Meiosis Produces Four Haploid Nuclei from One Diploid Nucleus
Definition
Meiosis
Meiosis is a type of cell division that reduces the chromosome number by half, producing four genetically distinct haploid cells. This process occurs in gamete-producing cells and is essential for sexual reproduction.
- Diploid cells contain two complete sets of chromosomes (one from each parent).
- Haploid cells contain one complete set of chromosomes.
- This reduction prevents chromosome doubling when gametes fuse during fertilization.
- There are two stages to meiosis.
Meiosis I: Reduction Division
Meiosis I separates homologous chromosomes, pairs of chromosomes with the same genes in the same order but potentially different alleles.
- Prophase I:
- Homologous chromosomes pair up during synapsis, forming structures called bivalents.
- Crossing over occurs when non-sister chromatids exchange genetic material, creating new allele combinations.
- Metaphase I:
- Bivalents align at the cell's equator.
- Each bivalent's orientation is random—a process called independent assortment that increases genetic diversity.
- In humans with 23 chromosome pairs, independent assortment alone can produce over 8 million possible combinations (2²³).
- Anaphase I:
