Absence of constitutive heterochromatin in a partially identified supernumerary marker chromosome.

A retarded child with multiple malformations was found to have a karyotype 47,XY,de1(11)(11 pter leads to q21:), +mar(11 qter leads to q21::?). The mitotically stable centric marker had no demonstrable C heterochromatin. Phenotype-karyotype correlation and the role of C heterchromatin in phenotypic effects are discussed.