An Introduction
The mutation is a common but not so common word among people. Of course, doctors, biologics, biochemists, higher secondary biology students and all those who are in or know about this field will be knowing this term. This isn’t just a simple thing as it seems. Changes caused due to mutation has the power to change the world, for good and for bad. The mere alterations occurring in our DNA brings novel origins and discoveries which are beyond one's imagination. So without further delay, let’s look into mutation.
Mutation Meaning
Mutation definition Biology refers to a change in the nucleotide sequence of the genome of a living organism, virus, or extrachromosomal DNA. Viral genomes can be of DNA/RNA.
The change or alteration occurring in our DNA base sequences (A, C, G and T) is due to various environmental factors including Ultraviolet light and also due to errors caused when the DNA is copied.
RNA and both are types of nucleic acids, therefore, anything with RNA or DNA can have a mutation. It concludes that living organisms including animals, humans, plants, bacteria, fungi, protists and archaea can all have mutations. Also, viruses can have mutations. Many mutations are neutral in effect and can also be harmful as well as helpful in some manner (organisms can survive certain unfavorable conditions because of mutation).
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What is Mutation and The Causes of Mutation?
The central dogma of molecular genetics involves the conversion of DNA into RNA (through transcription) and protein synthesis (through translation). Mutations make the protein synthesis go wrong during translation or mistakes in DNA are present that result in abnormalities in bodies in the form of some diseases like sickle cell anemia. So, the causes of mutation can be any of the below-mentioned points.
Mutations can be inherited from parents to a child.
Mutations are spontaneous, eg- DNA replication errors (internal factor), environmental factors and completely random reasons.
External factors such as certain types of chemicals or excessive radiation also cause mutations to occur.
Types of Mutation
After knowing the mutation definition and causes of mutation, let’s learn about different mutations and their types.
1. Gene Mutations
DNA makes up genes and genes can code for proteins, influencing various traits. However, not all genes code for proteins and not all genes are turned on.
Therefore, when a mutation in DNA occurs, it means a change in one or more DNA bases takes place, then different proteins are produced which affect an organism’s traits.
Example: A fruit fly's DNA faces mutations; it may include-
Substitution which means the wrong base is matched;
Insertion which means an extra-base or other bases are added in;
Deletion can occur which means a base is removed. So, the three types of gene mutations are substitution, insertion and deletion.
Insertions and deletions, discussed above, are known to have the potential to be especially dangerous. This is because if we add a base or remove a base, all of a sudden, the number of total bases change and every base that is read in three, everything that is read afterwards insertion/deletion could be affected. This is called frameshift mutation and it leads to many amino acid changes.
2. Chromosomal Mutations
When mutations occur at the level of the chromosome, it is called chromosomal mutation. Chromosomes are made up of DNA and protein, are highly organized and have lots of genes on them. The human chromosome number is 46; 23 from an egg cell and 23 from a sperm cell. Similarly, the fruit fly has 8 chromosomes, 4 comes from an egg cell and 4 comes from the sperm cell.
Chromosomal Mutation Examples
Examples of chromosomal mutations are duplication, where extra copies of genes are generated.
Another is deletion, where some of the genetic material breaks off and inversion when a chromosome segment gets inverted (i.e. reversed) and put back on the chromosome.
The last one is translocation when a fragment from one chromosome breaks off and attaches to another chromosome.
During meiosis, in fruit flies and other animals, meiosis makes sperm and egg cells that can have half the number of chromosomes as the organism. And sometimes, those chromosomes don’t separate completely. It is called nondisjunction resulting in an egg or sperm cell that has too many or too few chromosomes.
Mutation can be passed down to an offspring; for example, a protist with mutation when undergoes asexual reproduction and division, the daughter cell can inherit the same mutation. These can be categorized as somatic mutations, which we will discuss later here.
Also, a fruit fly that reproduces sexually to pass a mutation to its offspring if that mutation is found in the genetic material of the sperm/egg cell. Frequent studies have been done to study fruit flies so these can be used to cite various examples for mutations.
Humans also pass down mutations to the offspring, for example, substitution occurring in the case of sickle cell anemia. Hemoglobin is a protein in your red blood cells that helps in carrying oxygen, however in sickle cell anemia, the gene coding for hemoglobin is mutated and if an offspring inherits two copies of this gene (one from each parent), it can have this disorder too. It is a condition where it is difficult for RBCs to carry oxygen because the shape of the RBC is affected by the mutated Hb protein. And in other cases, if an offspring gets one copy of a gene from one parent, it is only the carrier but not officially gets the disease.
