A mutation is defined as the sudden change in gene i.e. nucleotide sequences in DNA, which may be qualitative or quantitative change. This may or may not be inheritable. Mutations can occur naturally due to any mistake during karyokinesis or DNA replication, or may be induced due to the effect of carcinogens in DNA like UV light, X-ray, arsenic, viral infection, etc.
There are several schemes for the classification of mutation types. They can be autosomal or sex-chromosomal based on types of chromosome; spontaneous or induced based on the mode of origin; a point or chromosomal mutation based on the number of genes included, etc.
Similarly, based on the type of cells where mutation occurs it can be classified as “somatic mutation” and “germline mutation”.
What is Somatic Mutation?
Somatic mutation can be defined as any alteration in the genetic sequence of genes of the somatic cells. Simply, it is the type of mutation occurring in somatic cells. It occurs after the fertilization of gametes during an organism’s life cycle.
Somatic cells, also called body cells, are the diploid cells of the body. They include all the cells of the body except haploid gametes (germinal cells). Examples are skin cells, muscle cells, nerve cells, bone cells, etc.
Somatic mutation can be passed to all the progeny of the mutated cell during the cell division process, but they are not inheritable to offspring. It can occur during the development of a zygote; hence a child can be born with somatic mutation. It can be either naturally occurring (spontaneous) due to error during DNA replication or may be induced due to mutagens.
The most common example of somatic mutation is the occurrence of cancer cells in the life of a person.
Somatic Mutation Example: Development of Cancer
Cancer means excess and uncontrollable growth of the body’s cells and its rapid spread infiltrating and destroying the normal body cells. It can occur at any stage of life in any of the body cells or tissues or organs. Common types of cancer in humans are lungs, skin, prostate, stomach, liver, breast, cervical, blood, thyroid, etc.
Change in DNA of a cell due to somatic mutation is responsible for the development of most cancers. Cancer development can be classified into 3 stages; initiation (mutation in a cell due to carcinogens), rapid multiplication of the mutated cell forming a tumor, and progression (spread of the tumor in other body parts).
What is Germline Mutation?
Germline mutation can be defined as any alteration in the genetic sequence of genes of the germinal cells (gametes). Simply, it is the type of mutation occurring in germinal cells.
Germinal cells are the haploid cells that develop into gametes and fuse together to form diploid somatic cells. They are found and produced only in gonads and are responsible for sexual reproduction. Examples are; gonocytes, the male gamete (sperm), and female gamete (ovum).
Germline mutations are inheritable; hence it is passed on to the next generations. It occurs during meiotic division during the formation of gametes. They are responsible for genetic disorders, variations, and species evolution. It also can be either spontaneous or induced types. Mostly, it is due to spontaneous in origin.
Examples include Huntington’s disease, Hemophilia, 18-Trisomy, Down’s Syndrome, etc.
Germline Mutation Examples: Huntington’s disease
It is an inheritable disease causing progressive degeneration of nerve cells in the brain of that person. It reduces or seizes the functional abilities, mobility, cognitive and psychiatric ability of the patient.
It is caused by an abnormal gene, the HD gene in chromosome 4. This abnormal gene was formed in a certain individual due to mutation in his/her germ cell and has inherited to his/her progenies. The mutation had triggered excessive repeat of ‘CAG’ sequence in HD gene causing it 40 to 80 times more than in normal gene. This results in the production of malformed huntingtin protein that clumps in the brain and affects nerve cells.
Somatic Mutation vs. Germline Mutation (13 Differences)
| S.N. | Somatic Mutation | Germline Mutation |
| 1 | It is defined as any alteration in the genetic sequence of genes of the somatic cells. | It is defined as any alteration in the genetic sequence of genes of the germinal cells. |
| 2 | It is also called “acquired mutation” as it is acquired during an individual’s life. | It is also called “hereditary mutation” as it is passed to offspring. |
| 3 | It occurs in somatic or body cells. | It occurs in germ cells. |
| 4 | It is not inheritable. | It is inheritable. |
| 5 | It affects only mutated cells and their progeny. | It affects all the cells of the organism. |
| 6 | It can occur at any stage of the life cycle. | It occurs only during gametogenesis. |
| 7 | It plays no role in evolution. | It is the basis of evolution. |
| 8 | It does not cause genetic disorders but may cause cancer. | It is responsible for genetic disorders and also germline cancers. |
| 9 | It is finished along with the death of the individual. | It continues till the offspring of the individual breed and may result in separate sub-species. Hence it is genetically more important. |
| 10 | In most cases, they show observable effects. | In most cases, they are silent and don’t show detectable effects. |
| 11 | They can be treated or cured. | They can’t be treated or cured. |
| 12 | Mosaicism occurs. | Usually, mosaicism doesn’t occur. |
| 13 | Examples include cancers, tumor development, a neurodegenerative disorder, etc. | Examples include Hemophilia, Down’s Syndrome, 18-Trisomy, etc. |
References
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