Gene Mutation: Definition, Types, Characteristics, Effects

What is Gene Mutation: Definition, Types, Characteristics, Effects:

Gene Mutation Definition:

  • A sudden change occurs in gene or DNA sequence is known as gene mutation.
What is gene Mutation

What is Gene Mutation?

  • Genes contain the information necessary to build and maintain our bodies. Therefore, when the gene changes, the normal function of the body may not be maintained. 
  • A change in a gene is called a “mutation.” Even small mutations can make a big difference in how a gene works. 
  • Cancer is a disease caused by mutations in genes.
  • The body of a gene is a substance called DNA (deoxyribonucleic acid). DNA can be compared to a “character string” because it expresses genetic information by the arrangement of four types of substances represented by A (adenine), T (thymine), G (guanine), and C (cytosine). 
  • For some reason, DNA letters may be replaced (substitution), other letters may be inserted (insertion), or they may be omitted (deletion). 
  • As a result, genetic information is transmitted, and proteins that are supposed to be produced may not be produced, or may be produced at the wrong time or place. 
  • DNA changes do not always occur in individual nucleotide, and when changes occur over a wide range, the gene itself may increase (copy number abnormality) or other genes may join together (fusion).

History of Gene Mutation

  • Gene mutations were first discovered in Drosophila by TH Morgan in 1910. 
  • HJ Mahler in 1927, LJ Stadler in 1928 were the first to induce mutations in Drosophila and maize using X-rays. 
  • In 1947, C. Auerbach first used chemical mutagens to induce mutations in Drosophila with nitrogen mustard.
  • In 1959, E. Fritz proposed the base substitution theory of gene mutation, and 
  • In 1961, FHC Crick et al. proposed the frameshift mutation theory. 
  • With the development of molecular genetics and the emergence of DNA nucleotide sequence analysis and other technologies, the types of DNA molecular structure changes caused by gene mutations have been determined, including the molecular structure of some hot spots, and targeted mutagenesis has been possible. .

Classification of Gene Mutation

Genetic mutations can be broadly classified into two types: 

Congenital mutations

  • Genetic mutations can be congenital, inherited from parents, or acquired after birth. 
  • Congenital mutations are also called germline mutations. 
  • That’s because genetic mutations are present in germ cells (sperm and eggs needed to make offspring) and are passed from parent to offspring and from one generation to another generation. 
  • A fertilized egg, which consists of an egg cell and a sperm cell, inherits DNA from both parents. 
  • If there is a mutation in either DNA, it means that the fertilized egg, which is the first cell, will have a mutation, and the baby that is born after repeated cell division and growth will have mutations in all the cells of the whole body. 
Acquired Mutations:
  • Acquired mutations also known as somatic mutations are DNA mutations that occur during the course of human life. 
  • Somatic cells are cells other than sperm and eggs, and mutations that occur in somatic cells are not inherited in next generation.
  • Acquired mutations are often caused by accidental mistakes in DNA during cell division, when one cell divides into two. 
  • It can also be caused by environmental factors such as chemicals, radiation, viruses and toxins.
  • Mutations are constantly occurring in every cell of the body. 
  • However, all cells normally have the ability to recognize mutations and repair them before they are passed on to the next cell. 
  • However, if the cell’s DNA damage repair mechanism is broken or weakened, the repair ability may decline with age. As a result, over time, the mutations accumulate.

Types of Gene Mutation

The DNA sequences of genes change in many ways. Gene mutations have various effects on health, depending on the part where the mutation occurs and whether it changes the functions of proteins that are essential for life. According to the changes of bases, gene mutations can be generally divided into two categories: 

  1. Base Substitution Mutation/ Point Mutation.
  2. Frameshift Mutations

1. Base substitution mutation:
  • Refers to the mutation caused by the substitution of one base pair in a DNA molecule by another different base pair.
  • Base substitution mutation is also known as point mutation. 
  • Point mutations are divided into two forms: conversion and transversion. 
  • If one purine is replaced by another purine or one pyrimidine is replaced by another pyrimidine it is called a transition.
  • Mutations in which purines replace pyrimidines or pyrimidines replace purines are called transversions. 
  • Since there are four bases in the DNA molecule, four transitions and eight transversions are possible. 
  • In naturally occurring mutations, there are more transitions than transversions.
  • Base substitution mutation includes silent mutation, missense mutation and nonsense mutation.

