UNUSUAL SEGREGATION OF T(11-22) RESULTING FROM CROSSING-OVER FOLLOWEDBY 3 1 DISJUNCTION AT MEIOSIS-I/

Reciprocal translocation t(11;22)(q23;q11) is of particular interest b ecause the unbalanced offspring of the translocation carriers usually present with a supernumerary derivative chromosome 22. This common unb alanced karyotype is the result of 3:1 chromosome segregation during m eiosis. We report the third case of a rare segregation pattern of a pa ternal 11;22 translocation. The proband's karyotype revealed the prese nce of a der(ll) and two copies of a der(22), i.e. 47,XX,t(11;22)(q23; q11), +der(22) t(11;22)pat. The karyotype is the result of paternal 3: 1 segregation after crossing-over involving the derived and the normal chromosome 22, as revealed by chromosome polymorphism analysis. Contr ary to the preferential maternal transmission of this common unbalance d translocation, the data from the literature, including our case, may suggest preferential paternal transmission of this rare type of unbal anced translocation.