Inheritance of Sex

• How many pairs of chromosomes do humans have?

  23 pairs
• What do the 23 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
• What are the possible sex chromosomes in the offspring from a male and female?

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

  1 to 1
• What does the ratio of offspring represent?

  Probabilities of male and female births
• Can a couple have all male or all female offspring?

  Yes, it's possible
• What are the key points about sex chromosome inheritance?

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