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Gene Mutation
from more than one codon. The correspondence between an amino acid and a specific codon is universal among all organisms, with few exceptions.
Genes need to be regulated so that the cell only creates the proteins it needs at any given point in time. The cell regulates its genes based on its external environment and its role within a multicellular organism. Gene expression can be regulated at several steps, from transcription to the post-translational modification of the protein.
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Most of the time, DNA replication is very accurate but mutations can occur. The error rate in eukaryotes is a low as 10-6 per nucleotide per replication but it is higher in viruses that have just RNA as their genetic material. Basically, with each generation, one to two mutations will occur. Most small mutations can be caused by the DNA replication process with either point mutations or frame-shift mutations. Larger mutations happen because of deletions or recombination errors occurring in a replication process or by big problems caused by chromosomal abnormalities.
DNA repair mechanisms can fail or can act abnormally, causing a genetic mutation to occur. The repair of the damage, even with the mutation, is more important to the organism’s survival than restoring an exact copy of the chromosome after replication.
When multiple different alleles are present in a population of the same species, it is called polymorphic. Most of the different alleles function the same but some alleles can give rise to a mutant allele that has a completely different phenotypic trait. The most common allele is referred to as the wild type allele, while less common alleles are called mutant alleles. The genetic variation of different alleles in a population is referred to as genetic drift.
Most mutations are completely neutral, having no particular effect on the organism’s phenotype. These are called silent mutations. Some mutations don’t even change the amino acid sequence because there are more codons than there are amino acids. Other mutations will change the amino acid sequence but don’t change the way the protein functions so it functions in a similar way to the wild type protein. Other mutations can be dangerous or lethal to the cell or organism and are taken out of circulation by natural selection. A very few mutations allow for a benefit to the offspring, which aid in the evolutionary process because these offspring are more likely and more able to pass on necessary survival traits.
Genes that have a recent common ancestor are called homologs. They share the same evolutionary ancestry but act slightly differently. A few genes will change the actual species but this is extremely rare. The degree of sequence similarity between homologous genes is known as the conserved sequence. Changes to most of the gene’s sequence don’t affect the proteins
