The Practical Importance of Extranuclear Genes

Mutations of mitochondrial genes have been found to cause a number of hereditary diseases in humans. Many of these mutations lead to defects in muscles, including the heart, and the nervous system. Because mitochondrial genes are found in nearly all eukaryotes, they are often used to trace the evolutionary history of organisms, including humans. Chloroplast genes are used for evolutionary studies in plants and algae. When organelle genes are inherited from only one parent, they can be used to trace the ancestry of individuals within a species without the complications caused by recombination between maternal and paternal genes.

Mitochondrial genes can also be used to trace the female ancestor of humans, while Y-chromosome genes can be used to trace male ancestors. In this way, differences between males and females in migration or patterns of reproduction can be detected. In addition, mitochondrial genes are used in studies of animal behavior to identify the parents of animals and birds and determine their social structure. Since the organelle genome is so highly simplified, mtDNA or cpDNA can be retrieved and analyzed from ancient or poorly preserved samples in which there would be no chance of retrieving a nuclear marker. see also Cell, Eukaryotic; Mitochondrial Diseases; Mitochondrial Genome; Molecular Anthropology; Plasmid; Prion.

C. William Birky, Jr.


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Inheritance Patterns

Inheritance patterns are the predictable patterns seen in the transmission of genes from one generation to the next, and their expression in the organism that possesses them. (A gene is said to be expressed when it is read by cellular mechanisms that result in the production of a protein.) While people have long noted that offspring resemble parents, the formal description of inheritance patterns began with Gregor Mendel, whose discoveries laid the foundation for the modern understanding of genetic inheritance.

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