Inheritance of sex

• Human chromosomes


  • 23 pairs
  • 22 pairs contain genes for inherited characteristics
  • 1 pair determines sex
• Sex chromosomes in males

  X and Y
• Sex chromosomes in females

  X and X
• Gametes produced by a couple

  1. Woman's gametes have X chromosome

  2. Man's gametes have X or Y chromosome
• Offspring sex chromosomes


  • 50% have XX (female)
  • 50% have XY (male)
• Offspring sex ratio is 1:1 (male:female) on average
• Actual offspring sex can vary from 1:1 ratio due to probability
• There are plenty of questions on the inheritance of sex in the revision workbook