Development Of Organisms And Continuity Of Life: Nuclear Division

16.1 Nuclear Division

DNA And Chromosomes

• Chromosomes contain DNA → genetic information.
• Gene = length of DNA coding for a protein.
• Human diploid cell → 46 chromosomes (23 pairs).
• Haploid cell → half the chromosome number (23 in humans).

Key Terms

• Diploid nucleus → 2 sets of chromosomes (pairs).
• Haploid nucleus → 1 set of chromosomes.

Mitosis

• Nuclear division producing genetically identical cells.
• Maintains chromosome number (diploid → diploid).
• Roles:
  • Growth.
  • Repair of tissues.
  • Replacement of cells.
  • Asexual reproduction.

Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course

Stem Cells

• Unspecialised cells.
• Divide by mitosis to form daughter cells.
• Can specialise into different cell types.

Meiosis

• Reduction division → chromosome number halved (diploid → haploid).
• Produces gametes (sperm, egg, pollen).
• Results in genetic variation.
• Cells produced are genetically different.

Cancer

• Results from uncontrolled cell division.
• Tumours form, may spread.

Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course