Overview
This lecture provides a high-level comparison between mitosis and meiosis, focusing on chromosome numbers, outcomes, and where these processes occur in the body.
Mitosis Overview
- Mitosis starts with a diploid cell (2n), which for humans is 46 chromosomes.
- 23 chromosomes come from the mother, and 23 from the father, forming homologous pairs.
- After mitosis and cytokinesis, two genetically identical diploid cells are produced.
- Each resulting cell can repeat the cell cycle, allowing for growth and repair in somatic (body) cells.
- Mitosis is a continuous cycle.
Meiosis Overview
- Meiosis also begins with a diploid cell (2n) that replicates its DNA during interphase.
- Meiosis has two main phases: Meiosis I and Meiosis II.
- After Meiosis I, two cells with a haploid number (n) of chromosomes (23 in humans) are formed.
- Homologous chromosome pairs are split randomly during Meiosis I, causing genetic variation.
- Each haploid cell divides again in Meiosis II, resulting in four haploid gametes.
- The four gametes are not genetically identical due to the random assortment of homologous chromosomes.
Functional Differences
- Mitosis produces identical somatic cells for growth and repair.
- Meiosis produces gametes (sperm or egg cells), which are used for sexual reproduction.
- Meiosis is not a cycle; gametes fuse during fertilization to form a new organism.
Cellular Locations
- Mitosis occurs in somatic cells, which make up most of the body.
- Meiosis occurs in germ cells: testes for males (sperm), ovaries for females (egg cells).
- Germ cells can either undergo mitosis to produce more germ cells or meiosis to produce gametes.
Key Terms & Definitions
- Diploid (2n) — A cell with two sets of chromosomes (homologous pairs), such as most human cells.
- Haploid (n) — A cell with one set of chromosomes, such as gametes.
- Homologous pairs — Chromosome pairs, one from each parent, similar in size and gene content.
- Somatic cells — Body cells not involved in reproduction.
- Germ cells — Cells in reproductive organs that can become gametes through meiosis.
- Gametes — Reproductive cells (sperm or egg) with a haploid set of chromosomes.
- Meiosis — Two-part cell division process producing four genetically unique, haploid cells from one diploid cell.
- Mitosis — Cell division process resulting in two identical diploid daughter cells.
Action Items / Next Steps
- Review the stages of Meiosis I and II in detail in upcoming lessons or assigned readings.