The genomes of organisms are made up of DNA, while viral genomes can be made of DNA or RNA.
It is an alteration in the genetic material (the genome) of a cell, a living organism or a virus that is more or less permanent and that can be transmitted to the descendants of the cell or virus.
Genetic mutations can be classified in two main ways:
- Hereditary mutations: are inherited from a parent and are present throughout a person’s life in virtually every cell in the body.
- Acquired (or somatic) mutations: They occur at some point during a person’s life and are present only in certain cells, not in every cell of the body.
These changes can be caused by environmental factors, such as ultraviolet radiation from the sun, or they can occur due to a mistake, as DNA copies itself during cell division.
Mutations acquired in somatic cells (cells other than sperm and ovules) cannot be passed on to the next generation.
Genetic changes that are described as de novo (new) mutations can be inherited or somatic.
Genetic alterations that occur in more than 1 percent of the population are called polymorphisms. They are common enough to be considered a normal variation in DNA.
Polymorphisms are responsible for many of the normal differences between people, such as eye color, hair color, and blood type.
Although many polymorphisms do not have negative effects on a person’s health, some of these variations can influence the risk of developing certain disorders.
How can genetic mutations affect health and development?
To function properly, each cell depends on thousands of proteins to do its job in the right places and at the right times. Sometimes genetic mutations prevent one or more of these proteins from working properly.
By changing a gene’s instructions to make a protein, a mutation can cause the protein to malfunction or be missing altogether.
When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition.
A condition caused by mutations in one or more genes is called a genetic disorder .
In some cases, genetic mutations are so severe that they prevent an embryo from surviving until birth. These changes occur in genes that are essential for development, and often disrupt the development of an embryo in its early stages.
Because these mutations have very serious effects, they are incompatible with life.
It is important to note that genes themselves do not cause disease; genetic disorders are caused by mutations that cause a gene to work incorrectly.
For example, when people say that someone has “the gene for cystic fibrosis, ” they generally mean a mutated version of the CFTR gene, which causes the disease.
All people, including those without cystic fibrosis, have a version of the CFTR gene.
Do all genetic mutations affect health and development?
No, only a small percentage of mutations cause genetic disorders, most have no impact on health or development.
For example, some mutations alter the DNA sequence of a gene but do not change the function of the protein produced by the gene.
Often times, certain enzymes repair genetic mutations that could cause a genetic disorder before the gene is expressed and an altered protein is produced.
Each cell has a series of pathways through which enzymes recognize and repair errors in DNA.
Because DNA can be damaged or mutated in many ways, DNA repair is an important process by which the body protects itself from disease.
A very small percentage of all mutations actually have a positive effect. These mutations lead to new versions of proteins that help an individual better adapt to changes in their environment.
For example, a beneficial mutation could result in a protein that protects an individual and future generations from a new strain of bacteria.
Because a person’s genetic code can have a large number of mutations with no health effect, diagnosing genetic conditions can be difficult.
Sometimes genes thought to be related to a particular genetic condition have mutations, but it has not been determined whether these changes are involved in the development of the disease; These genetic changes are known as variants of unknown significance (VOUS) or (VUS).
Sometimes, mutations are not found in suspicious genes related to the disease, but the mutations are found in other genes whose relationship to a certain genetic condition is unknown. It is difficult to know if these variants are involved in the disease.
What types of genetic mutations are possible?
The DNA sequence of a gene can be altered in several ways. The types of mutations include:
Nonsense mutation: This type of mutation is a change in a DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene.
Nonsense mutation: A nonsense mutation is also a change in a DNA base pair. Instead of substituting one amino acid for another, however, the altered DNA sequence prematurely signals the cell to stop making a protein.
This type of mutation results in a shortened protein that may or may not work at all.
Insertion: modifies the number of DNA bases in a gene and adds a DNA fragment. As a result, you get a protein that may not work properly.
Deletion: A deletion changes the number of DNA bases by removing a piece of DNA. Removed DNA can alter the function of the resulting protein (s).
Duplication: occurs when a piece of DNA is abnormally copied one or more times.
