Genetic Variation and Natural Selection Notes

Changes in Genotype and Phenotype

  • Genotype-Phenotype Relationship
    • Changes in genotype can lead to observable changes in phenotype, which may be affected by natural selection.
    • Natural selection favors traits that enhance survival and reproduction, allowing these traits to be passed on to the next generation.

Natural Selection

  • Process
    • Organisms that are better adapted to their environment are more likely to survive and reproduce.
  • Outcome
    • Genetic changes that provide advantages can be selected for by environmental factors, enhancing adaptation.

Horizontal Acquisition of Genetic Information

  • Definition
    • Refers to the transfer of genetic information between different genomes or unrelated organisms.
  • Importance
    • This process increases genetic variation and is particularly significant in prokaryotic organisms where it occurs primarily.
Mechanisms of Horizontal Gene Transfer in Prokaryotes

  • Transformation

    • Uptake of naked DNA from the environment by a prokaryotic cell.
    • Naked DNA: DNA not protected by proteins, sourced externally.

  • Transduction

    • Involves the transfer of foreign DNA into a cell via a virus.
    • Virus integrates its genome with the host genome, introducing new genetic material into the bacterial cell.

  • Conjugation

    • DNA transfer between bacterial cells through direct contact, facilitated by an external connection (pilus).
    • Allows for transfer of small segments of DNA.

  • Transposition

    • Movement of DNA segments within and between DNA molecules.
    • Can involve deletion, duplication, or inversion of DNA pieces.
    • Example: Combined genetic information from multiple viruses infecting the same cell can produce new viral combinations.

Reproductive Processes Increasing Genetic Variation

  • Sexual Reproduction

    • Combines random gametes, creating diverse offspring due to variable combinations of genetic material.
    • Unpredictability of which sperm will fertilize which egg leads to new traits.

  • Independent Assortment

    • During meiosis, chromosomes inherit independently, resulting in increased genetic combinations due to random line-up.

  • Crossing Over

    • During meiosis, segments of homologous chromosomes are exchanged, producing new combinations of genes.
    • Example: Combination of alleles such as big A and little b, creating genetic variation.

Key Takeaways

  • Genetic changes that enhance survival and reproduction can be selected based on environmental conditions.
  • Horizontal acquisition includes:
    • Transfer of DNA segments between cells and viruses to cells, and movement of DNA within and between segments.
  • Sexual reproduction, independent assortment of chromosomes, and crossing over all contribute to increased genetic variation.