ABNORMAL MEIOSIS

NONDISJUNCTION: when 2 homologous chromosomes move to the same pole during meiosis. One daughter cell will be missing one chromosome while the other will have an extra chromosome.

TRISOMY: the gamete with 24 chromosomes joins with a normal gamete (23) to form a zygote with 47 chromosomes

MONOSOMY: the gamete with 22 chromosomes joins with a normal gamete (23) to form a zygote with 45 chromosomes

NONDISJUNCTION DISORDERS:

DOWN SYNDROME: an extra 21st chromosome, a trisomic disorder where a person has too much genetic information. Many varying traits such as full face, short, large forehead. Affects 1 in 600 babies. Mothers over 40 years of age have a 1 in 40 chance of having a Down Syndrome baby.

TURNER SYNDROME: when the sex chromosomes, pair 23, undergo nondisjunction to form a female with a single "X" chromosome. The zygote has 45 chromosomes, monosomic. Females are short, thick necks, sexually underdeveloped. Affects 1 in 10000 births (more miscarried).

KLINEFELTER SYNDROME: the zygote inherits two "X" chromosomes and a single "Y" chromosome, trisomic "XXY" as cells have 47 chromosomes. Child is male at birth, produce high estrogen levels at puberty, sterile. Affects 1 in 1000 births.

SUPERMALES: Unlike normal "XY" males these "XYY" males have 47 chromosomes, trisomic. Subnormal intelligence, taller, can be violent.

Technology to help diagnose disorders before birth:

  1. Amniocentesis, CVS (chorionic villus sampling), ultrasounds.
  2. KARYOTYPING: cells are stopped during metaphase with drugs, a photo is taken of their chromosomes, homologous pairs (same size and shape) are matched together and counted