Cytogenetics

Question 1

Robertsonian Translocations

Answer 1

o Robertsonian – between acrocentric (Robertsonian chromosomes)
▪ Balanced carriers have 45 chromosomes
▪ Ex. 45, XY t(14;21)(q10;q10) OR 45, XY rob(14;21)(q10;q10)
▪ Can form isochromosomes when translocation is between two of the same acrocentric chromosomes (i.e. 21;21 translocation)
▪ 13;14 and 14;21 are most common
▪ For 14;21 translocation specifically
● Female risk for unbalanced offspring – 10-15%
● Male risk for unbalanced offspring – 1-2%

Question 2

Reciprocal Translocations

Answer 2

oReciprocal – interchange of material between two non-homologous chromosomes
▪Balanced reciprocal translocations are very common
● Approximately 70% are inherited
▪ Carriers at risk for multiple miscarriages/unbalanced offspring
▪ Caused by errors in meiotic segregation
▪ Balanced translocation carriers may have symptoms due to positional effects/fusion genes

Question 3

Philadelphia chromosome

Answer 3

● Philadelphia chromosome - t(9;22)(q34;q11) ABL/BCR and risk for CML
● Intellectual disability in some translocations
● Congenital anomalies in some translocations

Question 4

Inversions

Answer 4

oPericentric – includes the centromere
▪Can result in unbalanced offspring
oParacentric – does not include the centromere
▪Usually results in acentric fragments/dicentric chromosomes
▪Greater amounts of miscarriage