In biology, a chromosomal mutation is the mutation of the chromosomal segments of the DNA strands. This can occur when the number of chromosomes or chromosome sets (ploidy) increases or decreases in a genome as well as when changes in chromosomes structure occur. Irregularities or accidents when cell division happens as well as during chromosomal crossing over or fertilization can all be causes of chromosomal mutation.
A chromosomal mutation is a mutation involving a long segment of DNA. These mutations can involve deletions, insertions, inversions, or translocations of sections or segments of DNA. In some cases, deleted portions may attach to other chromosomes, disrupting both the chromosomes losing the DNA and the one gaining it.
All types of chromosomes can undergo chromosomal mutation. Chromosomal mutation examples include chromosome deletion, duplication, inversion, and translation. These are known to cause different kinds of genetic and chromosomal mutation diseases.
For instance, chromosomal mutations on chromosome 4 have been investigated and proven to be the source of numerous genetic disorders and even cancer in humans. This includes conditions like narcolepsy and Parkinson’s disease.
Causes of Chromosomal Mutation
Usually, a chromosomal mutation happens because of a change in chromosome structures, chromosomal rearrangement, or other chromosomal abnormalities such as a change in chromosome number or missing chromosome. As previously stated, these often take place because there are issues during crossing over or cell division.
These cause different types of mutations in DNA. Sometimes, chromosomal parts are too slow during the anaphase of mitosis and this causes them to go off-track when the cell and nuclei are being rearranged.
When this transpires, the chromosomes may get digested by nucleases. On the other hand, some chromosome sets or segments might get duplicated by accident, creating a different type of mutation during cell division.
During cross-over, more types of genetic mutations occur as the chromosomes may break or separate abnormally causing cases of chromosomal disorders. Chromosomal aberration can also occur during nuclear cell division when the division is contorted and causes numerical mutation.
These usually happen throughout meiosis and can be artificially or naturally occurring. If the type of chromosomal mutation is present on a heredity gene, then this mutation will be passed down from generation to generation.
There may also be chromosomal mutations that are caused by radiation and chemical molecules. Mutagens can result in different consequences in organisms based on the cause, degree, and position of the chromosomal mutation.
Mechanism of Chromosomal Mutation
The way the chromosomal mutations work is all based on the type of mutation that occurs. Lagging or abnormal pairing of chromosomes can cause a difference in the number of chromosomes in a cell. These chromosomes are not separated during anaphase and cause the additional or misplacement of chromosomes.
Conversely, alternations in the chromosomal structure transpire when segments of chromosomes are digested and also occur when mistakes or accidents are made when the nucleus is being reorganized.
Types of Chromosomal Mutations
Most chromosomal mutations are either Chromosomal Mutations I or Chromosomal mutations II.
- Chromosomal Mutations I involve the processes of inversion, deletion, duplication/amplification or translocation
- Chromosomal Mutations II involves aneuploidy and polyploidy.
I. Chromosomal mutations I
As mentioned above, the four types of Chromosomal Mutations I are inversion, deletion, duplication/amplification, and translocation. All four of these can be seen in Figure 3 above. These mutations alter the structure of the chromosome since they tend to break and these pieces often form sticky ends.
A. Inversion
Inversion chromosomal mutation follows the rules of inversion biology. Just as the name implies, the chromosome is inversed, and its segments are reversed from end to end. A piece of the chromosome is removed then reattached but in the opposite direction than it was originally. When this does not include the center or the centromere of the chromosome, it is called paracentric inversion. When the inversion does include the centromere, it is pericentric.
DIAGRAM
Examples of inversion
Two well-known examples of inversion chromosomal mutations are the inversion of chromosome 12 creating the tallest teenager in the world. This inversion mutation is also seen in a species of Coelopa frigida insect. This mutation gives the insect a variety of physical attributes that usually occur in the smaller version of the organism rather than the larger.
B. Deletion
Also known as partial monosomies, these occur when a piece of a chromosome accidentally gets removed or deleted. There can be cases with one piece deleted at the end (terminal deletion), two deletions – one deleted within the chromosome, and one on the end – (interstitial deletion). Microdeletions also occur when the deletions in the chromosomes are too small to be detected.
DIAGRAM
Examples of Deletion
Cri-du-chat syndrome (condition as a result of a deletion of a piece of chromosome 5) and 22q11.2 deletion syndrome are examples of deletions that occur in the chromosomes.
- Cri-du-chat symptoms are named this way since infants who suffer from this condition often have a high-pitch cry similar to that of a cat.
- The microdeletion of chromosome 22 causes 22q11.2 deletion syndrome that often results in a variety of syndromes including heart problems, infections, and interesting facial features.
