DNA, genes, chromosomes

• Gene

  section of DNA they contains a code for making a polypeptide and functional RNA, the code is a specific sequence of bases. 

  Polypeptides make proteins and so genes determine the proteins of an organisms 

  occupies fixed position on DNA called locus
• allele

  1 of a number of alternative forms of a gene
• Chromosomes

  DNA is stored in chromosome

  23 pairs, 46 chromosomes

  pairs of matching chromosomes are homologous pairs, same genes but can have different alleles
• In eukaryotes

  DNA is stored as chromosomes in nucleus, linear shape. DNA is wound around histones, this is called a nucleosome
• In prokaryotes

  DNA is in chromosomes, but DNA is shorter and circular, not around histones 

  similarly stored in chloroplast and mitochondria (short and circular)
• The genetic code

  degenerate - multiple triplets can code for an amino acid

  universal - the same triplet codes for the same amino acid in all organisms 

  non-overlapping - each base is only part of 1 triplet of bases