22 Biology -- Cell Division

Describe Meiosis with well labelled diagram.

Describe Meiosis with well labelled diagram.

Meiosis is a complex cellular process that occurs in sexually reproducing organisms to produce haploid cells, such as gametes (sperm and eggs). It involves two rounds of cell division, known as meiosis I and meiosis II, resulting in the production of four genetically unique daughter cells.

Here is a step-by-step description of the process of meiosis:

1. Interphase: The cell undergoes a period of growth and prepares for division. During this phase, the DNA replicates, ensuring that each chromosome consists of two identical sister chromatids.

2. Prophase I: This is the longest and most complex phase of meiosis. Chromatin condenses into visible chromosomes, and homologous chromosomes pair up to form tetrads. Within tetrads, a process called crossing over occurs, where genetic material is exchanged between non-sister chromatids of homologous chromosomes. This genetic recombination increases genetic variation. The nuclear envelope begins to break down, and spindle fibers start to form.

3. Metaphase I: The tetrads line up along the cell's equator, or the metaphase plate, through the attachment of spindle fibers to the centromeres of each chromosome.

4. Anaphase I: Homologous chromosomes separate and are pulled towards opposite poles of the cell by the shortening of spindle fibers. Sister chromatids remain attached at their centromeres.

5. Telophase I: The separated homologous chromosomes arrive at opposite poles, and the spindle fibers disassemble. The nuclear envelope may briefly reform, and the cell undergoes cytokinesis, dividing into two daughter cells.

6. Interphase II: The two daughter cells produced from meiosis I may enter a brief interphase II, where DNA replication does not occur.

7. Prophase II: The nuclear envelope breaks down, and new spindle fibers start forming in each daughter cell.

8. Metaphase II: Chromosomes, consisting of two sister chromatids, line up along the metaphase plate in each daughter cell.

9. Anaphase II: The sister chromatids separate and are pulled towards opposite poles of the cell.

10. Telophase II: The separated sister chromatids arrive at opposite poles, and nuclear envelopes start to form around each set of chromosomes.

11. Cytokinesis: The cell divides into four haploid daughter cells. Each daughter cell contains only one set of chromosomes (half the number of chromosomes found in the parent cell). These cells are genetically distinct due to crossing over during prophase I and the random assortment of chromosomes during metaphase I.

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