Chromosomal Mutations: Definition and Examples, Causes, Mechanism, Types

A mutation is a change in the DNA series of the genome of an organism. Chromosomal mutations are changes in the structure or number of chromosomes. These mutations in chromosomes can cause human genetic disorders. Chromosomal abnormalities like Down syndrome, Turner syndrome, and Klinefelter syndrome arise due to such mutations.

This Story also Contains

1. What Are Chromosomal Mutations?
2. Types Of Chromosomal Mutations
3. Structural Chromosomal Mutations
4. Numerical Chromosomal Mutations
5. Causes Of Chromosomal Mutations
6. Effects Of Chromosomal Mutations
7. The Recommended Video On Chromosomal Mutations:
8. MCQs on Chromosomal Mutations

Chromosomal mutations affect large segments of DNA within chromosomes. These mutations disrupt the normal gene interaction and can lead to chromosomal disorders. Mutagens are agents that cause mutations in DNA and chromosomes. They can lead to chromosomal mutations by damaging the structure of chromosomes. Common mutagens include radiation, chemicals, and certain viruses.

What Are Chromosomal Mutations?

Chromosomal mutations are structural alterations or changes in the number of chromosomes in the cell. In either case, it is an event of potentially significant impact on the organism's genetic material. Chromosomal mutations distort the structure of the genetic material and can cause many genetic disorders and diseases. The following are some reasons why chromosomal mutations should be studied:

• First, it facilitates the diagnosis and treatment of genetic disorders. Chromosomal abnormalities enable a medical specialist to treat and advise the affected individuals and their families.

• Secondly, knowledge of these mutations enables the development of targeted therapies such as gene therapy.

• Chromosomal mutation forms our understanding of evolutionary biology by introducing increased variation that affects the adaptation process in species.

• This will, in turn, be applied in the fields of biotechnology and agriculture, especially where better yields and livestock breeding are important.

Types Of Chromosomal Mutations

These are broadly classified into structural and numerical chromatid mutations based on the nature of the effect caused to the chromosome. Their knowledge is of importance in comprehending ways through which genetic alteration and chromosomal abnormalities appear.

1. Structural Mutations

2. Numerical Mutations

Structural Chromosomal Mutations

Structural chromosomal mutations refer to changes in the physical structure of chromosomes. These mutations occur when a chromosome breaks and reattaches incorrectly, altering the sequence or number of genes The structural chromosomal mutations are described below:

Deletion

Deletion is a chromosome mutation involving a segment of the chromosome, causing the loss of one or more genes. A good example of deletion mutations is the Cri-du-chat syndrome, a human brain disorder caused by the deletion of part of chromosome 5. Characteristics noted in this syndrome include intellectual disability and a unique cat-like cry in infants.

Duplication

Duplication is a process in which the segment of a chromosome duplicates and gets included in the genome, resulting in excess genetic material. An example is Charcot-Marie-Tooth disease which causes nerve damage and leads to muscle weakness.

Inversion

Inversion consists of a chromosome segment that has been reversed end to end. One of the famous examples is Hemophilia A. An inversion in the X chromosome interrupts the clotting factor VIII gene and causes serious bleeding disorders in it.

Translocation

Translocation is the transfer of one segment of one chromosome to another non-homologous chromosome. The Philadelphia chromosome is a well-known abnormality associated with this, which forms because of a translocation of parts of chromosomes 9 and 22.

Numerical Chromosomal Mutations

Numerical chromosomal mutations involve changes in the number of chromosomes within a cell. These mutations affect the overall chromosome count rather than their structure. These are described below:

Aneuploidy

Aneuploidy occurs when a cell possesses an abnormal count of chromosomes. This can be monosomy or trisomy. The former results from the loss of a chromosome, while the latter involves the presence of an extra chromosome.

Examples: The most common example is Down syndrome, in which there is an extra chromosome 21, hence called trisomy 21. In humans, this syndrome bestows typical features of the face, developmental delay, and several health problems.

Polyploidy

Polyploidy is when a cell contains more than two pairs of chromosomes. This condition occurs relatively frequently in plants but rarely in animals. One example is hexaploid wheat, containing six sets of chromosomes. Its high degree of redundancy allows for its diversity and originality and perhaps contributes to its value as an agricultural crop.

Causes Of Chromosomal Mutations

Chromosomal mutations can be produced by numerous factors that are generally classified as spontaneous and induced mutations. Knowing these causes is, therefore very important in understanding how variations or anomalies in genetic material come into being.

