Lecture on Meiosis and Chromosome Abnormalities

Overview of Meiosis

• Meiosis:
  • Distinct from mitosis.
  • Produces haploid cells (gametes) from diploid cells.
  • Essential for sexual reproduction.

Diploid vs. Haploid

• Diploid Cells:
  • Body cells (somatic cells).
  • Contain 46 chromosomes in 23 pairs.
  • Receive chromosomes from both parents.
• Haploid Cells:
  • Germ cells (gametes like sperm and egg).
  • Contain 23 chromosomes.
  • Combine during fertilization to restore diploid number in a zygote.

Sexual vs. Asexual Reproduction

• Asexual Reproduction:
  • Single parent produces clone.
  • Efficient in stable environments (e.g., bacteria).
• Sexual Reproduction:
  • Gametes fuse to form a zygote.
  • Increases genetic variation and adaptability.

Meiosis Process

• Meiosis Steps:
  • Start with diploid cell (2N), duplicate DNA to 4N.
  • Undergo two divisions: Meiosis I and Meiosis II.
  • Results in four haploid cells.
• Crossing Over:
  • Occurs during prophase I.
  • Leads to genetic variation by exchanging DNA segments.

Meiosis I

• Prophase I:
  • Homologous chromosomes pair and exchange DNA (crossing over).
• Metaphase I:
  • Tetrads align in the middle.
• Anaphase I:
  • Homologous chromosomes separate.
• Telophase I:
  • Two diploid cells form, genetically different.

Meiosis II

• Similar phases to mitosis but results in haploid cells.
• End Product: Four genetically distinct haploid cells.

Meiosis in Males vs. Females

• Males:
  • One cell becomes four sperm cells.
  • Continuous production.
• Females:
  • One cell results in one egg due to uneven cytokinesis.
  • Limited number of eggs available from birth.

Chromosome Abnormalities

• Structural Changes:
  • Inversion, duplication, insertion, deletion, translocation.
• Number Variations:
  • Euploid: Normal number.
  • Polyploid: More than two sets of chromosomes.
  • Aneuploidy: Abnormal number of a particular chromosome.
• Non-disjunction:
  • Improper chromosome separation leading to aneuploidy.
  • Can result in disorders like Down syndrome (trisomy 21), Edward syndrome, Patau syndrome.

Impact of Age on Chromosome Abnormalities

• Increased risk with maternal age.
• Non-disjunction more common in older women leading to potential genetic abnormalities.

Conclusion

• Importance of meiosis in genetic diversity and reproduction.
• Influence of chromosomal abnormalities on health and development.

Review materials provided and prepare questions for further discussion.