When the Regulation of Gene Expression Fails

When the control of gene expression fails, there can be serious consequences, such as death, birth defects, and cancer. Birth defects can result when the regulation of one or more genes important for development is lost. This often occurs because of a mutation, but it can also occur if the embryo or fetus is exposed to certain chemicals, such as alcohol. Mutations in the receptor for fibroblast growth factor, for instance, cause dwarfism. Cancer occurs when the regulation of genes that control growth and cell division, programmed cell death (apoptosis), and cell migration are lost. see also Alternative Splicing; Birth Defects; Development, Genetic Control of; Gene; Hormonal Regulation; Post-translational Control; Proteins; RNA Processing; Signal Transduction; Transcription; Transcription Factors.

Eric Aamodt

Bibliography

Alberts, Bruce, et al. Molecular Biology of the Cell, 4th ed. New York: Garland Science, 2002.

Lodish, Harvey, et al. Molecular Cell Biology, 4th ed. New York: W. H. Freeman, 2000.

Struhl, K. "Gene Regulation. A Paradigm for Precision." Science 293 (2001): 1054-1055.

Tjian, R. "Molecular Machines That Control Genes." Scientific American 272, no. 2 (1995): 54-61.

Gene Families

Gene families are groups of DNA segments that have evolved by common descent through duplication and divergence. They are multiple DNA segments that have evolved from one common ancestral DNA segment that has been copied and changed over millions of years.

The members of a gene family may include expressed genes as well as nonexpressed sequences. Such nonexpressed sequences include promoters, operators, transposable genetic elements, and pseudogenes, which are genes that are no longer functionally expressed.

Pseudogenes resemble other family members in their linear sequence of nucleotides. However, they usually either lack the signals that would allow them to be expressed or have significant deletions or rearrangements that prevent successful transcription or translation.

One well-studied gene family is that of the globins, shown in both Figures 1 and 2. The globin family contains many pseudogenes as well as many functional genes, including the genes coding for hemoglobins (a, ยก3, y, S).

Gene families vary enormously in size and number, ranging, in the human genome, from just a few copies of very closely related sequences to more than a half-million copies of Alu sequences, which are transposable genome the total genetic material in a cell or organism

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