0.1 Basic principles of genetics  (Page 5/19)

Lecture 6. altered genes are mutations

The DNA sequences from two individuals of the same species are highly similar - differing by only about one nucleotide in 1,000. A mutation is, most simply, an alteration in a DNA sequence.  This change may or may not lead to a change in the protein coded by the gene.  A change that has no effect on protein sequence or function is termed a polymorphism and is a part of the normal variation present in the human genome.  Often, however, a change in a DNA sequence will result in the disruption of gene function that we term "Clinical Manifestations" in the Clinical Integration Model .  The altered protein that results from a mutation can disrupt the way a gene functions, and this can lead to clinical disease.  How these mutations manifest themselves depends on each individual's unique genetic endowment and interactions with their environment. 

Furthermore, the change may or may not be passed on to subsequent generations.  If, as in non-familial cancer, the mutation occurs in isolated somatic cells , it will not be passed on to subsequent generations.  Only those mutations occurring to the DNA in the gametes (egg or sperm) will potentially be passed on to offspring.  If the mutation is passed on to the offspring, they will carry this mutation in all of the cells in their body.  

Following is a brief review of different types of mutations:

Base pair substitution

Missense mutation

Nonsense mutation

Silent mutation

Frameshift mutation

Deletions, insertions, and duplications