nov 15 - 1 Handout- Extranuclear inheritance in eukaryotes...

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Unformatted text preview: 1 Handout- Extranuclear inheritance in eukaryotes November 15, 2006 In eukaryotes the transmission of traits between generations is dominated by the nuclear genes. However, a small subset of genes ( e.g. 1 in a 1000 for humans) is located on the chromosomes of cytoplasmic organelles mitochondria and plastids, as typified by chloroplasts. Mitochondria are a universal feature of eukaryotes, and chloroplasts are present in the cells of plants, algae, and some protists. These extranuclear genes are organized somewhat differently than the nuclear DNA, and as a consequence they show patterns of inheritance that do not obey Mendels laws. Because cpDNA and mtDNA are generally inherited maternally, comparisons of the base sequences in organelle DNA of different organisms can provide complementary evolutionary information to studies of nuclear DNA. We have also become interested in mtDNA mutations associated with human disorders. Learning Goals Mitochondrial and chloroplast genomes are relatively small; they each contain only a few dozen genes, typically located on a single chromosome; and they are present in hundreds or thousands of copies per cell. Review the Endosymbiotic Theory for the evolutionary origin of mitochondria and chloroplasts. What features of mitochondrial and chloroplast genetics support this theory? A mitochondrion is composed of hundreds of different RNAs and protein, yet its own genome only contains a few dozen genes. How is this possible? Many mitochondrial proteins are encoded by nuclear geneshow did this evolve? Why is the genotype of a mitochondrial gene potentially more variable than that of a nuclear gene? What is the meaning of the terms homoplasmic and heteroplasmic? When is the mitochondrial genome replicated, and how is it subdivided between daughter cells at mitosis? If a cell is heteroplasmic and undergoes mitosis, will its daughter cells have the exact same mitochondrial genotype? If a zygote (= fertilized egg) is heteroplasmic, will the cells of the adult produced that zygote have the same mitochondrial genotype? Mitochondrial inheritance in humans is typical of that in most animal species, i.e. the mother contributes ~99.9% and the father ~0.1% of the offsprings mitochondrial DNA. Why is this contribution so heavily biased towards the mother? How can a mother produce different offspring who carry variable percentages of mutant alleles for a mitochondrial gene? In eukaryotic cells, the vast majority of DNA is stored in the nucleus ....
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This note was uploaded on 02/22/2010 for the course BIO 51980 taught by Professor Buskirk during the Fall '06 term at University of Texas at Austin.

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nov 15 - 1 Handout- Extranuclear inheritance in eukaryotes...

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