CELL DIVISION

Why do cells divide?

• Growth
• Repair
• Old cells die
  

Mitosis is a cell division that produces two daughter cells that are identical in chromosome number and in combination, for example, a cell with 23 pairs of chromosomes will yield two daughter cells each with 23 pairs of chromosomes and have the same combination.

Cancer is uncontrollable mitosis. The cells continue to divide nonstop and are immortal.

• Meiosis is a cell division that produces the gametes or sex cells.
  
• Meiosis reduces the number of chromosomes in half. For example, if a cell has 46 chromosomes and it undergoes meiosis, it will make four daughter cells with 23 chromosomes each. Each of the cells produced by meiosis have a different combination.
  

When the cell is dividing, if it is producing a sperm or an egg it is meiosis, if not, mitosis.

Meiosis only occurs in the testis and the ovaries.

Fertilization is the union of the sperm and the egg. This union occurs in the fallopian tube

Fertilization restores the chromosome number of the organism.

Meiosis and fertilization are responsible for the variations in species.

Zygote is a fertilized egg.

After the zygote is formed, the cell divides by mitosis and differentiates into the new structures of the organism.

Note: The advantage of sexual reproduction is variation.

Questions

• What is mitosis?
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• How are cell produced by mitosis different from cells produced by meiosis?
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• Explain fertilization.
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• Where does fertilization take place?
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• What is the significance of fertilization?
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• What are zygotes?
  

• In what structures of the male/female reproductive system does meiosis occur?

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