Essay structure

• Stem Cells-

  1. There are embryonic and tissue stem cells
  2. All genes in embryonic stem cells can be switched on embryonic stem cells are pluripotent
  3. So they can differentiate into all cell types
  4. Tissue stem cells are involved in growth and repair and renewal of cells found in that tissue
  5. Tissue stem cells are multipotent.
  6. For example, blood stem cells located in bone marrow can give rise to red blood cells, platelets, phagocytes and lymphocytes.
•  Somatic Cells-

  1. Somatic  cells are any cell in the body other than cells involved in reproduction
  2. Somatic cells are diploid/have 23 pairs of homologous chromosomes.
  3. Somatic stem cells divide by mitosis to form more somatic cells
• Germline Cells-

  1. Germline cells are gametes (sperm and ova) and the stem cells that divide to form the gametes.
  2. Germline stem cells divide by mitosis and by meiosis
  3. Germline stem cells divide by mitosis to produce more diploid germline stem cells
  4. The nucleus of a germline stem cell can divide by mitosis to maintain the diploid chromosome number.
  5. Diploid cells have 23 pairs of homologous chromosomes
  6. Germline stem cells divide by meiosis to produce haploid gametes.
  7. The nucleus of a germline stem cell can divide by meiosis.
  8. It undergoes two divisions
  9. Haploid gametes contain 23 single chromosome