Genetics

• Sex determination


  • One feature of your phenotype is inherited not by a single gene or multiple genes but by a single pair of chromosomes
  • Humans have 23 pairs of chromosomes
  • In 22 cases, each chromosome in the pair is a similar shape
  • Each one has genes carrying information about the many different characteristics of your body
  • One pair of chromosomes is different - these are the sex chromosomes and they determine the sex of offspring
  • In human females the sex chromosomes are the same (XX)
  • In human males the sex chromosomes are different (XY)
  • The Y chromosome is very small and carries few genes other than those related to sexual characteristics
  • When the cells undergo meiosis to form gametes, one sex chromosome goes into each gamete
  • Human egg cells contain an X chromosome
  • Half of the sperm also contain an X chromosome and the other half contain a Y chromosome
  • The inheritance of sex can be shown using a Punnett square
• Meiosis


  1. Cells undergo meiosis to form gametes

  2. One sex chromosome goes into each gamete