Sex chromosomes

• Pairs of chromosomes in every human body cell

  • 23 pairs
• 23rd pair of chromosomes

  Sex chromosomes
• XY

  Males have an X and a Y chromosome
• XX


  Females have two X chromosomes
• The Y chromosome causes male characteristics
• The lack of a Y chromosome causes female characteristics
• Gene on the Y chromosome


  Makes an embryo develop into a male as it grows
• Sex inheritance


  Shows the sex chromosomes rather than different alleles
• Offspring genotypes

  • Two XX genotypes and two XY genotypes
• There's a 50% chance of having either a boy or a girl
• There is a 50:50 ratio of boys to girls
• This is a genetic diagram

  50/50