Revision Notes

17.1.2 Inheritance of Sex

XX & XY Chromosomes

  • Sex, or gender, is determined by an entire chromosome pair (as opposed to most other characteristics that are just determined by one or a number of genes)
  • Females have the sex chromosomes XX
  • Males have the sex chromosomes XY
  • As only a father can pass on a Y chromosome, he is responsible for determining the gender of the child

Sex chromosomes, IGCSE & GCSE Biology revision notesSperm cells determine the sex of offspring


  • The inheritance of gender can be shown using a genetic diagram (known as a Punnett square), with the X and Y chromosomes taking the place of the alleles usually written in the boxes

Inheritance of sex, IGCSE & GCSE Biology revision notesPunnett square showing the inheritance of gender

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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