Meiosis and Mitosis: Chromosomal Separation

Key Concepts

• Chromosomal Separation: Involves the separation and migration of homologous chromosomes and chromatids during cell division.
• Mitosis: Responsible for producing haploid cells from original diploid cells.

Meiosis

Phases of Meiosis

• First Round:
  • Homologous chromosomes separate.
  • Migration to opposite poles during anaphase.
• Second Round:
  • Chromatids separate and move to opposite poles.

Nondisjunction

• Occurs when chromosomes fail to separate properly.
• Can result in cells with abnormal numbers of chromosomes.

Outcomes of Meiosis

• Starts with a diploid cell.
• Results in four haploid cells, each with one chromatid (now called a chromosome).

Specific Conditions

• Trisomy: When nondisjunction results in three copies of a chromosome.
• Monosomy: Results in cells with only one copy of a chromosome.

Mitosis

• Similar process of chromosomal separation as in meiosis.

Errors in Chromosomal Segregation

• Nondisjunction in Meiosis or Mitosis:
  • Leads to abnormal chromosome numbers.
  • Affects both autosomes and sex chromosomes.

Disorders Due to Nondisjunction

• Turner Syndrome: One X chromosome in females.
• Klinefelter Syndrome: XXY condition in males.
• Down Syndrome: Trisomy 21, excess of chromosome 21.

Implications for Gamete Fusion

• Abnormal gametes result in diploid cells with unusual chromosome numbers when fused with normal gametes.