Gene mutations

What is a gene mutation?

Sudden and spontaneous changes in phenotype, for which there are no conventional genetic explanations or any microscopic evidence of chromosomal mutation, can only be explained in terms of changes in gene structure. A gene mutation or point mutation (since it applies to a particular gene locus) is the result of a change in the nucleotide sequence of the DNA molecule in a particular region of the chromosome. Such a change in the base sequence of the gene is transmitted to mRNA during transcription and may result in a change in the amino acid sequence of the polypeptide chain produced from it during translation at the ribosomes.

Types of gene mutation

There are a variety of forms of gene mutation involving the addition, loss or rearrangement of bases in the gene. These mutations take the form of the duplication, insertion, deletion, inversion or substitution of bases. In all cases they change the nucleotide sequence and result in the formation of a modified polypeptide. For example, deletion causes a frame-shift.

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Consequences of gene mutations

Gene mutations occurring during gamete formation are transmitted to all the cells of the offspring and may be significant for the future of the species. Somatic gene mutations which arise in the organism are inherited only by those cells derived from the mutant cells by mitosis. Whilst they may affect that organism, they are lost on the death of the organism. Somatic mutations are probably very common and go unnoticed, hut in some cases they niay produce cells with an increased rate of growth and division. These cells may give rise to a ...

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