AQA A Level Biology复习笔记8.2.1 Totipotent Cells

Totipotent Cells


  • A stem cell is a cell that can divide (by mitosis) an unlimited number of times
  • Each new cell that is produced when a stem cell divides has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell (by a process known as differentiation)
  • This ability of stem cells to differentiate into more specialised cell types is known as potency
  • There are three types of potency:
    • Totipotency
    • Pluripotency
    • Multipotency


Totipotent Cells

  • Totipotent cells can divide and produce any type of body cell
  • This type of stem cell is also referred to as 'embryonic stem cells
  • Totipotent cells exist for a limited time in early mammalian embryos, as well as in extra-embryonic cells (the cells that make up the placenta)
  • The zygote formed when a sperm cell fertilises an egg cell is totipotent, as are the embryonic cells up to the 16-cell stage (morula) of human embryo development
  • Initially, the totipotent cells in the embryo are unspecialised
  • During development, totipotent cells begin to translate only part of their DNA, which results in cell specialisation
  • These specialised cells then form tissues and are no longer classed as totipotent
  • There are no totipotent cells present in the later stages of development as cells lose their ability to differentiate into any cell type