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
• How do the gametes of a woman differ from those of a man regarding sex chromosomes?

  All woman's gametes have X chromosomes
• What is the composition of a man's gametes regarding sex chromosomes?

  Half X and half Y chromosomes
• What are the possible sex chromosomes combinations in offspring from a male and female?

  XX or XY
• What percentage of offspring are expected to be female?

  50%
• What is the expected ratio of male to female offspring?

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

  Because these are just probabilities
• What are the key points about sex chromosome inheritance?

  • Males have XY chromosomes
  • Females have XX chromosomes
  • All female gametes carry X
  • Male gametes carry X or Y
  • Offspring can be XX (female) or XY (male)
  • Expected ratio: 50% female, 50% male