Understanding Meiosis and Genetic Diversity

Key Concepts

• Meiosis is the process that generates gametes for reproduction.
• It produces haploid cells from a diploid cell.
• Important for genetic diversity in offspring.

Meiosis Process Overview

• Location: Occurs in germ cells within the gonads of males and females.
• Divisions: Two rounds - Meiosis I and Meiosis II.
• End Result: Meiosis results in four haploid cells (gametes).

Differences Between Mitosis and Meiosis

• Mitosis: Produces 2 diploid daughter cells.
• Meiosis: Produces 4 haploid daughter cells.
• Both begin after G1, S, and G2 stages of interphase.

Stages of Meiosis

Meiosis I

1. Prophase I:
   • Homologous pairs of sister chromatids lie side by side (synapsis).
   • Formation of tetrad (bivalent).
   • Crossing over occurs, increasing genetic diversity.
2. Metaphase I:
   • Tetrads align randomly along metaphase plate (independent assortment).
3. Anaphase I:
   • Homologous chromosomes separate.
4. Telophase I:
   • Chromosomes de-condense, nuclear envelope reforms.
   • Cytokinesis separates two daughter cells.

Meiosis II

1. Prophase II:
   • Sister chromatids condense; spindle forms.
2. Metaphase II:
   • Sister chromatids aligned along the metaphase plate.
3. Anaphase II:
   • Sister chromatids separate and move to poles.
4. Telophase II:
   • Chromosomes de-condense, nuclear envelope reforms.
   • Cytokinesis separates the cells into four haploid daughter cells.

Genetic Diversity Mechanisms

• Crossing Over: Exchange of DNA between non-sister chromatids during prophase I.
• Independent Assortment: Random alignment of homologous chromosomes during metaphase I.
• Results in increased genetic combinations:
  • Formula: 2^n (where n = number of chromosome pairs).
  • In humans (n = 23): 2^23 = over 1 million combinations.

Conclusion

• The combination of crossing over and independent assortment leads to genetic diversity.
• Explains why children do not look exactly like their parents and why siblings may look different.