somatic and germ-line mutations:
DNA is composed of a double helix structure, each side of which is composed of a long string of nucleotides. Each nucleotide consists of a deoxyribose group, phosphate group and a nitrogenous base. Each group of three bases is code for an amino acid that is used to build proteins. A change in one of these bases is referred to as a point mutation. It could alter the protein, have no effect at all or stop it from being produced, depending on what that particular group codes for. It may result in an alteration in the DNA of a particular gene, causing the protein for which it codes for to not be produced or to change in some way. This change in DNA is referred to as a gene mutation. There are two types of gene mutations: somatic and germ-line.
Somatic mutations are those that occur in the cells of the body, therefore only affecting the individual that possesses the cells. Each time that this body cell containing the mutation duplicates, it passes on this mutation to its daughter cells. However, it does not affect the reproductive cells as once the person dies, the mutation is lost. Somatic cell mutation is heavily responsible for cancerous growths in the body that may be derived from the influence of a mutagen. They occur randomly, at any moment during a person's life.
Germ-line mutations occur when the reproductive cells of an individual are affected by the mutation. Thus, it can only occur in gametes and can therefore be passed onto an individual's offspring. However, the individual in which the mutation originally occurred is usually unaffected, but instead produces gametes with the affected DNA. If one of these altered gametes is used during fertilization, the mutation is passed on and can thus cause severe genetic defects, such as those associated with the disorder phenylketonuria (PKU).
Common forms of gene mutations include:
- Missense mutation - when a change in a base pair of DNA causes the substitution of an amino acid in the protein made by a gene.
- Nonsense mutation - when a change in a base pair of DNA signals for the cell to stop synthesizing a protein prematurely. This results in a malformed protein which may not function or may have an impeded function.
- Insertion - when a piece of DNA is added, changing the number of DNA bases. This results in an abnormal protein, which may not function properly.
- Deletion - when a piece of DNA is "deleted", thus resulting in a change in the number of DNA bases. They can remove as little as one base pair, or as many as entire neighbouring genes. This therefore alters the function of the proteins that these genes make.
- Duplication - when a section of DNA is copied more than once, altering the function of the resultant protein.
- Frameshift mutation - when the addition or lack of a DNA base causes a change in the codon of a gene. It shifts the grouping of these bases, thus changing the code for the amino acid to be produced. The protein synthesized according to this new code is normally non-functional.
Most gene mutations result in a recessive allele, which prevents the gene from being able to synthesise protein that would be of use to the body. Therefore, a person is able to possess a large number of mutations and be unaware and unaffected by them. However, if a person reproduced with a partner that had the same recessive mutations, then the condition could appear in their offspring, such is the case with disorders like cystic fibrosis. Some of these recessive allele mutations can be quite lethal if they are not masked by a normal allele. They can cause death to an embryo or foetus, or even result in the early death of a child.
Somatic mutations are those that occur in the cells of the body, therefore only affecting the individual that possesses the cells. Each time that this body cell containing the mutation duplicates, it passes on this mutation to its daughter cells. However, it does not affect the reproductive cells as once the person dies, the mutation is lost. Somatic cell mutation is heavily responsible for cancerous growths in the body that may be derived from the influence of a mutagen. They occur randomly, at any moment during a person's life.
Germ-line mutations occur when the reproductive cells of an individual are affected by the mutation. Thus, it can only occur in gametes and can therefore be passed onto an individual's offspring. However, the individual in which the mutation originally occurred is usually unaffected, but instead produces gametes with the affected DNA. If one of these altered gametes is used during fertilization, the mutation is passed on and can thus cause severe genetic defects, such as those associated with the disorder phenylketonuria (PKU).
Common forms of gene mutations include:
- Missense mutation - when a change in a base pair of DNA causes the substitution of an amino acid in the protein made by a gene.
- Nonsense mutation - when a change in a base pair of DNA signals for the cell to stop synthesizing a protein prematurely. This results in a malformed protein which may not function or may have an impeded function.
- Insertion - when a piece of DNA is added, changing the number of DNA bases. This results in an abnormal protein, which may not function properly.
- Deletion - when a piece of DNA is "deleted", thus resulting in a change in the number of DNA bases. They can remove as little as one base pair, or as many as entire neighbouring genes. This therefore alters the function of the proteins that these genes make.
- Duplication - when a section of DNA is copied more than once, altering the function of the resultant protein.
- Frameshift mutation - when the addition or lack of a DNA base causes a change in the codon of a gene. It shifts the grouping of these bases, thus changing the code for the amino acid to be produced. The protein synthesized according to this new code is normally non-functional.
Most gene mutations result in a recessive allele, which prevents the gene from being able to synthesise protein that would be of use to the body. Therefore, a person is able to possess a large number of mutations and be unaware and unaffected by them. However, if a person reproduced with a partner that had the same recessive mutations, then the condition could appear in their offspring, such is the case with disorders like cystic fibrosis. Some of these recessive allele mutations can be quite lethal if they are not masked by a normal allele. They can cause death to an embryo or foetus, or even result in the early death of a child.