January 26, 2010

Gene Mutation

Introduction

            In the field of biology, mutations are changes to the genetic material (usually DNA or RNA).  Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during processes such as meiosis or hypermutation.  In multicellular organisms, mutations can be subdivided into germline mutations, which can be passed on to progeny and somatic mutations, which cannot be transmitted to progeny.  Mutations, when accidental, often lead to the malfunction or death of a cell and can cause cancer.  Mutations are considered the driving force of evolution, where less favorable (or deleterious) mutations are removed from the gene pool by natural selection, while more favorable (beneficial or advantageous) ones tend to accumulate.

 

Gene Mutation

 

            This is a permanent change in the DNA sequence that would make up a gene.  The gene mutations range in size from a single DNA building block, or DNA base, to a large segment of a chromosome.  This mutation in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene and consequently cause changes in the way a cell behaves.  It can alter in way that the sequence of each gene determines the amino acid sequence for the protein it encodes.  The DNA sequence is then interpreted in groups of three nucleotide bases, called codons.

 

            There are two ways in which gene mutations occur:

 

  1. They can be inherited from a parent. 

This is called hereditary mutations since it is passed from parent to child.  Similarly, it is also called germline mutations because they are present in the egg and sperm which are called germ cells.  This type of mutation is present throughout a person's life in practically every cell in the body.  However, De novo mutations (new mutations) may occur if mutations are only in an egg or sperm cell or those that occur just after fertilization.  It would explain genetic disorders in which an affected child has a mutation in every cell even though there no family history of the disorder has. 

 

  1. They can be acquired during a person's lifetime.

Acquired mutations or somatic mutations occur in the DNA of individual cells at some time during a person's life.  Changes could take place environmental factors such as ultraviolet radiation from the sun, or if a mistake is made as of DNA copies itself during cell division.  Ultraviolet light and other certain chemicals can damage DNA by altering nucleotides bases so that they look like other nucleotide bases.  Consequently, when the DNA strands are separated and copied, the altered base will pair with an incorrect base and cause a mutation.  Another way that such environmental agents cause mutation is by breaking the bonds between oxygen and phosphate groups for it will create a mutated form of the gene paving the way for a possibility that the mutated gene will produce a protein that functions differently.

 

            Furthermore, mutation may also occur through mistakes that are created during DNA duplication.  Although this situation is rare at about once in every 100,000,000 bases, mutation will still be a result when the DNA polymerase makes a mistake.  It is also called as somatic as it refers to cells other than sperm and egg cells which, conversely to that of inherited mutation, cannot be passed on to the next generation. 

 

In some instances, mutations will occur in a single cell within an early embryo.  During growth and development, the individual will have some cells with the mutation and some cells without the genetic change.  This condition is called mosaicism.  Genetic changes are either rare or common in the population.  A normal variation in the DNA which also occurs in more than 1 percent of the population is called polymorphism.  This variation is responsible for making the normal differences between people such as eye color, hair color, and blood type. 

 

 

 

How Will Gene Mutations Affect Health and Development?

 

            Each cell in our body depends on the proper job of thousands of protein just to function correctly.  As critical as it is, a simple involvement of gene mutation will deter one or more of these proteins from working appropriately.  Because mutation will change a gene's instructions for making a protein, it will accordingly cause protein malfunction if not missing entirely.  This protein malfunction will then disrupt the normal development in the body or cause a medical condition.  Such condition is called genetic disorder which is literally caused by mutations.  At some extent, gene mutations can even cause a severe damage to an embryo preventing it from surviving until birth.  These severe and serious effects of mutations are in contrary to life. 

 

            Significantly, genetic disorders are caused by mutations making a gene function improperly and not that genes themselves can cause disease.  Most of our diseases originally come from our genes.  However, mutations are neither harmful nor helpful (neutral mutation).  The harmfulness or helpfulness of mutations depends on the environment (Harter, 2003).  There would be undesirable and favorable mutations depending on the environment.  It is not simple to give examples of favorable or unfavorable mutations since it is not usually known as to what extent a trait is genetically fixed and to what extent it reflects a reaction to the environment.  Moreover, science hasn't known what genes will affect a specific trait.  Even so, a mutation may be favorable in the sense that it permits survival in an unfavorable environment and yet be unfavorable in a better environment. 

 

REFERENCES

 

Genetics Home Reference (2006 March). Your Guide to Understanding Genetic Conditions. Retrieved 21 March 2006, from http://ghr.nlm.nih.gov.

 

 

Genetic Science Learning Center. The University of Utah. How do Mutations Occur? Retrieved 21 March 2006, from http://gslc.genetics.utah.edu.

 

 

Harter, R. (2003 June). The Talk Origins Archive: Exploring the Creation/Evolution Controversy. Are Mutations Harmful? Retrieved 21 March 2006, from www.talkorigins.org.

 

 

Appendices

 

Nucleotide – one of the structural components, or building blocks, of DNA and RNA.  It consists of a base (one of four chemicals: adenine, thymine, guanine, and cytosine) plus a molecule of sugar and one of phosphoric acid.

 

Codons – these are three bases in a DNA or RNA sequence which specify a single amino acid. 


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