Chromosome Numbers in Mitosis and Meiosis

Introduction

• Chromosome numbers can be confusing in the context of mitosis and meiosis.
• Human body cells have 46 chromosomes; human sex cells (gametes) have 23.

Structure of Chromosomes

• Chromosomes are composed of DNA and protein.
• DNA is highly condensed and organized into chromosomes for cell division.
• Chromosomes can exist as:
  • Single chromatid
  • Two sister chromatids joined at a centromere

Counting Chromosomes

• Chromosome count is based on the number of centromeres.
• Interphase precedes mitosis and meiosis and involves chromosome duplication.
  • 46 chromosomes with 46 chromatids initially.
  • Post-duplication: 46 chromosomes, each with 2 chromatids (92 chromatids total).

Mitosis

• At anaphase, sister chromatids separate resulting in 92 separate entities (could be argued as 92 chromosomes).
• At the end of mitosis, two daughter cells each with 46 chromosomes.
• Daughter cells are identical to the original cell.

Meiosis

• Begins with 46 chromosomes with single chromatids.
• Post-duplication: 46 chromosomes with 92 sister chromatids.
• Meiosis I:
  • Results in 2 cells, each with 23 chromosomes (46 chromatids in total).
• Meiosis II:
  • Results in 4 cells, each with 23 chromosomes and 23 chromatids.
• Meiosis involves reduction division, resulting in cells with half the original number of chromosomes.

Key Concepts

• Chromosome counting revolves around centromere counting and definitions of chromatids.
• Mitosis results in identical daughter cells, while meiosis results in genetically unique cells with half the original chromosome number.

Conclusion

• Understanding chromosome numbers heavily relies on knowing the definitions and process of cell division.
• Encouragement to stay curious and explore further.