1. Spontaneous Mutations

Spontaneous mutations are naturally occurring changes in the sequence of DNA and arise independently of any external influence. The mutations may be because of errors in the replication of DNA, repair, or DNA recombination. For example, DNA polymerase itself—a copying enzyme—may make mistakes that sometimes circumvent the corrective machinery of the cell. These errors may accumulate with time, later leading to chromosomal mutations. The randomness of spontaneous mutation accounts for at least half the individual variation within a population.

2. Induced Mutations

Induced mutations are the result of exogenous factors that change the DNA sequence. Exogenous factors include environmental agents such as radiation and chemicals. For example, exposure to UV radiation from sunlight might form thymine dimers in the DNA molecule that leads to skin cancer. Similarly, chemical mutagens such as benzene (a gasoline additive) and some pesticides interact with DNA to cause structural changes. Lifestyle factors, such as smoking or diet, can also induce mutations. For instance, carcinogens in tobacco smoke may lead to lung cancer through induced mutations in critical genes controlling cell growth.

Effects Of Chromosomal Mutations

Chromosomal mutations can produce a wide array of consequences at the health level of individuals and the evolutionary trajectory of species. The impacts have to be understood at these levels to understand the wider implications of genetic change.

Impacts On Health

• Chromosomal mutations often lead to genetic disorders.

• Turner syndrome occurs due to monosomy X, causing infertility and developmental issues.

• Klinefelter syndrome is caused by an extra X chromosome in males, leading to low testosterone and infertility.

• Some cancers originate from chromosomal mutations like translocations.

• These mutations can cause birth defects and developmental delays.

Evolutionary Effects

• Chromosomal mutations contribute to evolution and speciation.

• They introduce new genetic variations in populations. Some mutations are beneficial, enhancing survival and reproduction.

• Polyploidy in plants increases size, strength, and stress resistance.

• Over time, these mutations can create new species by preventing gene flow between populations.

• Thus, chromosomal mutations are key drivers of evolutionary change.

The Recommended Video On Chromosomal Mutations:

MCQs on Chromosomal Mutations

Question: In the following questions, a statement of assertion (A) is followed by a statement of reason (R)

(1) If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark A

(2) If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark B

(3) If the Assertion is a true statement but the Reason is false, then mark C

(4) If both Assertion and Reason are false statements, then mark D

Assertion: Chromosomal mutations can result in structural changes to chromosomes.

Reason: Chromosomal mutations can involve alterations in the number or structure of chromosomes, which can lead to changes in the genetic material carried by an individual's cells. Structural chromosomal mutations involve changes in the physical structure of a chromosome, such as deletions, duplications, inversions, and translocations.

1. Both Assertion (A) and Reason (R) are true, and Reason (R) is a correct explanation of Assertion (A).

2. Both Assertion (A) and Reason (R) are true but Reason (R) is not a correct explanation of Assertion (A).

3. Assertion (A) is true and Reason (R) is false.

4. Assertion (A) is false and Reason (R) is true.

Answer: Chromosomal mutations can occur spontaneously during cell division, or they can be caused by exposure to certain environmental factors, such as radiation or chemicals. Structural chromosomal mutations can have a range of effects on an individual's health, depending on which genes are affected and how they are altered. For example, some structural mutations can cause genetic disorders or increase the risk of certain types of cancer.

Overall, the assertion is supported by the reason provided. Chromosomal mutations can result in structural changes to chromosomes, which can have significant effects on an individual's health and well-being.

Hence, the correct option is 1) Both Assertion (A) and Reason (R) are true, and Reason (R) is a correct explanation of Assertion (A).

Question: Which of the following types of structural chromosomal mutations involves the transfer of a segment of one chromosome to another chromosome?

1. Deletion

2. Duplication

3. Inversion

4. Translocation

Answer: Translocations are a type of structural chromosomal mutation that involves the transfer of a segment of one chromosome to another chromosome. Deletions involve the loss of a segment of a chromosome, duplications involve the presence of an extra segment of a chromosome, and inversions involve the reversal of a segment of a chromosome.

Hence, the correct answer is option 4)Translocation.

Question: The movement of a gene from one linkage group to another is called :

1. Translocation

2. Crossing over

3. Inversion

4. Duplication

Answer: Chromosomal aberrations refer to changes in the structure of chromosomes and can result in genetic disorders. The four main types are deletion, where a portion of the chromosome is lost; duplication, where a segment of the chromosome is repeated; translocation, where a part of one chromosome is transferred to another; and inversion, where a segment of the chromosome is reversed. These structural changes can disrupt gene function and lead to various health problems or developmental disorders in an organism.

Hence, the correct answer is option 1) Translocation.

Also Read:

• Practice more on Chromosomal Mutation

• Molecular Basis Of Mutation

• Types of Mutations