Meiosis: Understanding Cell Division and Genetic Diversity
Meiosis involves two consecutive cell divisions, resulting in four haploid cells per diploid mother cell. These divisions occur in prophase, metaphase, anaphase, and telophase.
Meiotic Division 1
The fundamental difference between meiosis and mitosis takes place in prophase. Homologous chromosomes pair up and exchange hereditary material.
Prophase 1
- DNA filaments begin to condense, chromosomes become visible, and each chromosome is replicated into two chromatids.
- Homologous chromosomes pair lengthwise (with their counterparts), this is called synapsis.
- Two adjacent homologous chromatids are intimately joined at some points, forming chiasmata.
- Crossover occurs, producing chromosomes with genetic recombination of hereditary material.
Metaphase 1
Pairs of homologous chromosomes migrate to the equatorial plane of the spindle, giving rise to the double metaphase plate.
Anaphase 1
Homologous chromosomes are separated, each moving to a distinct cell pole.
Telophase 1
The nuclei of the two daughter cells are formed.
Meiotic Division 2
This division starts after a brief interphase in which DNA does not double, similar to mitosis.
Prophase 2
Chromosomes condense again.
Metaphase 2
Chromosomes align in the equatorial plane.
Anaphase 2
Sister chromatids are separated from each chromosome.
Telophase 2
The nuclei of the daughter cells are reconstructed.
Consequences of Meiosis
- In the interphase after the first meiotic division, the chromosomes of the diploid mother cell are replicated, forming two pairs of homologous chromatids. These are divided into two haploid daughter cells.
- In the interphase prior to the second division, there is no synthesis period. During the second division, both chromatids of a chromosome are divided into two daughter cells.
- The end result is four haploid cells produced by meiosis.
- The nuclei contain a new combination of genes resulting from recombination.
- The result is an increase in genetic variability.