Mutations
are the source of new alleles in a species. Mutations can be beneficial,
harmful, or have no effect. There are many types of mutations. The first type
of mutation is a point mutation. A point mutation changes only a singe base
pair. So if your DNA read ACTGTA a point mutation DNA would read ACTTTA, the highlighted T
is where your point mutation occurred. Point mutations occur because random
errors in DNA synthesis or random errors in the repair of damaged sites.
Replacement substitutions are a form of point mutation that results in an amino
acid change. On the other hand, point mutations that do not change the amino
acid are called silent substitutions. Amino acids are coded from the three base
pair codon, but some codons code for the same amino acid. For example if the
codon TAC codes for the amino acid leucine and TAT also codes for leucine. The
C to T point mutation would be a silent mutation since it codes for the same
amino acid. The Wobble Hypothesis states that the third base pair in an
anticodon can align in several ways to allow it to recognize more than one base
in the codons of mRNA. A second form of mutation is Transversion. A
transversion mutation occurs when a purine is substituted for a pyrimidine or
vise versa. A purine in DNA is either adenine or guanine. A pyrimidine is
cytosine, thymine, and in the case of RNA uracil. So if your DNA sequence read
ATCGAT the mutated strand would read AACGTA. The highlighted letters are where a transversion mutation
occurred. The pyrimidine thymine was replaced with a purine adenine. Another
type of mutation is a transition mutation. This is very similar to a
transversion mutation. In a transition mutation a purine is replaced with
another purine or a pyrimidine is replaced with another pyrimidine. If your
sequence read TAGCTATACG the mutated strand could read TAGTTATGCG. In your mutated
strand the pyrimidine cytosine was replaced with another pyrimidine thymine.
The purine adenine was replaced with another purine guanine. Insertions occur
when extra base pairs are added into the DNA. So for example your DNA reads
TAGTCG an insertion would be the highlighted area TAGGATTCG. A Deletion occurs when a section
of the DNA is deleted. So in the same strand, TAGTCG, a deletion would result
in the shortened strand of TAGG, where TC was deleted. Since DNA is read in
codons an insertion or deletion can change the whole meaning of DNA’s message.
So if your original strand read MAX WAS MAD the deletion of the first M would
make the sentence not understandable: AXW ASM AD. There are other possible
mutations but, all mutations have the ability to produce new phenotypes if they
change the gene product. A mutation can have the three effects on an
individual. In most cases it does not have an effect. Mutations create new
alleles which is necessary for natural selection to occur.
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