General Overview of Meiosis
- Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction, and during reproduction, when the sperm and egg unite to form a single cell, the number of chromosomes is restored in the offspring.
Meiosis 1--Meiosis 2
- Meiosis is somewhat a long and far-ranging process of cellular reproduction in gamete cells, and this biological process is divided into Meiosis 1 and Meiosis 2. Meiosis 1 is when one diploid nucleus divides to two haploid nuclei, and Meiosis 2 is when two haploid nuclei divide to four haploid nuclei.
- During Prophase 1, homologous chromosomes condense, pair up, and swap segments. Spindle microtubules attach to them as the nuclear envelope breaks up and disappears. Prophase 1 is also the longest phase of meiosis.
- During Metaphase 1, the homologous chromosome pairs are aligned between spindle poles. Spindle microtubules attach the two chromosomes of each pair to opposite spindle poles.
- During Anaphase 1, all of the homologous chromosomes separate and begin heading toward the spindle poles at opposite sides of the cell.
- During Telophase 1, a complete set of chromosomes clusters at both ends of the cell. A nuclear envelope, which disappeared during Prophase 1, forms around each set, so two haploid (n=23) nuclei form.
- During Prophase II, the chromosomes condense. Spindle microtubules attach to each sister chromatid as the nuclear envelope breaks up and disappears.
- During Metaphase II, the (still duplicated) chromosomes are aligned midway between the spindle poles. At this stage of Meiosis 2, the chromosomes don't move to the sides of the spindles.
- During Anaphase II, the sister chromatids separate. The now unduplicated chromosomes head to the spindle poles on each opposite side of the cell.
- During Telophase II, a complete set of chromosomes clusters at both ends of the cell. A new nuclear envelope forms around each set, so four haploid (n=23) nuclei form.
Meiosis 1 and Meiosis 2 are only possible if sperm and egg fertilization occur in eukaryotic organisms.