1. 1

2. CHROMOSOMES 2

3. CHROMOSOME NUMBER  All cells in the human body (SOMATIC CELLS) have 46 or 23 pairs of chromosomes  Called the DIPLOID or 2n number  GAMETES (eggs & sperm) have only 23 chromosomes  Called the MONOPLOID or 1n number 3

4. NONDISJUNCTION  Chromosomes may fail to separate during meiosis  Resulting gametes may have too few or too many chromosomes  Disorders:  Down Syndrome – three 21 st chromosomes  Turner Syndrome – single X chromosome  Klinefelter’s Syndrome – XXY chromosomes 4

5. NORMAL MALE 5 2n = 46

6. NORMAL FEMALE 6 2n = 46

7. MALE, TRISOMY 21 (DOWN’S) 7 2n = 47

8. FEMALE DOWN’S SYNDROME 8 2n = 47

9. KLINEFELTER’S SYNDROME 9 2n = 47

10. TURNER’S SYNDROME 10 2n = 45