1.1

• Division of Somatic and Germline Cells

  Somatic cells: Any cell in the body other than cells involved in reproduction

  Somatic stem cells: Divide by mitosis to form more somatic cells

  Human diploid somatic cells have 23 pairs of homologous chromosomes i.e. 46 chromosomes
• Germline cells


  Gametes (sperm and ova)

  Germline stem cells: Situated in the testes and ovaries, can divide by mitosis and meiosis
• Mitosis of germline stem cells

  Nucleus of germline stem cell divides by mitosis to self-renew and maintain diploid chromosome number
• Meiosis of germline stem cells

  Nucleus of germline stem cell divides by meiosis, separating homologous chromosomes and then chromatids, to generate haploid gametes with 23 single chromosomes
• Diploid cells


  Have 23 pairs of homologous chromosomes
• Haploid cells


  Have 23 single chromosomes
• Cellular Differentiation


  Process by which cells become specialised to a particular function

  Once differentiated, a cell only expresses the genes/makes the proteins characteristic of that cell type, allowing it to carry out specialised functions
• Self-renewal


  A stem cell's ability to divide and produce copies of itself
• Embryonic Stem Cells

  Cells of the early embryo that are pluripotent - all their genes can be switched on, allowing them to differentiate into any cell type
• Tissue Stem Cells


  Multipotent - can differentiate into all the types of cell found in a particular tissue
• Therapeutic Uses of Stem Cells

  Stem cells can self-renew under the right conditions in the laboratory and be used to repair damaged or diseased organs
• Other Uses of Stem Cells

  Used as model cells for scientists to study cellular processes, how diseases develop, or for drug testing

  Stem cell research provides information on cell processes like growth, differentiation and gene regulation
• Ethical Issues using Stem Cells
• Cancer

  Cancer cells fail to respond to normal regulatory cell signals and divide excessively to produce a mass of abnormal cells called a tumour

  Cancer cells may fail to attach to each other and can spread throughout the body to form secondary tumours
• Differentiation of Stem Cells
• Research into Stem Cells and their Therapeutic Value
• Stem Cells There are embryonic and tissue stem cells

  Embryonic stem cells are pluripotent - all their genes can be switched on, so they can differentiate into all cell types

  Tissue stem cells are multipotent - they can differentiate into all the types of cell found in that tissue

  For example, blood stem cells in bone marrow can give rise to red blood cells, platelets, phagocytes and lymphocytes
• B. Somatic Cells

  • Somatic cells are any cell in the body other than cells involved in reproduction

  Somatic cells are diploid - have 23 pairs of homologous chromosomes

  Somatic stem cells divide by mitosis to form more somatic cells
• C. Germline Cells

  • Germline cells are gametes (sperm and ova) and the stem cells that divide to form the gametes

  Germline stem cells divide by mitosis to produce more diploid germline stem cells, maintaining the diploid chromosome number

  Germline stem cells divide by meiosis to produce haploid gametes with 23 single chromosomes

  The nucleus of a germline stem cell can divide by meiosis, separating the homologous chromosomes and then the chromatids