Visual communication aid: Robertsonian chromosome translocations

There are two communication aids available to view and download (.pdf) for this topic:

• Robertsonian chromosome translocations: overview
• Robertsonian chromosome translocations: pregnancy outcomes

Double-sided printing in colour is recommended (but not required). All content is also included below in an accessible format.

More information about these and other VCAs is available in this article.

We all have over 20,000 genes, which provide instructions for how our body works. Genes are made of DNA. Our genes are packaged into structures called chromosomes. ​

Individuals usually have 46 chromosomes in each cell in their body. These are arranged into 23 pairs. ​

Sometimes, when cells divide to form eggs or sperm, or during early development of a baby, chromosomes may break and repair themselves incorrectly. ​

Robertsonian translocations occur when two chromosomes, known as acrocentric chromosomes (chromosomes 13, 14, 15, 21 and 22), fuse together. This means an individual’s genetic information has a different arrangement than usual.

Generally, Robertsonian translocations are balanced and do not affect an individual’s health. A small amount of DNA, known as the short arm of a chromosome, is usually lost but this does not cause health problems (figure 1).

If either parent of a pregnancy carries a balanced Robertsonian translocation, this can affect the outcome of the pregnancy.

Figure 1: Example of a Robertsonian chromosome translocation
(View larger image)

When either parent of a pregnancy carries a Robertsonian translocation, there are several possible outcomes (figure 2):​

1. The pregnancy does not carry a translocation.​
2. The pregnancy carries the same balanced Robertsonian translocation as their parent. In general, this has no effect on the pregnancy or health of the child.​
3. The pregnancy inherits an unbalanced form of the translocation. This means the pregnancy has inherited too many or too few chromosomes. Depending on the chromosomes involved, this may lead to pregnancy loss, or having a child with a chromosome condition.

Potential outcomes of a pregnancy may differ depending on the chromosomes involved. Some outcomes may therefore be more likely than others.

Figure 2: Potential outcomes of a pregnancy when one parent carries a Robertsonian translocation
(View larger image)

• Chromosomes: Packages of DNA which are found in our cells​.
• Acrocentric chromosomes: The term used for certain chromosomes with very small short arms (chromosomes 13, 14, 15, 21 and 22).
• Balanced translocation: The term used when two or more chromosomes have been rearranged, but no DNA is lost or gained​.
• Unbalanced translocation: The term used when a chromosome rearrangement has caused DNA to be lost or gained.
• Trisomy: Having an extra copy of a chromosome.
• Monosomy: Having just one copy of a chromosome instead of two.

For patients

• Unique: Robertsonian Translocations