Meiosis and Genetic Diversity

Study Notes

Meiosis is a type of cell division, specifically a reduction division.
Meiosis occurs in germ cells (gametes).
It produces four daughter cells with half the number of chromosomes of the parent cell.
This process is crucial for sexual reproduction, ensuring genetic diversity across generations.
Meiosis differs from mitosis through two rounds of division, leading to four genetically diverse haploid nuclei.

Gametic: Meiosis occurs directly before gamete formation in animals.
Sporic: Meiosis occurs in the sporophyte phase of some plants and algae.
Zygotic: Meiosis occurs immediately after fertilization in some protists and fungi.

Spermatogenesis: The process of sperm cell formation. One cell produces four sperm cells.
Oogenesis: The process of egg production. One cell produces one egg and three polar bodies.

Prophase I: Homologous chromosomes pair up, forming tetrads; crossing over occurs.
Synapsis and crossing over occur between non-sister chromatids.
Metaphase I: Homologous pairs align along the metaphase plate.
Anaphase I: Homologous chromosomes separate.
Telophase I and Cytokinesis: Chromosomes arrive at the poles, two daughter cells are formed, each with half the original number of chromosomes.
Prophase II, Metaphase II, Anaphase II and Telophase/Cytokinesis II: Sister chromatids separate, forming four genetically unique haploid cells.

Crossing over: Exchange of genetic material between non-sister chromatids of homologous chromosomes.
Independent assortment: Random alignment of homologous pairs during metaphase I.
Random fertilization: Combination of different gametes during fertilization.

Nondisjunction: Failure of homologous chromosomes or sister chromatids to separate correctly during meiosis, leading to aneuploidy (e.g., Down Syndrome).