Difference Between Robertsonian Translocation and Isochromosome

The key difference between Robertsonian translocation and isochromosome is that Robertsonian translocation is a form of chromosomal translocation that involves the fusion of whole long arms of two acrocentric chromosomes while isochromosome is an abnormal unbalanced chromosome which has two identical arms due to duplication of one arm and deletion of the other.

Robertsonian translocation and isochromosome are two chromosomal abnormalities. In Robertsonian translocation, certain types of chromosomes are attached to each other. It is the most common form of translocation in humans. Isochromosome, on the other hand, is an abnormal chromosome which has two identical arms. These arms of isochromosome are mirror images of each other.

CONTENTS

1. Overview and Key Difference
2. What is Robertsonian Translocation
3. What is Isochromosome
4. Similarities Between Robertsonian Translocation and Isochromosome
5. Side by Side Comparison – Robertsonian Translocation vs Isochromosome in Tabular Form
6. Summary

What is Robertsonian Translocation?

Robertsonian translocation is the most common type of chromosome rearrangement known in humans. It is a form of chromosomal translocation that occurs by the fusion of whole long arms of two acrocentric chromosomes. This results in one large metacentric chromosome and one small fragment. About 1 in 1000 people are born with this chromosome rearrangement. Generally, acrocentric chromosomes 3, 14, 15, 21 and 22 in humans undergo Robertsonian translocation. Most common forms of Robertsonian translocations are between chromosomes 13 and 14, between 13 and 21, and between 21 and 22 in humans. Though it is a chromosomal abnormality, in balanced form and does not cause health problems.

Figure 01: Robertsonian Translocation

However, in unbalanced form, it can cause genetic disorders such as Down syndrome (trisomy 21) and Patau syndrome (trisomy 13). Moreover, it can increase the incidence of infertility and risk of genetic imbalances among their offspring.

What is Isochromosome?

Isochromosome is an abnormal chromosome which consists of two copies of either the long arm or the short arm. The arms of isochromosome are mirror images of each other. It is an unbalanced structural abnormality.

Figure 02: Isochromosome

Isochromosomes are formed due to the duplication of one arm and the loss of the other arm.  Then the cells will have only a single copy of the genetic material in the arm present in the normal member of the homologous pair. In simple words, the cells which have an isochromosome have trisomy for the arm that was duplicated and monosomy for the arm that was deleted. Similar to Robertsonian translocation, isochromosome formation is a frequent chromosomal aberration in humans. Turner syndrome and Neoplasia are two consequences of isochromosome formation.

What are the Similarities Between Robertsonian Translocation and Isochromosome?

• Both Robertsonian translocation and isochromosome formation are common in acrocentric chromosomes.
• In both processes, participating chromosomes break at their centromeres.

What is the Difference Between Robertsonian Translocation and Isochromosome?

Robertsonian translocation is a form of chromosomal translocation in which two acrocentric chromosomes fuse at their centric ends while isochromosomes are chromosomes composed of mirror images of one of the arms of the chromosome. So, this is the key difference between Robertsonian translocation and isochromosome. The fusion of whole long arms of two acrocentric chromosomes takes place in Robertsonian translocation while duplication of one arm and deletion of the other takes place in isochromosome formation.

Moreover, another difference between Robertsonian translocation and isochromosome is their consequences. Trisomy 13 (Patau syndrome) and trisomy 21 (Down syndrome) are two consequences of Robertsonian translocation while Turner syndrome and Neoplasia are two consequences of isochromosome formation.

Below infographic tabulates the differences between Robertsonian translocation and isochromosome.

Summary – Robertsonian Translocation vs Isochromosome

In Robertsonian translocation, two acrocentric chromosomes break at their centromeres and the long arms fuse to form a single, large chromosome with a single centromere. In isochromosome formation, centromeres of the chromosomes divide transversely and the union of two identical arms takes place. As a result, isochromosome has two identical arms which are mirror images of each other. Thus, this is the summary of the difference between Robertsonian translocation and isochromosome.

Reference:

1. “Robertsonian Translocation.” Overview | ScienceDirect Topics, Available here.
2. “Isochromosome”. En.Wikipedia.Org, 2020, Available here.

Image Courtesy:

1. “Translocation Robertsonian” By UPO649 1112 mreycor1 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Isochromosome” By Kazulanth at English Wikipedia – Transferred from en.wikipedia to Commons. (Public Domain) via Commons Wikimedia

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