3. Somatic Mutation
Here, the cell that has acquired genetic alteration passes it to the progeny of the mutated cell during the extensive and complicated process of cell division. The mutation is basically occurring in the somatic cells of a multicellular organism rather than the germinating cell, ie; the egg and the sperm. That is what makes it different. Somatic mutations result from environment changers like Ultraviolet radiations and several other chemicals and artificial substances. The mutation affects all the cells from the mutated cell. These mutations can occur in the major part of the body of an organism or plant. It may showcase the mutation, or it may not showcase the mutation. This causes many diseases including cancer.
Because these gets transferred through somatic cells only, the mutation will not be passed to the next generation through sexual reproduction. If the mutation is to be multiplied, the mutated cell has to either go through cell division, as said earlier, I should be cloned.
Some of the somatic mutation examples include navel oranges and red apples.
4. Germinal Mutation
In germinal mutation, the alteration in the germinal cells causes the mutation. Germ cells are the ones that give rise to gametes. So this mutation can be passed by sexual means. This can occur before fertilization and also during different stages of the zygote formation and its progression towards a child. If the mutation occurs before fertilization, then all the cells of that individual will be mutated. If the mutation occurs just after fertilization, it will be a gonosomal mutation. In the mutation developed sometime after fertilization, there will be a small set of cells either from germinating cells or somatic cells or both.
Genetic counselors work to help families that may be affected by genetic disorders; this cites the importance of studying mutations.
FAQs on Mutation - A Genetic Change
1. What is a mutation in biology?
A mutation is a permanent alteration in the nucleotide sequence of an organism's DNA (or RNA in some viruses). This change in the genetic material is the ultimate source of all genetic variation and can affect a single DNA base pair or a large segment of a chromosome. These changes can alter the genes, which in turn can lead to changes in the proteins produced and the organism's traits.
2. What are the main types of mutations?
Mutations are broadly classified into two main categories based on the scale of the genetic alteration:
- Gene Mutations: These are changes that occur within a single gene, often affecting one or a few nucleotides. They include point mutations (substitution of a single base) and frameshift mutations (insertion or deletion of one or more bases).
- Chromosomal Mutations: These are large-scale changes that affect the structure or number of entire chromosomes. Examples include deletion (loss of a chromosomal segment), duplication (repetition of a segment), inversion (reversal of a segment), and translocation (movement of a segment from one chromosome to another).
3. What is the difference between spontaneous and induced mutations?
The primary difference lies in their cause. Spontaneous mutations occur naturally due to errors during cellular processes like DNA replication or repair, without any external influence. In contrast, induced mutations are caused by exposure to external agents known as mutagens. These can include physical mutagens like UV radiation and X-rays, or chemical mutagens like those found in tobacco smoke.
4. What are some common examples of genetic mutations in humans?
A classic example of a gene mutation is Sickle-cell anaemia. It is caused by a single point mutation in the gene that codes for haemoglobin, leading to misshapen red blood cells. An example of a chromosomal mutation is Down's syndrome, which results from having an extra copy of chromosome 21 (Trisomy 21), leading to characteristic physical and developmental changes.
5. Are all mutations harmful and do they always cause a disease?
No, not all mutations are harmful. While many mutations are detrimental and can lead to genetic disorders, many others are neutral or even beneficial. A silent mutation, for example, is a change in the DNA sequence that does not result in a change in the amino acid sequence of the protein. Some mutations can be beneficial, providing an evolutionary advantage, such as the mutation that confers lactose tolerance in adults or antibiotic resistance in bacteria.
6. How does a frameshift mutation differ from a point mutation, and why is it often more severe?
A point mutation involves the substitution of a single nucleotide base, which might change only one amino acid in a protein or have no effect at all (silent mutation). In contrast, a frameshift mutation results from an insertion or deletion of one or more nucleotides. This is often more severe because the genetic code is read in triplets (codons). Adding or removing a base shifts the entire reading frame from that point onwards, altering every subsequent codon and leading to a completely different and usually non-functional protein.
7. What is the importance of a mutation being in a somatic cell versus a germline cell?
The importance lies in inheritability. A somatic mutation occurs in a regular body cell (like a skin or liver cell) and affects only the individual in which it occurs; it cannot be passed on to offspring. Cancers are often the result of accumulated somatic mutations. A germline mutation, however, occurs in a reproductive cell (sperm or egg). This type of mutation is significant because it can be inherited by the next generation, meaning every cell in the resulting offspring will carry the mutation.
8. Can a mutation ever be considered beneficial? Provide an example.
Yes, mutations can be beneficial and are a key driver of evolution. A beneficial mutation increases an organism's chances of survival and reproduction. A well-known example is the mutation causing the sickle-cell trait. While having two copies of the mutated gene causes sickle-cell anaemia, individuals with just one copy (heterozygotes) are healthy and show increased resistance to malaria, a significant advantage in regions where malaria is prevalent.
