 The extra chromosome 21 material that causes Down syndrome may be due to a Robertsonian translocation.The long arm of chromosome 21 is attached to the long arm of another chromosome, often chromosome 14 [46,XX,t(14;21)] or itself [called an isochromosome, 45,XX,t(21;21)(q10;q10)] as seen in the translocation karyotype figure.Translocation Down syndrome can be "de novo"; that is, not inherited but occurring at the time of an individual's conception, or may be inherited from a parent with a balanced translocation.