• Genes are sections of DNA which contain coded information for making polypeptides. These make the proteins that determine the characteristics of organisms.
  • Chromosomes contain one very long molecule of DNA. Each molecule carries many genes
  • In body cells (somatic), chromosomes occur in homologous pairs. Each pair consists of a copy of one maternal and one paternal chromosome.
  • Genes that code for the same polypeptide occupy the same relative position on homologous chromosomes. This position is called the gene locus.
  • Genes can have different forms, called alleles. The coded information in alleles differs, so the polypeptides they code for also differ.