1. Errors in Meiosis

2.  Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis. Nondisjunction may occur during meiosis 1 or meiosis 2 Abnormal number of chromosomes may result Non-disjunction is one of the Two major occurrences of Meiosis (The other is Crossing Over)

3.  Non-disjunction results in the production of zygotes with abnormal chromosome numbers

4. An abnormal chromosome number (abnormal amount of DNA) is damaging to the offspring.

5. Should the gamete with the chromosome pair be fertilized then the offspring may or may not develop properly or at all

6. If it occurs in one of the smaller genes… 13, 15, 18, 21, 22 There is some chance of viability Trisomy 21 and 22 may survive into adulthood If it occurs in one of the larger genes… There is a failure in early development and termination occurs

8.  Monosomy If an organism has Monosomy 23 it has only one chromosome in the 23 rd set. Usually occurs in one of two ways

9.  Trisomy If an organism has Trisomy 21, there are three chromosomes in the 21 st set.

10. Genetic Testing 4 Amniocentesis 4 Physician removes amniotic fluid from around the fetus. Cells are cultured for karyotype 4 Chorionic villus sampling 4 Narrow tube inserted through the cervix to suction out a sample of the placenta (fetal cells) 4 Immediate karyotype

11.  Down’s Syndrome – Trisomy 21  Turner’s Syndrome – Monosomy 23 (X)  Kleinfelter’s Syndrome – Trisomy 23 (XXY)  Edward’s Syndrome – Trisomy 18

15.  Fertile  Normal physically  Normal mentally  Increase in testosterone  Perhaps more aggressive  Normal lifespan  1 in 1,800 births

16.  Scarce beard  Longer fingers and arms  Sterile  Delicate skin  Low mental ability  Normal lifespan  1 in 1,100 births

19. Short, broad hands Stubby fingers Rough skin Impotency in males Mentally retarded Small round face Protruding tongue Short lifespan 1 in 1,250 births

21.  1 in 4400 births XX=80% XY=20%  Small head  Mentally retarded  Internal organ abnormalities  90% die before 5 months of age

22.  1 in 4400 births  96-98% do not survive to birth  No menstruation  No breast development  Small hips  Broad shoulders and neck  Other health issues can include heart disease, horseshoe shaped kidneys, learning disabilities