Cell Cycle / Mitosis-Meiosis Viewer

Mitosis is the type of cell division that produces two genetically identical daughter cells from a single parent cell. It is used for growth, repair, and asexual reproduction.

Phases in order

1. Interphase - DNA replicates (S phase); cell grows (G1 and G2 phases)
2. Prophase - Chromatin condenses into visible chromosomes; spindle begins to form
3. Metaphase - Chromosomes align at the metaphase plate; spindle fibers attach to kinetochores
4. Anaphase - Sister chromatids separate and move to opposite poles
5. Telophase - Nuclear envelopes reform; chromosomes decondense
6. Cytokinesis - Cytoplasm divides, producing two daughter cells

Each daughter cell receives a complete copy of the genome and has the same chromosome number as the parent cell (2n).

Meiosis involves two sequential divisions (meiosis I and meiosis II) that produce four haploid (n) daughter cells from one diploid (2n) parent cell. It is essential for sexual reproduction.

Key differences from mitosis

• Meiosis I separates homologous chromosomes (reductional division). The chromosome number is halved from 2n to n.
• Meiosis II separates sister chromatids (equational division), similar to mitosis but in haploid cells.
• The result is 4 genetically unique haploid cells (gametes).

There is no DNA replication between meiosis I and meiosis II.

Two main mechanisms during meiosis generate genetic diversity.

Crossing over occurs during prophase I when homologous chromosomes exchange segments of DNA at points called chiasmata. This creates new allele combinations on each chromatid.

Independent assortment occurs at metaphase I when homologous pairs orient randomly at the metaphase plate. With n chromosome pairs, there are

For humans with 23 pairs, that gives $2^{23} = 8{,}388{,}608$ unique combinations before even accounting for crossing over. When two gametes fuse during fertilization, the possible zygote combinations are $(2^{23})^2 \approx 70 \text{ trillion}$.

Both types of division begin with DNA replication in S phase. The critical difference is that meiosis I separates homologous chromosomes while mitosis (and meiosis II) separates sister chromatids.