chromosomal MUTATIONS:
Chromosomal mutations are those which affect a number of genes through the complete or partial involvement of the chromosome. They usually result in symptoms that are much more severe than those caused by gene mutations. The effects are usually so severe, that miscarriage often occurs in early pregnancy. There are many different types of chromosomal mutations:
- Deletion - when extra base pairs are lost from the DNA. The number of base pairs lost is highly variable; however, those that involve only one or two base pairs can have devastating consequences as they result in the creation of new "stop" codons, resulting in an underdeveloped protein. Those that involve three base pairs or more are less serious because they do not affect the "start" or "stop" codons.
- Duplication - when a part of the genetic coding occurs more than once. It may simply be the result of a chromatid breaking off and rejoining the wrong chromosome. It occurs during meiosis, and results in one gene with extra genetic material and another gene which lacks genetic material.
- Inversion - when a piece of chromosome breaks off, but ends up joining the chromosome again. However, it flips before it does so, thus scrambling the genetic code and affecting the ability of the chromosome to pair up during meiosis.
- Translocation - when a part of a chromosome breaks off and rejoins a different chromosome. They can be balanced, and result in no loss of genetic information (part of intron), or can be unbalanced, and result in the loss of genetic information (part of an exon).
- Non-disjunction - when during meiosis, a chromosome pair/chromatid did not separate properly, causing one daughter cell to have excess genetic information and one daughter cell to lack genetic information. Common types include: trisomy, monosomy, partial trisomy and partial monosomy.
- Isochromosome - when a chromosome has two identical arms instead of one long arm and one short arm. This is caused by extra copies of some genes being made, while other genes failed to be duplicated.
- Dicentric chromosome - when a chromosome contains two centromeres instead of one, often resulting in the loss of genetic information.
- Ring chromosome - when a chromosome breaks in two different places and the ends of the arms of the chromosome fuse together, creating a ring. The genetic information near the ends of the chromosomes are lost as a result.
- Deletion - when extra base pairs are lost from the DNA. The number of base pairs lost is highly variable; however, those that involve only one or two base pairs can have devastating consequences as they result in the creation of new "stop" codons, resulting in an underdeveloped protein. Those that involve three base pairs or more are less serious because they do not affect the "start" or "stop" codons.
- Duplication - when a part of the genetic coding occurs more than once. It may simply be the result of a chromatid breaking off and rejoining the wrong chromosome. It occurs during meiosis, and results in one gene with extra genetic material and another gene which lacks genetic material.
- Inversion - when a piece of chromosome breaks off, but ends up joining the chromosome again. However, it flips before it does so, thus scrambling the genetic code and affecting the ability of the chromosome to pair up during meiosis.
- Translocation - when a part of a chromosome breaks off and rejoins a different chromosome. They can be balanced, and result in no loss of genetic information (part of intron), or can be unbalanced, and result in the loss of genetic information (part of an exon).
- Non-disjunction - when during meiosis, a chromosome pair/chromatid did not separate properly, causing one daughter cell to have excess genetic information and one daughter cell to lack genetic information. Common types include: trisomy, monosomy, partial trisomy and partial monosomy.
- Isochromosome - when a chromosome has two identical arms instead of one long arm and one short arm. This is caused by extra copies of some genes being made, while other genes failed to be duplicated.
- Dicentric chromosome - when a chromosome contains two centromeres instead of one, often resulting in the loss of genetic information.
- Ring chromosome - when a chromosome breaks in two different places and the ends of the arms of the chromosome fuse together, creating a ring. The genetic information near the ends of the chromosomes are lost as a result.