DNA and Cell division

• A gene is a short length of DNA which codes for a particular protein or characteristic
• DNA stands for deoxyribonucleic acid
• 3 sub units of DNA are sugar (deoxyribose) phosphate and bases
• 4 bases of DNA are adenine, guanine, cytosine and thymine
• The sides are formed from sugar and phosphate(sugar phosphate backbone)
• the rungs are formed from bases
• DNA is a double helix
• Base pairing

  Adenine pairs with thymine

  guanine pairs with cytosine
• Only difference between each individuals DNA is the order of the bases as no 2 people have the same sequence
• DNA provides a code to allow the cell to make the the proteins that it needs
• 3 bases code for a particular amino acid. This is called a base triplet
• in mitosis cells double by splitting in half and divide into 2 daughter cells with the same genetic make up
• each chromosome duplicates to produce 2 chromatids held together by a centromere
• mitosis is used in growth, replaces worn out cells and repairs damaged tissue
• meiosis has 2 divisions and produces 4 daughter cells
• meiosis takes place in the sex organs during the production of gametes (sex cells)
• meiosis produces gametes with half the number of chromosomes (reduction division)
• in meiosis the daughter cells are different than the parent cells
• random independent assortments give unique gametes to produce variation in offspring
• haploid number is the number of chromosomes in gametes (23)
• diploid number is the normal number of chromosomes in organisms (46)