Chromosomes and genes

• Sexual reproduction involves the joining (fusion) of male and female gametes (sperm and egg cells in animals).
• In sexual reproduction there is mixing of genetic information, which leads to variety in the offspring. The formation of gametes involves meiosis.
• The genetic material in the nucleus of a cell is composed of a chemical called DNA contained in the chromosomes.
• Human body cells contain 23 pairs of chromosomes. DNA is made of very large molecules in long strands, twisted to form a double helix.
• A gene is a small section of DNA on a chromosome.
• Each gene contains the code for a particular combination of amino acids to make a specific protein.
• The genome of an organism is made up of all the genes in the DNA of its body cells.