A. Missense mutation

  • A mutation in gene in which one base pair in the DNA sequence of a gene is changed, and one of the amino acids that constitute the protein produced from that gene is replaced with another amino acid.
  • For example, the sixth position of human normal hemoglobin beta chain is glutamic acid, and its codon is GAA or GAG. 
  • If the second base A is replaced by U, it becomes GUA or GUG, and glutamic acid is replaced by valine. 
  • Instead, the abnormal hemoglobin HbS is formed, causing the individual to develop sickle cell anemia, resulting in a mutational effect. 
  • The result of missense mutation usually makes the polypeptide chain lose its original function, and many protein abnormalities are caused by missense mutation.

B. Nonsense mutation:

  • A nonsense mutation is also a single letter (one base pair) change in the DNA sequence of a gene. 
  • Instead of replacing one amino acid with another, this mutation stops protein synthesis at that point. 
  • As a result, proteins with nonsense mutations either do not function properly or do not function at all.
  • For example, when the G in the ATG in the DNA molecule is replaced by a T, the codon on the corresponding mRNA chain changes from UAC to UAA, thus stopping translation and shortening the peptide chain. 
  • This mutation affects the function of the protein or enzyme in most cases.

2. Frameshift mutation:

  • Frameshift mutations occur when the “reading frame” of a gene is altered by DNA insertions or deletions. 
  • The amino acid sequence of a protein is determined by sequentially reading groups of three letters in the base sequence of the gene. This part to be read is called the reading frame. 
  • The gene with frameshift mutation can change the amino acid sequence of the polypeptide chain when it is expressed, thus seriously affecting the structure and function of the protein or enzyme.
  • Most of the proteins that are made do not work. 
  • Insertions, deletions, and duplications can all lead to frameshift mutations.
  • It can cause abnormal genetic information after the locus. 
  • Acridine mutagens such as proflavin, acridine, and acridine orange can be inserted between adjacent base pairs of DNA molecules due to their relatively flat molecules. 
  • If inserted before DNA replication, it will cause an insertion of 1 base pair; if inserted during replication, it will cause a deletion of 1 base pair, both of which result in frameshift mutations.
  • Frameshift mutation includes in Insertion mutation, deletion mutation, duplication Mutation.

A. Insertion mutation:

  • An insertion is an addition of a piece of DNA that changes (increases) the number of bases. 
  • If a foreign DNA is inserted into the DNA of a gene, its structure will be destroyed and lead to mutation. 
  • Escherichia coli phage Mu-1 and some insertion sequences (IS) and transposons are genetic elements capable of shifting positions, and when they are transferred into a gene, they mutate the gene.
  • Proteins made from the inserted gene may not function properly.

B. Deletion Mutation:

  • A deletion is a change (reduction) in the number of bases resulting from the deletion of a portion of DNA. 
  • Small deletions can miss one to a few base pairs within a gene, while large deletions can miss an entire gene or several adjacent genes. 
  • Proteins made from deleted genes may not function properly.
  • Mutations caused by deletions do not undergo reversion. 
  • So strictly speaking, deletion should belong to chromosomal aberration.

C. Duplication Mutation:

  • Duplication is the abnormal copying of a piece of DNA one or more times. 
  • Duplications in genes can change the function of proteins made from them.

D. Repeat extension Mutation:

  • A short sequence of DNA that is repeated many times in a row is called a “nucleotide repeat”. 
  • For example, trinucleotide repeats are 3 base pairs, and tetranucleotide repeats are 4 base pairs. 
  • Repeat expansion is a mutation that increases the repeat number of nucleotide repeats. 
  • When repeat expansion occurs in a gene, it can alter the function of proteins made from it.

