Sex determination

• Genetic inheritance controls the characteristics of all living things
• Human body cells have 23 pairs of chromosomes in the nucleus
• Twenty two pairs are autosomes, controlling characteristics, while one pair determines sex
• Males have XY sex chromosomes, females have XX sex chromosomes
• Human karyotypes show all chromosomes aligned in pairs, with sex chromosomes being different sizes (X and Y for males, XX for females)
• Genetic diagrams, like Punnett squares, show how chromosomes combine in zygotes
• Inheritance of biological sex is shown in genetic diagrams
• Possible combinations for offspring:

  • XX from both parents produce a girl (female phenotype from XX genotype)
  • XY from both parents produce a boy (male phenotype from XY genotype)
• Ratio of female to male offspring is 1:1, with a probability of 50% for XX and 50% for XY