DNA and cell division
- Created by: emews
- Created on: 14-11-17 17:55
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- DNA and cell division
- DNA molecules are large and complex. They carry the genetic code that determines the characteristics of a living organism.
- Except for identical twins, each person’s DNA is unique. This is why people can be identified using DNA fingerprinting.
- DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next.
- A gene is a section of DNA that codes for a specific protein.
- The cell’s nucleus contains chromosomes. These are long threads of DNA, each made up of many genes.
- There are four different bases in DNA:
- thymine, T
- adenine, A
- guanine, G
- cytosine, C
- They always pair up in a particular way, called complementary base pairing:
- thymine pairs with adenine (T–A)
- guanine pairs with cytosine (G–C)
- The chromosomes in a pair carry the same genes in the same places. But there are different versions of the same gene.
- Different versions of the same gene are called alleles.
- In mammals, body cells are diploid. The chromosomesneed to be copied exactly so that new cells can be produced for:
- growth
- repair to damaged tissue
- replacement of worn-out cells
- Mitosis produces two genetically identical cells in which the number of chromosomes is the same as in the original cell.
- Meiosis is the type of cell division that produces gametes.
- Meiosis produces four genetically different haploid cells. Unlike mitosis, meiosis is a reduction division – the chromosome number is halved from diploid (46 chromosomes in 23 pairs in humans) to haploid (23 chromosomes in humans).
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