Reproduction, the genome and gene expression

• Meiosis

  Formation of 4 non-identical cells from one cell
• Mitosis


  Formation of 2 identical cells from one cell
• Sexual reproduction


  Involves joining of male and female gametes
• Gametes are formed by meiosis as they are haploid (containing half the normal chromosome number)
• A human cell has 46 chromosomes (23 pairs)
• Each gamete has 23 chromosomes, with one from the mother and one from the father
• The genetic information from each parent is mixed in the offspring, producing variation
• Asexual reproduction involves one parent and leads to genetically identical offspring (clones)
• Meiosis


  1. Cell doubles its chromosomes

  2. Cell divides into two cells

  3. Cell divides again producing 4 cells each with half the original chromosome number
• Advantages of sexual reproduction

  • Produces variation
  • Allows natural selection
  • Allows selective breeding
• Advantages of asexual reproduction

  • Only one parent needed
  • Uses less energy and is faster
  • Can produce many identical offspring in favourable conditions
• DNA


  Genetic material in the nucleus composed of chemical called DNA