Cell division~

• The nucleus contains the DNA.
• The structures found in the nucleus are the chromosomes.
• There are 46 chromosomes in a normal human body cell.
• Chromosomes are arranged in pairs.
• There are 23 pairs in normal human body cells.
• Chromosomes are made up of DNA.
• Chromosomes are linear arrangements of genes.
• Genes are sections of DNA.
• DNA stands for deoxyribonucleic acid.
• There are 2 types of cell division.
• The two types of cell division are mitosis and meiosis.
• There types of cells that divide by mitosis are normal body cells.
• Mitosis occurs for growth and repair of a cell.
• The original cell before division is known as the mother cell.
• The cells produced in the following division are known as daughter cells.
• In mitosis 2 daughter cells are produced each time cell divides.
• There are 46 chromosomes in a mother cell.
• Stages of mitosis:

  -Chromosomes double from 46 to 92.

  -The number of chromosomes then split into 2. (46 chromosomes in each)
• In mitosis the new cells that are produced are genetically identical. the word to describe this is a clone.
• Acronym to remember mitosis:

  M-making

  I-Identical

  T-two
• Meiosis occurs in the reproductive organs.
• The cells that are produced by meiosis are called gametes.
• The special name given to this type of cell in a female human is called an ova or egg.
• The special name given to this type of cell in a male human is called sperm.
• Meiosis occurs when making a baby.
• The female reproductive organs are called the ovaries.
• The male reproductive organs are the testicles.
• The female gametes are the eggs.
• The male gametes are sperm.
• When fertilisation occurs the sperm joins to the egg cell and forms a zygote.
• 46 chromosomes must be in a human zygote for it to be viable.
• Gametes have 23 chromosomes.
• The original cell before meiosis is known as the mother cell.
• The cells produced following meiosis are known as the daughter cells.
• Stages of meiosis:

  -The mother cell (contains 46 chromosomes) doubles to 92.

  -Then it splits back into 46.

  -Then is splits again to produce 4 daughter cells. (contain 23 chromosomes).

  (So essentially splits twice.)
• The cells that are produced in the last stage of meiosis are genetically different to the mother cell.
• This leads to differences in offspring.
• When mitosis is uncontrolled it can cause cancer.
• Uncontrolled mitosis causes genes to mutate.
• The factors that can increase your risk of developing cancer are:

  -Being exposed to ultra-violet rays, x-rays, toxic chemicals and radioactive substances.