Chromosome abnormalities

Balanced chromosome rearrangement

• All the chromosomal material is present

Unbalanced chromosome rearrangement

• Extra or missing chromosomal material, usually 1 or 3 copies of gene
• Causes major developmental problems

Aneuploidy

• Whole extra or missing chromosome
• X chromosome aneuploidy better tolerated because of X chromosome inactivation

Translocation

• Rearrangement of chromosomes

Robertsonian translocation

• Two acrocentric chromosomes stuck end to end

• Increased risk of trisomy in pregnancy

  

Reciprocal translocation

• Two broken off chromosome pieces of non-homologous chromosomes are exchanged

Specific karyotypes

• 47XY +21 (trisomy 21) - Down’s syndrome
• 47 XY +14 (trisomy 14) - miscarriage