small group of Dutch settlers, exhibits a notable frequency of Huntington’s disease due to the founder effect from the limited genetic diversity of early settlers.

Natural Selection

Role in Evolution Natural selection is the process that leads to adaptations, impacting the reproductive success of organisms.

Types of Selection:

  • Stabilizing Selection: Favors average individuals.

  • Directional Selection: Favors individuals at one extreme.

  • Disruptive Selection: Favors individuals at both extremes.

Example of Natural Selection

  • Pesticide Resistance in Insects: Pesticides eliminate susceptible individuals, increasing susceptibility to insect resistance over generations, demonstrating natural selection.

Fitness and Adaptation

Definitions

  • Fitness: The relative contribution an individual makes to the gene pool of the next generation.

  • Adaptation: Traits developed through natural selection that enhance fitness.

Importance of Adaptation Adaptations are essential for survival and reproduction, allowing species to thrive in their environments.