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Gene mutations

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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. ...read more.


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 tumour which may be benign and not affect other tissues, or malignant, which live parasitically on healthy cells, a condition known as cancer. The effects of gene mutation are extremely variable. Most minor gene mutations pass unnoticed in the phenotype since they are recessive, but there arc several cases where a change in a single base in the genetic code can have a profound effect on the phenotype. Sickle cell anaemia in humans is an example of base substitution mutation affecting a base in one of the genes involved in the production of hacmoglobin. ...read more.


Gene reshuffling as a result of crossing-over, independent assortment, random fertilisation and mutations, may increase the amount of continuous variation but the evolutionary implications of this are often short-lived since the changes produced may be rapidly diluted. Certain gene mutations, on the other hand, increase discontinuous variation and this has the more profound effect on changes in the population. Most gene mutations are recessive to the 'normal' allele which has come to form genetic equilibrium with the rest of the genotype and the environment as a result of successfully withstanding selection over many generations. Being recessive the mutant alleles may remain in the population for many generations until they come together in the homozygous condition and are expressed phenotypically. Occasionally a dominant mutant allele may arise in which case it will appear imniediately in the phenotype. ...read more.

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