Learning Objective: At the end of this session, the learner will be able to explain the mechanism, chromosomal involvement, and clinical significance of Robertsonian translocation.
Robertsonian translocation is a chromosomal structural abnormality involving fusion between two acrocentric chromosomes. It is one of the most common types of chromosomal translocations seen in humans.
Mechanism
- Occurs when the long arms (q arms) of two acrocentric chromosomes (chromosomes with centromeres near their ends) fuse at the centromere.
- The short arms (p arms) are usually lost during this process.
- The resulting chromosome has a single centromere and contains most of the essential genetic material.
Activity:
Chromosomes Commonly Involved
| Chromosome Pairs | Examples of Associated Conditions |
|---|---|
| 13, 14 | Patau syndrome (trisomy 13) |
| 14, 21 | Down syndrome (trisomy 21 due to translocation) |
| 15, 21 | Rare cases of Down syndrome |
| 21, 22 | Rare translocations |
Types
| Type | Genetic Material Change | Clinical Outcome |
|---|---|---|
| Balanced Translocation | No loss or gain of significant genetic material | Usually phenotypically normal |
| Unbalanced Translocation | Missing or extra genetic material | May lead to miscarriage, stillbirth, or chromosomal imbalance (e.g., Down or Patau syndrome) |
Clinical Relevance
- Balanced carriers are usually asymptomatic but have a risk of producing abnormal gametes.
- During meiosis, gametes may be normal or unbalanced, leading to trisomy or monosomy in offspring.
- Genetic counseling is crucial for carriers.
