The two normal types of sex chromosomes are XX and XY. Sex chromosomes determine the biological sex of an individual. Females have two X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY). During sexual reproduction, each parent contributes one sex chromosome, either an X or a Y, to their offspring. If an individual inherits an X chromosome from both parents, they will be female (XX), while if they inherit an X chromosome from their mother and a Y chromosome from their father, they will be male (XY). Therefore, the two normal types of sex chromosomes are XX and XY.