Overview
This lecture explains the process of meiosis, its stages, and its importance in sexual reproduction, highlighting differences from mitosis and key terminology.
Introduction to Meiosis
- Meiosis is a type of cell division that reduces chromosome number by half, producing four haploid cells.
- It occurs only in gametes (sperm and egg cells) for sexual reproduction.
- Meiosis helps maintain chromosome number across generations.
Phases of Meiosis
- Meiosis has two main stages: Meiosis I and Meiosis II.
- Each stage includes prophase, metaphase, anaphase, and telophase.
Meiosis I: Reduction Division
- Prophase I: Homologous chromosomes pair up (synapsis) and exchange genetic material (crossing over).
- Metaphase I: Paired homologous chromosomes align at the cell equator.
- Anaphase I: Homologous pairs separate to opposite poles.
- Telophase I: Two haploid cells form, each with half the original chromosome number.
Meiosis II: Division of Sister Chromatids
- Prophase II: Chromosomes condense in two haploid cells.
- Metaphase II: Chromosomes align at the equator in each cell.
- Anaphase II: Sister chromatids are pulled apart.
- Telophase II: Four haploid daughter cells are formed.
Importance and Consequences of Meiosis
- Produces genetic diversity through crossing over and independent assortment.
- Ensures offspring have the same chromosome number as parents.
- Accounts for variation seen in sexually reproducing organisms.
Comparison with Mitosis
- Meiosis results in four genetically unique haploid cells, while mitosis yields two identical diploid cells.
- Meiosis involves two divisions; mitosis only one.
Key Terms & Definitions
- Meiosis — Cell division reducing chromosome number by half to form gametes.
- Haploid — Cell with one set of chromosomes (n).
- Diploid — Cell with two sets of chromosomes (2n).
- Homologous Chromosomes — Pair of chromosomes with the same genes but possibly different alleles.
- Crossing Over — Exchange of genetic material between homologous chromosomes during prophase I.
- Gametes — Reproductive cells (sperm and egg).
Action Items / Next Steps
- Review diagrams illustrating the stages of meiosis.
- Complete assigned reading on meiosis vs. mitosis.
- Prepare for quiz on meiosis terminology and stages.