What is the difference between a mutation and a chromosonal abnormality?

Degree. A mutation usually refers to a change in a gene changing its function. A chromosomal abnormality usually means a gross change to a chromosome like a loss of all or part of a chromosome (deletion) or the moving of one part of one chromosome onto another chromosome (translocation) causing abnormal cellular behavior. Deletions and translocations usually cause major problems. Mutations may be silent.