The Genome & Genes (Edexcel IGCSE Biology: Double Science)

• The entirety of an organism's DNA is known as its genome
• A gene is a section of a molecule of DNA
• Each gene within the genome codes for a particular sequence of amino acids
• These sequences of amino acids form different types of proteins
• Genes control our characteristics as they code for proteins that play important roles in what our cells do
• There are many different types of proteins e.g.
  • Structural proteins such as collagen found in skin cells
  • Enzymes
  • Hormones

• In the nucleus of a cell, the DNA double helix supercoils to form structures called chromosomes
  • Chromosomes are only visible during cell division
• Ordinary human body cells contain 23 pairs of chromosomes, meaning that they contain 46 chromosomes in total
  • This is a diploid number (often shown as 2n)
  • One chromosome from a pair is inherited from each parent
  • Each chromosome pair is called a homologous pair
• Genes are found in specific locations on the chromosomes, these locations were identified in the human genome project

Genes are short lengths of DNA that code for a protein. They are found on chromosomes.