Meiosis Bio1090

Overview of Cell Division

  • Mitosis: Results in two genetically identical daughter cells, maintaining DNA amount and type.

  • Meiosis: Results in four genetically unique daughter cells, reducing DNA type and amount.

Key Terms

  • Ploidy: Refers to the number of complete sets of chromosomes in a cell.

    • Haploid (N): One set of chromosomes (23 in humans, e.g., sperm and egg cells).

    • Diploid (2N): Two sets of chromosomes (46 in humans, e.g., somatic cells).

    • Tetraploid: Four sets of chromosomes, seen in some plants.

Differences Between Mitosis and Meiosis

  • Mitosis:

    • 1 Division cycle (G1, S, G2, M).

    • Results in 2 identical diploid daughter cells.

    • DNA amount doubles, ploidy level remains 2N.

  • Meiosis:

    • 2 Division cycles (Meiosis I and II).

    • Results in 4 unique haploid daughter cells.

    • First division separates homologous chromosomes; second separates sister chromatids.

    • Ploidy changes from 2N to N after the first division.

Stages of Meiosis

Meiosis I

  • Prophase I: Chromosomes condense, homologous chromosomes pair (synapsis) forming bivalents. Crossing over occurs at chiasma.

  • Metaphase I: Homologous pairs align at the center of the cell.

  • Anaphase I: Homologous chromosomes separate, sister chromatids remain together.

  • Telophase I: Two daughter cells form, each with half the chromosome number but still doubled DNA.

Meiosis II

  • Prophase II: Chromosomes condense, nuclear envelope breaks down.

  • Metaphase II: Sister chromatids align at the center.

  • Anaphase II: Sister chromatids separate.

  • Telophase II: Four genetically unique haploid daughter cells form.

Genetic Diversity

  • Meiosis increases genetic diversity through crossing over and independent assortment:

    • Crossing over in Prophase I mixes maternal and paternal DNA.

    • Independent assortment during Metaphase I leads to varied combinations of chromosomes.

Gender Differences in Meiosis

  • Males: Continuous sperm production through meiosis resulting in four haploid sperm.

  • Females: Egg production is limited; meiosis occurs only to finalize egg release, resulting in one functional egg and three polar bodies.

Conclusion

  • Mitosis and meiosis serve different roles in growth, repair, and reproduction.

  • Understanding these processes is crucial in genetics and developmental biology.