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Translocation: Definition & Types

Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

Genes can become mixed up and change between one set of chromosomes to another in a process called translocation. Learn more about types of translocation and their effects on an organism.

Translocation Basics

Imagine you are rolling long, rope-like pieces of playdough. You crisscross the two pieces of rope, creating an X-shaped pattern. For each color, you make a duplicate pair and set them next to each other. When your back is turned, someone cuts a section of rope from one color and replaces it with another. When you return, you see that two of your ropes have had sections swapped out, leaving you with two ropes that are mix-and-matched.

This is similar to what happens when chromosomal translocation occurs. Each X-shaped playdough pair is a set of chromosomes, which contains genetic DNA information. Normally, each pair of chromosomes is similar. Matching pairs are called homologous chromosomes; the prefix homo is Greek for 'same'. The only exception is sex chromosomes, which do not have a pair. The rest are paired autosomal chromosomes.

Translocation
Translocation

In the playdough mix-match, it was not two homologous (same colored) chromosomes that were swapped. Instead, two different colored X's, called nonhomologous chromosomes (think of 'non-homo' meaning 'not the same'), were exchanged. Translocation occurs when a section of genes from two nonhomologous chromosomes are interchanged. More specifically, reciprocal translocation took place in the above example, because the mismatched pieces were interchanged on the nonhomologous chromosomes.

Heterozygous Reciprocal Translocation

Remember that each chromosome is shaped like two ropes that cross each other to form an X shape. In addition, each has a matching homologous pair. Imagine each pair of normal chromosomes as the same color playdough pieces.

Sometimes one X, or chromosome, in the set has been left untouched, while the matching X has a section that has been exchanged. This is called a heterozygous reciprocal translocation, because one chromosome of the pair remains normal, while the other has an interchanged part. The prefix hetero means 'not the same,' signifying that the two pairs are no longer alike, since one chromosome has an abnormality.

Most organisms with a heterozygous reciprocal translocation are semi-sterile. They produce about half of the live offspring as an organism that did not have this genetic mutation. This is because, as the chromosomes divide during meiosis, a cellular process used in reproduction, there is a 50% chance of the offspring getting the mutation.

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