CHROMOSOMAL ABNORMALITIES
What are chromosomal abnormalities?
• These alterations can be detected by studying the affected person´s karyotype.
• There are many types of chromosomal abnormalities. However, they can be organized into two basic groups:
▫ Numerical abnormalities:
▫ Structural abnormalities
Normal karyotype
• There are 46 chromosomes (23 homologous ones)
• Homologous chromosomes are evenly banded)
Numerical abnormalities
• Monosomy: an individual is missing one of the chromosomes from a pair.
• Trisomy: an individual has three chromosomes instead of a pair
Numerical abnormalities. MONOSOMY
• Turner´s syndrome (XO):
▫ Disorder affecting women
▫ An only X chromosome in pair 23 (sex chromosomes)
▫ Clinical symptoms:
Sterility and underdeveloped genitals
Short height
▫ Frequency: 1 / 3300 birhts
Numerical abnormalities. TRISOMY
• Klinefelter´s syndrome (XXY):
▫ Disorder affecting men
▫ Two X chromosomes and one Y chromosome in pair23 (sex chromosomes)
▫ Clinical symptoms:
Small genitals and sterility in some cases
Mild learning disabilities
▫ Frequency: 1.4 / 1000 births
Numerical abnormalities. TRISOMY
• Triple X syndrome (XXX) = super female
▫ Disorder affecting women
▫ Three X chromosomes in pair 23 (sex chromosomes)
▫ Clinical symptoms:
Mild learning disabilities
Delayed development of speech and motor skills
▫ Frequency: 1 / 1000 births
Numerical abnormalities. TRISOMY
• XYY syndrome:
▫ Disorder affecting men
▫ One X chromosome and two YY in pair 23 (sex chromosomes)
▫ Clinical symptoms:
Skeleton malformations (very tall)
Moderate learning disabilities and aggressiveness
▫ Frequency: 1 / 2000 births
Numerical abnormalities. TRISOMY
• Down´s syndrome:
▫ Disorder affecting women or men (not sex-linked)
▫ Three chromosomes in pair 21
▫ Clinical symptoms:
Varying degrees of intellectual disability
Flat head syndrome (brachycephaly)
Unusually small chin, skin folds at the edge of the eyes, round face, shorter limbs.
Various problems with eyesight and heart.
▫ Frequency: 1.5 / 1000 births
Numerical abnormalities. TRISOMY
• Edwards´s syndrome:
▫ Disorder affecting women and men (not sex-linked)
▫ Three chromosomes in pair 18
▫ Clinical symptoms:
Severe intellectual disability
Kidney and heart malformations
Arrested growth and abnormal development of limbs
Short neck and sternum
▫ Frequency: 1 / 6766 births
Numerical abnormalities. TRISOMY
• Patau´s syndrome:
▫ disorder affecting women and men (not sex-linked)
▫ Three X chromosomse in pair 13
▫ Clinical symptoms:
Intellectual disability
Heart, genital, finger and brain malformations
Missing palate
Deformed feet
▫ Frequency: 1 / 4600 births
Structural abnormalities
• Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.
Structural abnormalities
• Translocations:A portion of one chromosome is transferred to another chromosome.
Structural abnormalities
• Inversions: A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted.
References
• http://www.genome.gov/11508982#al-5
• http://www.dnaftb.org/#classical
• http://learn.genetics.utah.edu/content/disorders/chromosomal/
• Cabrera. A. et al. 2012. 4 ESO. Biology and Geology. Oxford Education