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Understanding Meiosis and Genetic Diversity

May 27, 2025

Lecture on Meiosis

Introduction

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  • Topic: Why siblings with the same parents can look different.
  • Main concept: Meiosis, not to be confused with mitosis.

Mitosis vs. Meiosis

  • Mitosis:

    • Creates identical body cells (e.g., skin, stomach cells).
    • Important for growth, repair, and replacing worn out cells.
  • Meiosis:

    • Contributes to genetic variety.
    • Produces gametes (sperm and egg cells).
    • Human body cells have 46 chromosomes; sperm and egg cells have 23.
    • Reduction division: starting cell (46 chromosomes) -> ending cells (23 chromosomes each).

Pre-Meiosis: Interphase

  • Occurs before meiosis (and mitosis).
  • Cell growth, DNA replication, carries out cell processes.
  • Chromosomes duplicate (46 chromosomes -> 92 chromatids).
  • Chromosome count based on centromeres remains 46.

Meiosis Process

  • Divides twice (PMAT phases performed twice):
    • PMAT: Prophase, Metaphase, Anaphase, Telophase.

Meiosis I

  • Prophase I:

    • Chromosomes condense and line up in homologous pairs.
    • Crossing over occurs, exchanging genetic information.
    • Result: recombinant chromosomes, contributing to genetic variety.
  • Metaphase I:

    • Chromosomes align in the middle, in homologous pairs.
  • Anaphase I:

    • Homologous chromosomes pulled away by spindle fibers.
  • Telophase I:

    • Two new nuclei form, cytokinesis follows.
    • Results in two new cells.

Meiosis II

  • Prophase II:

    • Chromosomes, not in homologous pairs.
    • No crossing over.
  • Metaphase II:

    • Chromosomes align in a single file line in the middle.
  • Anaphase II:

    • Chromatids pulled away by spindle fibers to opposite sides.
  • Telophase II:

    • Nuclei reform, results in four new cells after cytokinesis.

Outcomes of Meiosis

  • Produces gametes:
    • Males: 4 diverse sperm cells.
    • Females: 4 diverse egg cells.
  • Each gamete is unique due to independent assortment and crossing over.
  • Explains genetic diversity among siblings.

Scientific Study

  • Nondisjunction:
    • Failure of chromosomes to separate correctly.
    • Can lead to genetic disorders.

Conclusion

  • Encouragement to "stay curious."