Abnormal Meiosis: Nondisjunction

Disorders Caused by Nondisjunction of Autosomal Chromosomes:   There only 3 autosomal trisomies that result in a baby that can survive for a time after birth; the others are too devastating and the baby usually dies in utero. There are no instances of autosomal monosomies surviving after birth.

Down Syndrome (trisomy 21): 47, XX, +21 or 47, XY, +21 The result of an extra copy of chromosome 21. Down syndrome alters the child's physical appearance either moderately or severely. characteristic facial features, short stature; heart defects, shorter lifespan

often sexually underdeveloped and sterile, usually some degree of mental retardation. Down Syndrome is correlated with age of mother but can also be the result of nondisjunction of the father's chromosome 21.

B. Patau syndrome (trisomy 13): 47, XY, +13 or 47,XX, +13 serious eye, brain, circulatory defects as well as cleft palate children rarely live more than a few months

C. Edward's syndrome (trisomy 18): 47, XX, +18 or 47, XY, +18 almost every organ system affected children with full Trisomy 18 generally do not live more than a few months.

Disorders Caused by Nondisjunction of Sex Chromosomes Can be fatal, but many people have these karyotypes and are just fine!

D. Monosomy X (Turner's syndrome): 45, XO the only viable monosomy in humans genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

E. Klinefelter’s Syndrome: 47, XXY genetically male individuals have male sex organs, but usually small testes and are sterile may have breast enlargement and other feminine body characteristics. Normal intelligence

F. Trisomic Females: 47, XXX   healthy and fertile - usually cannot be distinguished from normal female except by karyotype XYY Males: 47, XYY Individuals are somewhat taller than average and sometimes have below normal intelligence. Increased amounts of acne Normal sexual development