10. Major conditions changes in chr-18 18 p- There is a missing piece from the short arm of chromosome 18. 18q- There is a missing piece from the long arm of chromosome 18. If the missing piece is close to the centromere, it is called proximal 18q-. If the missing piece is close to the end of the chromosome, it is called distal 18q-.
11. Major conditions changes in chr-18 Ring 18 One of the copies of chromosome 18 forms a ring, and material is lost from both the long and short arm. Tetrasomy 18p An extra chromosome is present. This chromosome is made up of two copies of the short arm of chromosome 18.