Chromosomal mutations affect the entire structure of a chromosome, often causing significant effects on multiple genes. Types of mutations include fusion, inversion, insertion, and deletion. Researchers use genetic mapping and sequencing to identify mutations.
Chromosomes, which contain genetic information in the cells of many different organisms, can be mutated through a variety of different processes, often to the detriment of the mutated organism. A chromosomal mutation occurs at the chromosomal level, which means that the entire structural unit of the chromosome is altered in some way. A chromosomal mutation is often considered different from a gene mutation, where only a single gene on a chromosome is changed by a mutation. Chromosomal mutations occur on a larger scale affecting a significant portion of the entire chromosome, so many genes can be affected by a single mutation.
A chromosomal mutation is generally classified based on the particular structural change made to the chromosome or chromosomes. One type of mutation, for example, is a fusion; it occurs when two different chromosomes or chromosome segments fuse together into one. Researchers actually believe that the second human chromosome is a fusion of two chromosomes possessed by pre-human ancestors. Another type of chromosomal mutation is called an inversion and occurs when a segment of a chromosome is inverted. Inversions often cause no visible mutations to the organism, as all genetic information is usually intact and unaltered, although this is not always the case.
When a chromosomal mutation alters the number of copies of a particular gene in an organism’s genome, it is much more likely to cause a noticeable or significant effect on the organism. Common mutations of this form include insertions, which insert a new segment into a chromosome, and deletions, which remove a segment from the chromosome. Both of these types of chromosomal mutations cause a change in the copies of a gene or genes present. Overexpression or underexpression of a gene, both of which can result from such mutations, can both cause drastic effects on gene expression within an organism. In the white mutation in the fruit fly Drosophila melanogaster, for example, the inability to sufficiently express a gene that codes for eye pigmentation results in flies with white eyes.
Researchers have many different ways to identify a particular chromosomal mutation or gene mutation. Organisms with different genetic traits can be crossed in different combinations in order to develop a general “map” that suggests the location of a given mutation. Researchers can also sequence parts of the organism’s genome. Sequencing gives researchers a detailed view of an organism’s genetic information and its location on a chromosome.
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