It is any change or error that occurs within the chromosome.
These errors can be attributed to any problem or deficiency that occurs during cellular processes, such as mitosis and meiosis.
Unlike genetic mutations that involve the alteration of a gene or a segment of DNA on the chromosome, chromosomal mutations occur and change the entire chromosome.
There are three types of chromosomal mutations, which are:
- Mutations in the structure of chromosomes.
- Mutations in the number of chromosomes.
- Mutations in the sex chromosomes.
Characteristics of the types of chromosomal mutations
Structural chromosomal mutations
This type of chromosome mutation usually happens during any mistake in cell division.
And it is when homologous chromosomes pair up, genes on chromosomes separate, genes inserted on the wrong chromosome, or genes or set of genes are completely lost on the chromosome.
Basically, structural chromosomal mutations are classified into four: deletion, duplication, inversion and translocation (or places of change).
Elimination: occurs when a part of the DNA is not duplicated or is lost during DNA replication. The size of this region can be a mere nucleotide or it can be as large as a complete chromosome.
Common disorders are: Cri du chat, Duchenne muscular dystrophy, Di George syndrome , among others.
Duplication: This type of mutation occurs when an extra copy of a region (or regions) in DNA is produced.
This duplicated region can be present in its normal location on the chromosome or sometimes located on other parts of the chromosomes or even on another chromosome.
This duplication can now supply additional material that has the ability to develop new functions.
Common disorders are: Charcot-Marie-Tooth disease type I.
Inversion: During inversion, a part of the chromosome is inverted and inserted back into the chromosome. There are basically two types of inversion: pericentric and paracentric.
During a pericentric inversion, the inversion spans the centromere of the chromosome.
On the other hand, during a paracentric inversion, it only involves the short or long arm of the chromosome and the point of inversion does not include the centromere.
Common disorders are: amniocentesis during the gestation process of pregnancy.
Translocation: occurs when a fragmented chromosome tends to join with a non-homologous chromosome. This newly formed segment breaks off the chromosome and moves to a new position on another chromosome.
The most common disorders are: XX male syndrome, Down syndrome, infertility, and cancer.
Chromosomal number mutations
Cremosomal number mutations include:
Aneuploidy: It is a type of mutation in the number of chromosomes in which the ploidy (number of chromosomes) of the new individual is different from its wild type.
This is typically the result of chromosome nondisjunction during mitosis or meiosis, thus producing offspring with extra or missing chromosomes.
The naming of aneuploid diseases is generally based on the number of chromosomes added or removed. For example, a monosomic individual (2n -1) only has one copy of one chromosome, rather than two.
Other variations of aneuploidy are trisomic (2n + 1), nullisomic (2n-2), and disomic (n + 1).
If the individual with polyploidy has three sets of haploid chromosomes, the condition is said to be triploid, while if he has four sets of haploid, the condition is said to be tetraploid.
Interestingly, polyploidy is a common phenomenon among plants, as well as certain groups of fish, salamanders, frogs, and leeches.
Advantages of chromosomal mutations
Random errors that occur during cell division can be beneficial to organisms. Some of them are listed below:
Survival: Mutations are very essential because they help some individuals in the population to adapt to their environment while maintaining their survival.
They are also an important force in evolution because they balance the frequency of alleles present in the population.
In humans, some successful mutations include malaria resistance , lactose tolerance, and atherosclerosis tolerance.
Diversity: mutations in chromosomes are closely connected with the diversity (not only genetic but also physical) of living organisms.
Ultimately, the close interactions between inherited mutations and environmental pressures generate diversity between species.
And clearly, without genetic diversity, some of the fundamental mechanisms of evolutionary change cannot operate.
Examples: Since some chromosomal mutations are harmless, humans acquire different colored eyes such as black, brown, gray, green, or blue.
Disadvantages of chromosomal mutations
Some mutations can also be quite harmful. The following are some of the more common disadvantages of chromosome mutations:
- Genetic disorder: Mutations in the chromosome can cause a wide variety of genetic disorders. While most genetic disorders are rare, the severity of the error in even a small portion of the chromosome can be very devastating.
- Other diseases: In addition to the inherited disorder, certain mutations in chromosomes can also cause other diseases, such as cancer of the lungs, breast and bladder.