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Types of Genetic Mutations
The DNA strand contains instructions on how to make proteins. Every three “letters” code for a specific amino acid, such as TGC, ATC, GAT, TAG, and CTC. Many amino acids together compose a protein. For simplicity’s sake, to illustrate concepts with the DNA strand, we will use examples in English. Here is a segment illustrating DNA in three-letter words:
The car was red. The red car had one key.
The key has one eye and one tip.
Point Mutations
Point mutations are mutations where one letter changes on the DNA sequence. A point mutation in our example could cause “car” in the second sentence to be read “cat”:
The car was red. The red cat had one key.
The key has one eye and one tip.
With this point mutation, we lost the information for one word (car) as well as changed the meaning of the sentence. We did gain one word (cat), but we lost one word (car) and lost the meaning of one phrase. So the overall result was a loss of information.
But many times, point mutations won’t produce another word. Take for instance another point mutation, which changes “car” not to “cat” but to “caa”:
The car was red. The red caa had one key.
The key has one eye and one tip.
With this point mutation, we lost the information for one word (car) as well as the meaning. We did not gain any new words, and we lost one word and lost the meaning of one phrase. So again, the overall result of this point mutation was a loss of information, but even more so this time.
Point mutations can be very devastating. There is a children’s disease called Hutchinson-Gilford progeria syndrome (HGPS), or simply progeria. It was recently linked to a single point mutation. It is a mutation that causes children’s skin to age, their head to go bald at a very early age (prekindergarten), their bones to develop problems usually associated with the elderly, and their body size to remain very short (about one-half to two-thirds of normal height). Their body parts, including organs, age rapidly, which usually causes death at the average age of 13 years.2
Not all point mutations are as devastating, yet they still result in a loss of information. According to biophysicist Lee Spetner, “All point mutations that have been studied on the molecular level turn out to reduce the genetic information and not to increase it.”3
Inversion Mutations
An inversion mutation is a segment of DNA in a particular strand that reverses itself. An inversion mutation would be like taking the second sentence of our example and spelling it backwards:
The car was red. Yek eno dah rac der eht.
The key has one eye and one tip.
With inversion mutations, we can lose quite a bit of information. We lost several words from, and the meaning of, the second sentence. These mutations can cause serious problems to the organism. The bleeding disorder hemophilia A is caused by an inversion in the Factor VIII (F8) gene.
Insertion Mutations
An insertion mutation is a segment of DNA, whether a single base pair or an extensive length, that is inserted into the DNA strand. For this example, let’s copy a word from the second sentence and insert it into the third sentence:
The car was red. The red car had one key.
Had the key has one eye and one tip.
This insertion really didn’t help anything. In fact, the insertion is detrimental to the third sentence in that it makes the third sentence meaningless. So this copied word in the third sentence destroyed the combined meanings of the eight words in the third sentence. Insertions generally result in a protein that loses function.4
Deletion Mutations
A deletion mutation is a segment of DNA, whether a single base pair or an extensive length, that is deleted from the strand. This will be an obvious loss. In this instance, the second sentence will be deleted.
The car was red. The key has one eye and one tip.
The entire second sentence has been lost. Thus, we have lost its meaning as well as the words that were in the sentence. Some disorders from deletion mutations are facioscapulohumeral muscular dystrophy (FSHD) and spinal muscular atrophy.5
Frame Shift Mutations
There are two basic types of frame shift mutations: frame shift due to an insertion and frame shift due to a deletion. These mutations can be caused by an insertion or deletion of one or more letters not divisible by three, which causes an offset in the reading of the “letters” of the DNA.
If a mutation occurs where one or more letters are inserted, then the entire sentence can be off. If a t were inserted at the beginning of the second sentence, it would read like this:
The car was red. Tth ere dca rha don eke yth
eke yha son eey ean don eti p.
Four new words were produced (two of them twice): ere, don, eke and son. These 4 words were not part of the original phrase. However, we lost 14 words. Not only did we lose these words, but we also lost the meaning behind the words. We lost 14 words while gaining only 4 new ones.
Therefore, even though the DNA strand became longer and produced 4 words via a single insertion, it lost 14 other words. The overall effect was a loss of information.
A frame shift mutation can also occur by the deletion of one or more “letters.” If the first t in the second sentence is deleted, the letters shift to the left, and we get:
The car was red. Her edc arh ado nek eyt hek
eyh aso nee yea ndo net ip.
Five new words were produced: her, ado, nee, yea, and net. However, once again, we lost 14 words. So again, the overall effect was a loss of information, and the DNA strand became smaller due to this mutation.
Frame shift mutations are usually detrimental to the organism by causing the resulting protein to be nonfunctional.
This is just the basics of mutations at a genetic level.6
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