Chromosomal translocation

Our bodies have tiny parts called chromosomes.

These parts hold our instructions. Sometimes, these parts break. When they break, they can switch places. This is called a translocation.

Two parts might swap. Other times, they might stick together. This can change how a body grows. Some swaps are fine. Other swaps can cause health problems. These changes happen in our cells.

It is a big part of how we work.

Our bodies use chromosomes to hold instructions.

Sometimes, these parts break and move. This is called a translocation.

There are three main ways this happens. In a reciprocal translocation, two different chromosomes swap parts. This is a balanced change if no parts are lost. It is unbalanced if some parts are missing or extra. In a nonreciprocal translocation, one part moves to another. This is always unbalanced. The first chromosome loses parts, while the second one gains them.

A third way is a Robertsonian translocation. This happens when two chromosomes stick together. They fuse, or blend, into one large part. This can leave a person with only 45 chromosomes instead of 46.

These changes can affect how a body grows. Some can lead to cancer. For example, a change between chromosomes 9 and 22 causes leukemia.

Scientists find these changes by looking at a karyotype. A karyotype is a map of all the chromosomes in a cell.

Inside our cells, chromosomes hold the instructions for our bodies.

Sometimes, these chromosomes break and move to new places. This is called a translocation. It is a type of unusual rearrangement of the chromosomes. These changes can affect how a person grows or functions. They can even lead to health issues like cancer.

There are three main ways a translocation can work. In a reciprocal translocation, two different chromosomes swap pieces. This is called balanced if no genetic information is extra or missing. It is called unbalanced if the exchange is unequal. This means some genes are missing or extra. In a nonreciprocal translocation, one piece moves from one chromosome to another. This is always unbalanced because one chromosome gains material while the other loses it.

A third way is the Robertsonian translocation. This happens when two chromosomes get attached or fused together. They blend into one large chromosome. This can leave a person with only 45 chromosomes instead of 46. This type of change can happen with many different chromosome pairs. For example, a common one involves chromosomes 13 and 14. This happens in about 0.97 out of every 1,000 newborns. Some people with these changes might have a higher risk of having a child with Down syndrome.

Scientists have been studying these changes for a long time. In 1916, William R. B. Robertson saw a fusion in grasshoppers. In 1938, Karl Sax showed that X-rays could cause these changes in plants. Later, Barbara McClintock studied how chromosomes break and fuse in maize. A huge discovery happened in 1960 with the Philadelphia chromosome. This was the first time a chromosomal change was linked to human cancer. In 1973, Janet Rowley found that this was a translocation between chromosomes 9 and 22.

Today, we have amazing tools to see these tiny changes. In the 1970s, scientists used banding techniques to see patterns on chromosomes. In the 1980s, they used a method called FISH. This uses glowing probes to label specific DNA sequences. Now, in the 21st century, we use high-throughput DNA sequencing. This lets us see changes at a very tiny level. These tools help us understand how translocations lead to disorders like Emanuel syndrome. They also help us study how cells repair themselves after a break.

Chromosomal translocation is a phenomenon involving the unusual rearrangement of chromosomes. This occurs when segments of DNA break off and attach to different chromosomes. Such changes can affect how an individual's body grows, functions, or develops. These rearrangements can lead to significant changes in the genome. Some translocations result in the creation of a gene fusion. This happens when the translocation joins two genes that were previously separated.

There are three primary types of translocation: reciprocal, nonreciprocal, and Robertsonian. In a reciprocal translocation, two non-homologous chromosomes exchange parts. This can be balanced, meaning no genetic material is lost or gained. It can also be unbalanced, where the exchange is unequal. An unbalanced reciprocal translocation results in extra or missing genes. Nonreciprocal translocation involves a one-way transfer of genes from one chromosome to another. This is always unbalanced because it creates a genetic imbalance.

A third type is the Robertsonian translocation. This occurs when two non-homologous chromosomes attach at or near their centromeres. The centromere is the constricted region of a chromosome. This process results in one large metacentric chromosome and one very small chromosome. The small chromosome may be lost with little effect on the organism. In humans, this can result in a karyotype with only 45 chromosomes. This happens because two chromosomes have fused into one. This type of translocation can involve various combinations of acrocentric chromosomes.

Many biological processes can trigger these chromosomal changes. The initiating event is often a double-strand break in the DNA. One major player is the non-homologous end joining (NHEJ) pathway. This pathway is meant to repair DNA by reconnecting broken ends. However, if the machinery misreads sequences with similar homology, it may join the wrong ends. This error leads to deletions, insertions, or incorrect sequence joining. Another cause is the creation of AID translocations. This involves turning a cytosine nucleotide into a uracil nucleotide, creating a mismatch.

Scientists have a long history of discovering these mechanisms. In 1916, William R. B. Robertson documented a chromosomal fusion in grasshoppers. This discovery is now known as a Robertsonian translocation. In 1938, Karl Sax showed that X-ray irradiation could induce translocations in plant cells. During the 1940s, Barbara McClintock used maize to study the breakage–fusion–bridge cycle. A major breakthrough occurred in 1960 with the discovery of the Philadelphia chromosome. This was the first chromosomal abnormality linked to human cancer. In 1973, Janet Rowley proved this was a translocation between chromosomes 9 and 22.

Technological advances have greatly improved our ability to detect these events. In the 1970s, chromosome banding techniques like Q-banding and G-banding were introduced. These allowed for precise identification of chromosomes in a karyotype. In the early 1980s, fluorescence in situ hybridization (FISH) was developed. FISH uses fluorescent probes to label specific DNA sequences on chromosomes. This helped researchers map translocation breakpoints more effectively. In the 21st century, high-throughput DNA sequencing allows detection at single-nucleotide resolution. This has revealed many translocations in various cancers and genetic disorders.

Translocations can lead to specific medical conditions and syndromes. For example, Emanuel syndrome is a result of an unbalanced nonreciprocal translocation. A fragment from chromosome 11 moves to chromosome 22. This causes neurological and physical developmental disorders, including microcephaly. Robertsonian translocations involving chromosome 21 can lead to "translocation Down syndrome." This happens due to mis-segregation during gametogenesis. In humans, the most common Robertsonian translocation involves chromosomes 13 and 14. This occurs in approximately 0.97 out of every 1,000 newborns. Carriers of these translocations may face risks regarding fertility or miscarriages.