C. Duplication/Amplifications
As the name implies, an extra copy of a segment or the entire chromosome is present in the nucleus. These are also known as partial trisomies. Often an organism that usually has two copies of a chromosome will have three in the case of duplication. This can happen anywhere along the chromosome whether in the middle or on the ends.
DIAGRAM
Examples of Duplication/Amplifications
- When an extra copy of chromosome 22 is made, it results in 22q11.2 duplication syndrome. This autosomal dominant condition can often cause slow vertical growth, weak muscle tone, and intellectual disabilities.
- MECP2 duplication syndrome can also cause weak muscle tone as well as intellectual disabilities. This duplication mutation is often seen in males and is caused by the duplication of the MECP2 gene.
D. Translocation
Translocation chromosomal mutation follows the route of biological translocation. This happens when a segment of a chromosome breaks off and then relocates to a completely different chromosome. This creates fusion chromosomes as one type of chromosome fuses with another.
Reciprocal translocation occurs when pieces of chromosomes “swap” places. Robertsonian translocation occurs when a segment of a chromosome is attached to another chromosome, causing an elongation of it. These can be balanced or unbalanced, where the chromosome is fully functional with no missing genetic information (balanced) or with important missing pieces and cannot function as normal (unbalanced).
DIAGRAM
Examples of Translocation
- The translocation of chromosome 21 onto the 14th chromosome causes the common genetic mutation of down syndrome.
- This mutation is also the cause of many leukemias and lymphomas. For instance, a translocation between the 15th and 17th chromosomes causes Acute promyelocytic leukemia (APL) and translocation between the 12th and 15th OR the 1st and 12th chromosomes causes Acute myelogenous leukemia (AML).
II. Chromosomal Mutations II
The other type of chromosomal mutation categories Chromosomal mutations II than consists of aneuploidy and polyploidy. The general category of these is called heteroploidy since they cause a mutation by changing the number of chromosomes present in the cell.
A. Aneuploidy
This mutation either causes the loss or addition of a chromosome by the contortion of the chromosome set. Nondisjunction during meiosis or mitosis usually results in this mutation.
Examples of Aneuploidy
Down syndrome is also an example of aneuploidy. It is caused by the trisomy is the nondisjunction of chromosome 21. It usually causes mental retardation that can be mild or even severe.
B. Polyploidy
This mutation causes the creation of two sets of genomes within an organism. It is not usually common naturally however, it can be observed in some plants. It usually causes effects like giantism and the reduction of fertility.
Examples of Polyploidy
The “Doob” plant in South Asia undergoes this type of mutation being triploid and sterile. It can, however, be cultivated vegetatively.
The Advantages of Chromosomal Mutations
Often when one thinks of any type of mutation, they think of the negatives it may bring. However, in some cases, chromosomal mutations can benefit the organism.
Survival
Some mutations can help the organisms to survive better than others. Lactose tolerance became an advantage to have over others when numerous populations depended on cows and goats as sources of food.
We also see cases around the world where these chromosomal mutations have resulted in immunity to HIV, resistance to malaria (sickle cell), and even become physical advantages such as the height mutation in an Ecuadorian tribe.
Diversity
Chromosomal mutations are often what make us unique as living organisms. Physical features such as blue eyes, blonde hair, and even freckles were a result of chromosomal mutations, allowing humans to become more diverse in their appearance. Hair color, eye color, beauty spots and other features caused by these genetic mutations all promote variation among the human race.
The Disadvantages of Chromosomal Mutations
On the other hand, chromosomal mutations can be dangerous and even detrimental to the life of living organisms. Some of these can cause numerous problems within animals, plants, and humans.
Genetic Disorder
These are specific disorders or disabilities caused by mutations within the organism’s DNA. These can be small genetic issues that may barely affect the individual or larger issues that may bring major concerns to the individual. A chromosomal disorders list can be seen below:
- Trisomy 21: Down Syndrome
- Trisomy 18
- Trisomy 13
- Klinefelter Syndrome
- XYY Syndrome
- Turner Syndrome
- Triple X Syndrome
Other Diseases
Diseases like diabetes, cancer, and even asthma are all results of chromosomal mutations. These diseases can lead to serious health issues that can, in severe cases, cause death to the individual suffering from these conditions. For instance, sickle cell anemia is predisposed to persons of African/black descent.
Applications of Chromosomal Mutation
Depending on the branch of biology, mutations will have different applications. These include:
- Within molecular therapy, chromosomal mutations can be used as treatment and even cures for numerous kinds of diseases, both genetic and hereditary.
- Medicines as well as plant and animal breeding use chromosomal mutations at an applied level to carry out their work.
- Chromosomal mutations have been playing an essential part in the evolution and how genomes and chromosomes are changing for certain living organisms.
- Biological issues can be solved with the use of chromosomal mutations when they are designed and arranged in special ways.
- The use of Chromosome Mutation II in the form of polyploidy has created seedless fruits and vegetables.