Characteristics Gene Mutation:

As an important source of biological variation, gene mutation has the following main characteristics:

  • Gene mutations are ubiquitous in the biological world. 
  • It occurs in all organisms including lower organisms, higher animals and plants, and Animals.
  • Gene mutations that occur under natural conditions are called natural mutations, and gene mutations that are induced under artificial conditions are called induced mutations.
  • Gene mutations can occur randomly. 
  • It can occur at any stage of ontogeny and in any cell of the organism. 
  • Gene mutations can occur in somatic cells as well as in germ cells. 
  • Mutations that occur in germ cells can be passed on directly to offspring through fertilization. 
  • Mutations that occur in somatic cells are generally not passed on to offspring.
Mutation Frequency
  • In the natural state, the frequency of gene mutation is very low for an organism. 
  • It is estimated that in higher organisms, only one germ cell will undergo gene mutation in about 100,000 to 100 million germ cells, and the mutation rate is 105-108. 
  • Different organisms have different gene mutation rates. 
  • For example, microorganisms such as bacteria and bacteriophages have lower mutation rates than higher animals. Different genes of the same organism have different mutation rates. 
  • Most genetic mutations are harmful to organisms, and since any organism is the product of a long-term evolutionary process, they have achieved a high degree of coordination with environmental conditions. 
  • For example, the vast majority of human genetic diseases are caused by genetic mutations, and these diseases pose a serious threat to human health.

Effects Of Mutation:

The effects of gene mutations on gene function are diverse. Some mutations change the function of the protein, and these mutations that change the function of the protein

Frequently Asked Questions on Gene Mutation:

What is a genetic mutation? What are the main types?

Answer: Gene mutation refers to a sudden, heritable variation in genomic DNA molecules. The main types of base substitution mutations, frameshift mutations, deletion mutations, insertion mutations.

  • Base substitution mutation: refers to the mutation caused by the substitution of one base pair in a DNA molecule by another different base pair, also known as point mutation.
  • Frameshift mutation: refers to a sequence in which a series of coding sequences after the insertion or loss site are misplaced when one or several (not a multiple of 3 or 3) base pairs are inserted or lost at a certain position in the DNA fragment. kind of mutation.
  • Deletion mutations: Genes can also be mutated due to the deletion of longer stretches of DNA.
  • Insertional mutation: If a foreign DNA is inserted into the DNA of a gene, its structure will be destroyed and lead to mutation.

What does genetic mutations mean?

Answer: The meaning of gene mutations in biology refers to changes in gene that exist in the cell nucleus. Gene mutations caused by changes in a single base, or the lack of, repeated and insertion of multiple bases. The cause can be the error of the replication of genetic genes during cell division, or the influence of chemicals, radiation or viruses.

When does the genetic mutation happen?

Answer: Gene mutations can occur in any period of development, usually during DNA replication or during cell division period.

Will gene mutations be inherited?

Answer: Yes, There are 2 copies of each gene, which is inherited from each parent. Sometimes, special mutations or changes of genes increase the risk of cancer.

How to detect gene mutations?

Answer: Common detection methods of gene mutation detection

  • Sequencing Method
  • Single -chain constituent heterogeneous polymorphism analysis technology.
  • Polymerase chain reaction.
  • Restricted fragment length polymorphism analysis technology.
  • Probe amplification blocking system.
  • High -efficiency liquid chromatography.
  • Micro number polymerase chain reaction

Where is the gene present?

Answer: The gene is present on the chromosomes, and the chromosomes exist in the nucleus. A chromosome contains hundreds to thousands of genes. Each normal human cell contains 23 pairs of chromosomes, with a total of 46 chromosomes.

What is the main genetic material of humans?

Answer: The Genetic Material of most organisms is DNA, so DNA is the main genetic material but in some viruses RNA act as a genetic material.

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