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Overview of the Respiratory System

Author(s): Nancy Moreno, PhD, Deanne Erdmann, MS, and Sonia Rahmati Clayton, PhD
Showing Results for: human Return to Presentation

The Molecular Basis of DNA Sequence Variations (IV)

Null mutations are mutations that result in the absence of a protein product from a gene. Null mutations be nonsense or frameshift mutations if these mutations occur very early in the coding sequence of a gene. Functionally, null mutations can also be mutations that occur in the promoter regions of genes and eliminate expression (transcription) of the gene.

The human genome also contains a number of repetitive elements or tandomly repeated sequences. These repeated sequences are spread throughout the genome and can vary in size from a few dozen base pairs in length to hundreds of base pairs in length. Some repetitive elements occur outside of the coding sequences of genes, and others occur within the coding sequences. The consequences of variability in the length of repetitive sequences depends upon their genetic location.