ความสำคัญของไมโทซิส

Why mitosis 有丝分裂 matters

• Mitosis is nuclear division that makes two genetically identical 遗传上相同 daughter cells.
• Identical copies are exactly what a body needs to grow and repair itself.
• But the same process, out of control, causes tumours 肿瘤.

What mitosis is for

• growth of a multicellular organism (more cells).
• replacement of dead or damaged cells.
• repair of tissues by making new cells.
• asexual reproduction 无性生殖 — one parent producing identical offspring.

Each new cell carries exactly the same genes as the parent.

The mitotic cell cycle: interphase then mitosis and cytokinesis

Stem cells 干细胞

• A stem cell is an unspecialised 未分化 cell that can:
  • keep dividing by mitosis, and
  • differentiate 分化 (change) into specialised cell types.
• They are the source of new cells for replacing losses and repairing tissues.

A stem cell can keep dividing or differentiate into many specialised cell types

A stained onion root tip: several cells are caught dividing

When control is lost

• The cell cycle is normally tightly controlled, so cells divide only when needed.
• If that control is lost, a cell divides again and again without stopping.
• This uncontrolled division produces a lump of cells — a tumour.

When cell-cycle control is lost, a cell divides over and over, building up into a tumour

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