organisation of DNA in the cell 1.2.1

• DNA is genetic material (deoxyribonucleic acid)
• A gene is a unit of inheritance that codes for a specific protein.
• genes code for proteins which give us our inherited characteristics
• normal cells have 2 copies of every gene (diploid)
• chromosomes are thread like structures made of DNA
• there are 4 different bases (a,c,t and g) and the order of these bases determines the order of the amino acids needed to make a protein
• a base always goes with t
• c base always goes with g
• chromosomes are found as 23 pairs (23 from mother and 23 from father)
• chromosomes are only visible with a light microscope when they supercoil just before a cell divides
• normal cells have 2 copies of each chromosome, both copies of each chromosome have genes with the same characteristics
• alleles are different versions of the same gene,
• xx = female xy = male
• largest to smallest: cell, nucleus, chromosome, gene, cell base
• the nucleus of the cell contains chromosomes, which are coiled lengths of DNA molecules
• each chromosome carries a large number of genes
• different genes control the development of different characteristics
• body cells normally have 2 copies of each chromosome, whcih are normally found in pairs