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

G. XYY Males: 47, XYY - Individuals are somewhat taller than average and sometimes have below normal intelligence. - Increased amounts of acne- Normal sexual development