Inheritance of sex

• How many pairs of chromosomes do humans have?

  23 pairs
• What do the 22 pairs of chromosomes determine?

  Inherited characteristics
• What are the sex chromosomes in males?

  X and Y
• What are the sex chromosomes in females?

  X and X
• How do the gametes of a female differ from those of a male regarding sex chromosomes?

  Females have only X chromosomes
• What is the composition of male gametes regarding sex chromosomes?

  Half X and half Y chromosomes
• If a couple has offspring, what are the possible combinations of sex chromosomes?

  XX for female, XY for male
• What is the average ratio of female to male offspring?

  1 to 1
• Why might a couple have several offspring of the same sex?

  Because of probabilities in inheritance
• Where can students find questions on the inheritance of sex?

  In the revision workbook
• What are the key points about sex chromosome inheritance?

  • Males have XY chromosomes
  • Females have XX chromosomes
  • Female gametes contain only X chromosomes
  • Male gametes contain X and Y chromosomes
  • Offspring can be XX (female) or XY (male)
  • Average ratio of female to male is 1:1