Mitosis and Meiosis by Yazmeen A. D'Ottavi

ydottavi — 2025-02-05 17:33:37 UTC

The key steps of mitosis are:

Prophase: Chromosomes condense and become visible. The nuclear envelope begins to break down, and the mitotic spindle begins to form from the centrosomes.
Metaphase: The chromosomes line up at the cell's equator (the metaphase plate) and attach to the spindle fibers through their centromeres.
Anaphase: The sister chromatids are pulled apart toward opposite poles of the cell as the spindle fibers shorten.
Telophase: The chromatids reach the poles and start to de-condense into chromatin. The nuclear envelope re-forms around each set of chromosomes.
Cytokinesis: The cytoplasm divides, resulting in two daughter cells, each with an identical set of chromosomes.

The daughter cells are genetically identical to each other and the parent cell, each with a full set of chromosomes (diploid).

ydottavi — 2025-02-05 17:34:04 UTC

Purpose: Meiosis is for sexual reproduction, producing four genetically unique daughter cells (gametes like sperm or eggs), each with half the chromosome number (haploid).
Key Differences in Meiosis:
- Meiosis I (Reduction Division):
  - Prophase I: Homologous chromosomes pair up and undergo crossing-over, exchanging genetic material, which increases genetic variation.
  - Metaphase I: Homologous chromosomes align randomly at the equator (independent assortment), further contributing to genetic diversity.
  - Anaphase I: Homologous chromosomes are separated, not sister chromatids.
  - Telophase I: Two haploid cells form.
- Meiosis II (Similar to Mitosis):
  - Prophase II, Metaphase II, Anaphase II, Telophase II: The two haploid cells divide again without DNA replication, separating the sister chromatids into four unique haploid cells.
The four resulting daughter cells are genetically unique due to crossing-over and independent assortment, and each has only half the DNA (haploid).

ydottavi — 2025-02-05 17:35:24 UTC

During meiosis, crossing-over and independent assortment generate genetic variation.

Crossing-over occurs in Prophase I, where homologous chromosomes exchange genetic material, creating new combinations of alleles.
Independent assortment happens in Metaphase I, where chromosomes line up randomly, ensuring that different combinations of alleles are passed on to offspring.

Mendel's Law of Independent Assortment states that genes for different traits are inherited independently because chromosome pairs sort randomly during meiosis, creating genetic diversity.