Meiosis Overview and Stages

Meiosis

• Meiosis is a specialized type of cell division that produces four genetically unique haploid daughter cells from a single diploid parent cell. This process is essential for sexual reproduction.
• It involves two rounds of division: meiosis I and meiosis II.
• Meiosis is crucial for maintaining a consistent chromosome number across generations in sexually reproducing organisms.

Stages of Meiosis

• Meiosis I

• Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis), crossing over occurs (exchange of genetic material) between non-sister chromatids.

• Metaphase I: Homologous chromosome pairs align at the metaphase plate. Independent assortment of homologous chromosomes occurs.

• Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell. Sister chromatids remain attached.

• Telophase I and Cytokinesis: Chromosomes arrive at the poles, the cytoplasm divides, producing two haploid daughter cells. Chromosomes may or may not decondense.

• Meiosis II

• Prophase II: Chromosomes condense if they decondensed. Spindle fibers form.

• Metaphase II: Sister chromatids align at the metaphase plate.

• Anaphase II: Sister chromatids separate and move to opposite poles.

• Telophase II and Cytokinesis: Sister chromatids arrive at the poles, the cytoplasm divides, producing four haploid daughter cells.

Meiosis vs. Mitosis

• Mitosis produces two genetically identical diploid daughter cells from a single diploid parent cell. It is used for growth, repair, and asexual reproduction.
• Meiosis produces four genetically unique haploid daughter cells from a single diploid parent cell, used for sexual reproduction.
• Key differences:
• Number of divisions: Mitosis has one division; meiosis has two.
• Genetic variation: Mitosis produces identical cells; meiosis produces genetically unique cells.
• Chromosome number: Mitosis maintains the same chromosome number; meiosis reduces the chromosome number by half.

Genetic Variation

• Meiosis contributes significantly to genetic variation through several mechanisms:
• Crossing over (Prophase I): Exchange of genetic material between homologous chromosomes, creating new combinations of alleles.
• Independent assortment (Metaphase I): Random alignment of homologous chromosome pairs, leading to different combinations of maternal and paternal chromosomes in daughter cells.
• Random fertilization: The fusion of gametes from two different individuals, further increasing genetic diversity.
• Combined, these processes lead to a vast range of genetic variations in offspring.