Repeat expansion: nucleotide repeats are short DNA sequences that repeat several times in a row. An expansion repeat is a mutation that increases the number of times the short DNA sequence is repeated. This type of mutation can cause the resulting protein to malfunction.
Can a change in the number of genes affect health and development?
People have two copies of most genes, one copy inherited from each parent.
In some cases, however, the number of copies varies, which means that a person can be born with one, three, or more copies of particular genes.
Less often, one or more genes may be completely missing. This type of genetic difference is known as copy number variation (CNV).
These segments are large enough to include entire genes. Variation in gene copy number can influence gene activity and ultimately affect many body functions.
The researchers were surprised to learn that copy number variation represents a significant amount of genetic difference between people.
More than 10 percent of human DNA appears to contain these differences in gene copy number.
While much of this variation does not affect health or development, some differences likely influence a person’s risk of disease and response to certain medications.
Can changes in chromosome number affect health and development?
Human cells normally contain 23 pairs of chromosomes, for a total of 46 chromosomes in each cell.
A change in the number of chromosomes can cause problems with the growth, development, and function of body systems.
These changes can occur during the formation of reproductive cells (eggs and sperm), in early fetal development, or in any cells after birth.
A gain or loss of chromosomes from normal (46) is called aneuploidy.
A common form of aneuploidy is trisomy, or the presence of an extra chromosome in cells.
“Tri-” is Greek for “three”; People with trisomy have three copies of a particular chromosome in their cells instead of the normal two copies. Down syndrome is an example of a condition caused by trisomy.
People with Down syndrome generally have three copies of chromosome 21 in each cell, for a total of 47 chromosomes per cell.
Monosomy, or the loss of a chromosome in cells, is another type of aneuploidy.
“Mono-” is Greek for “one”; people with monosomy have one copy of a particular chromosome in their cells instead of the normal two copies. Turner syndrome is a condition caused by monosomy.
Women with Turner syndrome generally have only one copy of the X chromosome in each cell, for a total of 45 chromosomes per cell.
In rare cases, some cells end up with extra complete sets of chromosomes. Cells with an extra set of chromosomes, for a total of 69 chromosomes, are called triploids.
Cells with two extra sets of chromosomes, for a total of 92 chromosomes, are called tetraploids. A condition in which every cell in the body has an extra set of chromosomes. It is not compatible with life.
In some cases, a change in the number of chromosomes occurs only in certain cells.
When an individual has two or more populations of cells with a different chromosome composition, this situation is called chromosomal mosaicism.
Chromosomal mosaicism is caused by an error in cell division in cells other than eggs and sperm.
More commonly, some cells end up with an extra or missing chromosome (for a total of 45 or 47 chromosomes per cell), while other cells have the usual 46 chromosomes.
Mosaic Turner syndrome is an example of chromosomal mosaicism. In women with this condition, some cells have 45 chromosomes because they are missing a copy of the X chromosome, while others have the usual number of chromosomes.
Many cancer cells also have changes in the number of chromosomes. These changes are not inherited; They are produced in somatic cells during the formation or progression of a cancerous tumor.
Can changes in non-coding DNA affect health and development?
It is well established that changes in genes can alter the function of a protein in the body, which can cause health problems.
It is becoming clear that changes in regions of DNA that do not contain genes (noncoding DNA) can also lead to disease.
Many noncoding DNA regions play a role in controlling gene activity, determining when and where certain genes are turned on or off.
By altering these sequences, a mutation in the antisense DNA can cause a protein to be expressed in the wrong place or at the wrong time, or it can reduce or eliminate the expression of an important protein when needed.
Not all non-coding DNA changes have an impact on health, but those that alter the expression pattern of a protein that plays a critical role in the body can disrupt normal development or cause a health problem.
Mutations in noncoding DNA have been linked to developmental disorders such as the isolated Pierre Robin sequence, which is caused by changes in the enhancer elements that control the activity of the SOX9 gene.
Noncoding DNA mutations have also been associated with several types of cancer.
In addition to enhancer elements, these mutations can alter other regulatory elements, including promoters, isolators, and silencers.
Mutations in regions that provide instructions for making functional RNA molecules, such as non-coding transfer RNA, micro RNA, or long RNA, have also been implicated in the disease.
