2.  Occurs when chromosomes fail to separate during meiosis  EITHER  Homologues chromosomes during anaphase I  OR  Sister chromatids during anaphase

3.  Normal gametes n  Some gametes will have 2 copies of a chromosome  n + 1  Some gametes will not have any copies of that chromosome  n-1

6. TRISOMIC CELLMONOSOMIC CELL  Has one extra chromosome  2n + 1  Has one missing chromosome  2n - 1

7.  Normal Human fertilized egg (zygote)  46 chromosomes (2n)

8. Normal human sperm cell 23 chromosomes (n) Trisomic human fertilized egg (zygote) 47 chromosomes (2n + 1)

9. Abnormal human sperm cell 22 chromosomes Monosomic human fertilized egg (zygote) 45 chromosomes (2n – 1)

10.  Nondisjunction occurs frequently  If fertilized:  Results are usually devastating to zygote  Miscarriage occurs very early in the pregnancy  If zygote survives:  Results in syndrome  Caused by the abnormal dose of chromosomes

11.  Picture of organized chromosomes  Homologous chromosomes are paired  Shown :  From longest (#1) to shortest (#22)  Sex chromosomes at end

14.  Down’s Syndrome  Patau Syndrome (Trisomy 13)  Edward’s Syndrome (Trisomy 18)  Klinefelter Syndrome  Jacob’s Syndrome (XYY)  Trisomy X  Turner Syndrome (Monosomy X)

15.  Extra Chromosome 21

16.  Characteristic facial features  Round, full face  Large forehead  Slanted eyes  Short height  Enlarged tongue  Heart defects  Shorter life span  Wide range of mental handicap

17.  AKA Trisomy 13  Extra chromosome 13

18.  Serious eye, brain and circulatory defects  Cleft palate  Rarely live more than a few months

19.  AKA Trisomy 18  Extra chromosome 18

20.  Affects almost every organ  Mental handicap  Many physical deformities  Do not live more than a few months

21.  Sex chromosomes : XXY  Male (XY) with and extra X chromosome

22.  Male sex organs  Usually small testis  Sterile  Can not have children  Enlarged breasts  High pitched voice  May have mental handicap

23.  Sex chromosomes: XYY  Male (XY) with an extra Y chromosome

24.  Male sex organs  Taller than average  Below normal intelligence  Once thought to be associated with criminal and aggressive behaviour Proven untrue

25.  Sex chromosomes: XXX  Female (XX) with an extra X chromsome

26.  Female sex organs  May be taller than average  May have delayed speech or learning disabilities  Reproductively healthy  Fertile  Female usually unaware of condition

27.  AKA Monosomy X  Sex chromosomes: X  Missing 2 nd sex chromosome

28.  Female sex organs, but underdeveloped  Do not mature sexually  Sterile  Shorter than average  Thick neck  Normal intelligence  98 of fetuses die before birth