What type of translocation can only result in trisomy or miscarriage when involving two copies of the same chromosome?

The type of translocation that can only result in trisomy or miscarriage when involving two copies of the same chromosome is a Robertsonian translocation. This genetic alteration occurs when two acrocentric chromosomes (chromosomes with very short p arms) fuse near the centromere to form a single chromosome.

In the case of a Robertsonian translocation involving two copies of the same chromosome, the resultant formation can lead to an unbalanced gamete during meiosis. If such a gamete is fertilized, it can give rise to an embryo with an extra copy of that chromosome, resulting in trisomy for the genetic material, which often has significant developmental consequences and can lead to miscarriage.

The unique nature of acrocentric chromosomes and the way they fuse mean that the balance of genetic material is highly sensitive. Miscarriage may occur more often if the genetic material is unbalanced. This is distinct from reciprocal translocations, which may also have risks associated with them but can be more balanced and sometimes result in viable pregnancies. Other structural rearrangements like pericentric and paracentric inversions do not typically lead to the same kind of scenarios involving chromosome copies directly leading to trisomy or miscarriage as seen with Robertsonian translocations.