The same types of genetic changes that occur in genes or that alter the structure of chromosomes can affect health and development when they occur in non-coding DNA.
These mutations include changes in single DNA building blocks (point mutations), insertions, deletions, duplications, and translocations.
Noncoding DNA mutations can be inherited from a parent or acquired during a person’s lifetime.
Much is still unknown about how to identify the functional regions of noncoding DNA and the role these regions play.
As a result, it is difficult to link genetic changes in non-coding DNA to their effects on certain genes and health conditions.
The roles of noncoding DNA and the effects of genetic changes on it are growing areas of research.
Can changes in mitochondrial DNA affect health and development?
Mitochondria are structures within cells that convert energy from food into a form that cells can use.
Although most DNA is packaged on chromosomes within the nucleus, mitochondria also have a small amount of their own DNA (known as mitochondrial DNA).
In some cases, inherited changes in mitochondrial DNA can cause problems with the growth, development, and function of body systems.
These mutations disrupt the mitochondria’s ability to efficiently generate energy for the cell.
Conditions caused by mutations in mitochondrial DNA often involve multiple organ systems.
The effects of these conditions are most pronounced in energy-intensive organs and tissues (such as the heart, brain, and muscles).
Although the health consequences of inherited mitochondrial DNA mutations vary widely, frequently observed characteristics include:
- Muscle weakness and wasting.
- Movement problems
- Renal failure .
- Heart disease.
- Loss of intellectual functions (dementia).
- Hearing loss.
- Abnormalities that affect the eyes and vision.
Mitochondrial DNA is also prone to somatic mutations, which are not inherited.
Somatic mutations occur in the DNA of certain cells during a person’s life and are generally not passed on to future generations.
Because mitochondrial DNA has a limited ability to repair itself when damaged, these mutations tend to accumulate over time.
An accumulation of somatic mutations in mitochondrial DNA has been associated with some forms of cancer and an increased risk of certain age-related disorders, such as heart disease, Alzheimer’s disease, and Parkinson’s disease.
Additionally, research suggests that the progressive accumulation of these mutations over a person’s lifetime may play a role in the normal aging process.
How are genetic mutations involved in evolution?
Evolution is the process by which populations of organisms change over generations. Genetic variations underlie these changes.
Genetic variations can arise from genetic mutations or from genetic recombination (a normal process in which genetic material rearranges itself as a cell prepares to divide).
These variations often alter gene activity or protein function, which can introduce different characteristics into an organism.
If a trait is advantageous and helps the individual survive and reproduce, the genetic variation is more likely to pass to the next generation (a process known as natural selection).
Over time, as generations of individuals with the trait continue to reproduce, the advantageous trait becomes more and more common in a population, making the population different from the ancestral one.
Not all mutations lead to evolution. Only inherited mutations, which occur in eggs or sperm cells, can be passed on to future generations and potentially contribute to evolution.
Some mutations occur during a person’s life in only some of the body’s cells and are not inherited, so natural selection cannot play a role.
Also, many genetic changes have no impact on the function of a gene or protein and are not helpful or harmful. Furthermore, the environment in which a population of organisms lives is essential for the selection of traits.
Some differences introduced by mutations can help an organism survive in one environment but not another: for example, resistance to certain bacteria is only advantageous if it is found in a certain place and harms those who live there.
So why do some harmful traits, such as genetic diseases, persist in populations instead of being eliminated by natural selection?
There are several possible explanations, but in many cases, the answer is not clear.
For some conditions, such as the neurological condition Huntington’s disease, signs and symptoms do not appear until after a person has children, so the gene mutation can be passed on despite being harmful.
For other harmful traits, a phenomenon called reduced penetration, in which some individuals with a disease-associated mutation show no signs and symptoms of the condition, may also allow harmful genetic variations to be passed on to future generations.
For some conditions, having one mutated copy of a gene in each cell is advantageous, while having two mutated copies causes the disease.
The best-studied example of this phenomenon is sickle cell disease: having two mutated copies of the HBB gene in each cell results in the disease, but having only one copy provides some resistance to malaria.
This disease resistance helps explain why the mutations that cause sickle cell disease are still found in many populations, especially in areas where malaria is prevalent.