Biology  5/e   Raven/Johnson
	Student   Online Learning Center

Mutations have an affect, be it small or large, on biological processes. Mutations may occur spontaneously within the cell or may result from some form of intervention. Genes or chromosome segments may migrate. Nucleotides may alter their conformation. Errors occur in otherwise normal chromosome behavior. Mistakes occur in replication. All of these possibilities are simply imperfections in normal events.

Chromosomes may be altered by the outside factors, called mutagens. Replication failures may be caused by chemical agents. Chromosomes may be broken by free ions caused by ionizing radiations. Ultraviolet light may cause adjacent nucleotides to pair and interface with replication.

Cancer is a very important consequence of somatic mutation. Cancer is a cell or group of cells multiplying in an invasive manner outside the control of the organism’s regulatory mechanisms. There is no certainty of being able to avoid cancer. It is, however, prudent to maintain a life style and behavior that minimizes the mutagenic insult upon one's genes.

We tend to assume that once a genome is acquired from our parents, our genome is ours for life as stable strings of nucleotides. While this is true for a large number of genes, alteration of genomes occurs in both prokaryotic and eukaryotic organisms. Bacteria produce fragments of chromosomes that may remain separate from the source chromosome, region with it, or even be transferred to another bacterium. Bacteria can, in fact, transfer a copy of their own chromosome.

Eukaryotic organisms, too, have migratory segments of DNA that may spontaneously relocate. Many errors in a chromosome's behavior are corrected in eukaryotic organisms. Some attempts to correct errors result in alterations. Pairing of homologues may be imprecise and cause errors of commission or omission. That is, errors may result from attempts to correct the imprecision or errors may result from a failure to correct the flaw. Normal crossing-over or errors in crossing-over in gametic cell lives result in alteration of the genome for future generations. Some of the many kinds of genome modifications have small effects or no effects. Others are catastrophic. Somewhere between the extremes are enough functional variances to fuel the engine of evolution.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.