Mitosis and Meiosis Overview

Mitosis

• Mitosis is a type of cell division that produces two genetically identical diploid daughter cells from a single diploid parent cell.
• It is crucial for growth, repair, and asexual reproduction in many organisms.
• The process involves several distinct phases:
  • Interphase: The cell grows, replicates its DNA, and prepares for division.
  • Prophase: Chromosomes condense and become visible, the nuclear envelope breaks down, and the mitotic spindle begins to form.
  • Metaphase: Chromosomes align along the metaphase plate (equator of the cell).
  • Anaphase: Sister chromatids separate and move to opposite poles of the cell.
  • Telophase: Chromosomes decondense, the nuclear envelope reforms, and the cell begins to divide.
  • Cytokinesis: The cytoplasm divides, resulting in two daughter cells.
• Mitosis ensures that each daughter cell receives a complete and identical set of chromosomes.

Meiosis

• Meiosis is a specialized type of cell division that produces four genetically unique haploid daughter cells from a single diploid parent cell.
• It is essential for sexual reproduction, generating gametes (sperm and eggs) with half the number of chromosomes compared to the parent cell.
• Meiosis involves two rounds of division:
  • Meiosis I: Homologous chromosomes separate, reducing the chromosome number by half. Includes prophase I (crossing over), metaphase I, anaphase I, and telophase I.
  • Meiosis II: Sister chromatids separate, similar to mitosis. Includes prophase II, metaphase II, anaphase II, and telophase II.
• Crossing over during prophase I is a key mechanism for genetic variation. It involves the exchange of genetic material between homologous chromosomes.
• Meiosis results in genetic diversity among the gametes, contributing to genetic variation in offspring.

Chromosomal Abnormalities

• Chromosomal abnormalities occur when there are alterations in the number or structure of chromosomes.
• These abnormalities can arise during meiosis or mitosis, potentially leading to various health problems.
• Numerical abnormalities:
  • Aneuploidy: An abnormal number of chromosomes, such as monosomy (one copy) or trisomy (three copies).
    • Down syndrome (trisomy 21) is an example of aneuploidy.
  • Polyploidy: Multiple sets of chromosomes; common in plants, less frequent in animals.
• Structural abnormalities:
  • Deletions: Loss of a portion of a chromosome.
  • Duplications: Presence of a repeated segment on a chromosome.
  • Inversions: A segment of a chromosome is reversed.
  • Translocations: A segment of one chromosome breaks off and attaches to another.
• Consequences of chromosomal abnormalities can vary greatly, ranging from no observable effects to severe developmental disorders, such as intellectual disabilities, physical malformations, and increased risks of genetic diseases.
• Factors that can increase the risk of chromosomal abnormalities include advanced parental age and exposure to mutagens (e.g., radiation).
• Genetic testing can detect chromosomal abnormalities in individuals or embryos, aiding in diagnosis and management of the condition.
• Diagnosis and management of chromosomal abnormalities often involve clinical genetic counseling to support individuals and families.