Chromosome abnormalities

Trisomy 21

Down syndrome; three copies of chromosome 21

1. An affected person has distinctive facial features And a unique pattern of hand creases

Chromosomal deletion

Results in the loss of one or more genes

1. Can cause cri du chat “cry of the cat” syndrome

2. Can also cause severe intellectual disabilities and developmental delays

Chromosomal duplication

Produces multiple copies of part of a chromosome

1. Causes Fragile X chromosome (repeated copies of a three base sequence - CGG - on the X chromosome)

Chromosomal inversion

Errors in crossing over; a part of a chromosome flips and reinserts, changing the gene sequence

1. All genes are still present

Chromosomal translocation

Crossing over occurs between nonhomologous chromosomes

1. Often break genes which can cause leukemia or other cancers

XXX

Triple X syndrome

1. 1 in 1500 females

2. Tall stature, menstrual irregularities, increased risk of giving birth to XXX daughters or XXY sons

XXY

Klinefelter syndrome or XXY syndrome

1. 1 in 750 males

2. Variable, but often include sexual underdevelopment, long limbs, large hands and feet, and development of breast tissue

XYY

Jacob’s or XXY syndrome

1. 1 in 1000 males

2. Often few noticeable symptoms; tall stature, acne, problems with speech and reading

XO

Turner sundrome

1. 1 in 2000 females

2. Short stature, sexual underdevelopment and infertility