Cell Division: Mitosis and Meiosis
Grade 10 · Science · Study Guide
Understand how cells reproduce through mitosis (for growth and repair) and meiosis (for sexual reproduction).
All living things grow, develop, and reproduce at the cellular level through cell division. There are two main types of cell division: mitosis and meiosis, each serving a different biological purpose. Before either process begins, the cell must copy its DNA during S phase (DNA synthesis) of the cell cycle, so each daughter cell receives a complete genome.
Mitosis produces two genetically identical daughter cells from one parent cell. It consists of four phases: prophase (chromosomes condense, spindle forms), metaphase (chromosomes align at the cell's equator), anaphase (sister chromatids are pulled to opposite poles), and telophase (nuclear envelopes reform). Mitosis is used for growth, tissue repair, and asexual reproduction. The result: 2 diploid (2n) cells identical to the parent.
Meiosis produces four genetically unique haploid (n) daughter cells for sexual reproduction (gametes: sperm and eggs). It involves two rounds of division: Meiosis I separates homologous chromosomes (after crossing over, which shuffles genetic material), and Meiosis II separates sister chromatids. The result is 4 cells each with half the original chromosome number. When egg and sperm fuse at fertilization, the diploid number is restored. Meiosis generates genetic diversity through crossing over and independent assortment — critical for evolution.
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, repair, asexual reproduction | Sexual reproduction (gamete formation) |
| Divisions | 1 | 2 (Meiosis I and II) |
| Daughter cells | 2 | 4 |
| Ploidy of daughters | Diploid (2n) | Haploid (n) |
| Genetic identity | Identical to parent | Genetically unique |
| Crossing over occurs? | No | Yes (Meiosis I) |
Key terms
- Mitosis
- Cell division producing two genetically identical diploid daughter cells; used for growth and repair.
- Meiosis
- Cell division producing four genetically unique haploid cells (gametes); used for sexual reproduction.
- Diploid (2n)
- Having two complete sets of chromosomes (one from each parent); normal body cells are diploid.
- Haploid (n)
- Having one set of chromosomes; gametes (sperm and eggs) are haploid.
- Crossing over
- Exchange of genetic segments between homologous chromosomes during Meiosis I; increases genetic diversity.
- Sister chromatids
- Two identical copies of a chromosome joined at the centromere after DNA replication.
Flashcards
- Cell cycle
- The ordered series of events a cell goes through to grow and divide: G1, S (DNA replication), G2, and M (mitosis/cytokinesis).
- Chromosome
- Condensed structure of DNA and proteins; humans have 46 chromosomes (23 pairs) in body cells.
- Homologous chromosomes
- Matching chromosome pairs (one from each parent) with the same genes at the same locations.
- Prophase
- First phase of mitosis/meiosis: chromosomes condense and become visible; spindle fibers form.
- Metaphase
- Phase where chromosomes align along the metaphase plate (cell's equator) before being separated.
- Anaphase
- Phase where sister chromatids (or homologous chromosomes in Meiosis I) are pulled to opposite poles.
Practice questions
Which type of cell division results in genetically unique haploid cells?
- Mitosis
- Binary fission
- Meiosis
- Cytokinesis
Show answer
Answer: Meiosis
Meiosis produces four haploid (n) cells with genetic variation due to crossing over and independent assortment — these become gametes for sexual reproduction.
Cells produced by mitosis are genetically identical to the parent cell.
Show answer
Answer: True
Mitosis produces daughter cells that are genetically identical copies of the parent cell because no genetic mixing occurs — the copied chromosomes are simply separated.
The exchange of chromosome segments between homologous chromosomes during meiosis is called crossing ___.
Show answer
Answer: over
Crossing over occurs during prophase I of meiosis when homologous chromosomes pair up and exchange segments of DNA, generating new combinations of alleles.
During which phase of mitosis do chromosomes line up along the cell's equator?
- Prophase
- Metaphase
- Anaphase
- Telophase
Show answer
Answer: Metaphase
During metaphase, spindle fibers attach to chromosomes at the centromere and align them at the cell's middle (metaphase plate) before separation in anaphase.
Human gametes (sperm and eggs) are diploid cells.
Show answer
Answer: False
Human gametes are haploid (n=23) — they contain only one set of chromosomes. When sperm (n) and egg (n) fuse during fertilization, the resulting zygote is diploid (2n=46).
Fun facts
- Your body replaces about 3.8 million cells every single second — most through mitosis.
- During crossing over in meiosis, chromosomes literally swap segments of DNA, meaning your gametes are never exact copies of your own chromosomes.
- Cancer is essentially uncontrolled mitosis — cells divide without responding to normal stop signals.
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