The Open Door Web Site
Molecular Genetics Index
The Chemical Nature if the Gene
Gene Mutations (aka Point Mutations)
Gene mutations are changes in the structure of the DNA which affect only one gene.
The antisense strand is the DNA strand which acts as the template for mRNA transcription.
Substitutions will only affect a single codon. Their effects may not be serious unless they affect an amino acid that is essential for the structure and function of the finished protein molecule (e.g. sickle cell anaemia).
Because the genetic code is degenerate it is possible for a mutation to have no effect on the phenotype. Changes in the third base of a codon often have no effect:
Some substitution mutations can, however, be disastrous:
Inversion mutations, like substitutions, only affect a small part of the gene:
Because the genetic code has no "punctuation" the reading frame is set at the beginning of the gene. One additional base will change the whole reading frame from that point on.
Removing a base from the gene has a similar effect to addition. It changes the reading frame downstream of the mutation.
Mutations of haemoglobin continued
The sense strand (coding strand) cDNA sequence of for beta haemoglobin
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