110C Lec16 Euk Genome - Structure Recombination

110C Lec16 Euk Genome - Structure Recombination - BCH 110C...

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BCH 110C Lecture 16 Eukaryotic Genome Reading: Lodish 6th ed. Pages 150-154; Chapters 5.2-5.3; 6.1-6.3; 6.5; 24.3 Figures on slides 15 and 24 are taken from Molecular Biology of the Cell, Alberts et al., 5 th ed. (pp. 321, 313, and 1564, respectively)
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Genetic (DNA) recombination partially explains why we have so much “extra” DNA Genetic recombination is the physical rearrangement of parts of DNA molecules. It is divided into four general classes: 1. DNA Transposition – rapid movement of DNA sequences to new places in the genome, sometimes increasing the size of the genome 2. Homologous or general recombination - directed by homologous pairing of DNA sequences (e.g. during meiosis), leading to “accidental” duplication of DNA regions and an increase or decrease in genome size 3. Site-specific recombination - recombination of retroviruses or other newly created DNA sequences into new sites in the chromosome, increasing genome size 4. Unusual rearrangements - a broad class of recombination which is little understood. In the absence of recombination, the structure of chromosomes would be rigidly conserved (except for point mutations and insertions and deletion mutations), life would probably be safer but also unable to adapt to changing or different environments. Under these circumstances, life would soon cease to exist.
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FISH: Fluorescence in situ hybridization (in situ=Latin “In its proper position”) Repetitive DNA families have moved to new positions in the genome over “evolutionary time” The position of selected repetitive DNA families on human metaphase chromosomes detected using antibodies for specific DNA sequences linked to various florescent tags.
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Some DNA elements move to new positions in the genome “rapidly” so that the effects of this movement can be seen after a cell division or after meiosis.
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A Simplified Explanation For Jumping Genes And Their Effect On The Kernel Color Of Indian Corn D uring the development of a corn grain, a single fertilized cell undergoes many divisions, producing the final “body tissue” of the individual grain of corn. Grains of Indian corn come in different colors, such as purple, yellow and white. Sometimes the individual grains are purple with white streaks or mottling. This mottling defies Mendel's basic principles of genetics because the cells are all derived from one fertilization event (one starting cell), but the changing colors in the corn grain are due to rapid mutations in the cell color genes. The explanation for this phenomenon involves "jumping genes" or transposons, and earned Dr. Barbara McClintock the prestigious Nobel Prize in Medicine in 1983 for her life-long research on corn genetics. T ransposons are genes that can move from one location to another on a chromosome “rapidly”. In the pigmented aleurone layer of corn grains, the position of the moving transposons may inhibit or block pigment production in some cells. For example, if the transposon moves to a position adjacent to or in a pigment-producing gene, the cells are unable to produce the purple pigment. This results in white
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110C Lec16 Euk Genome - Structure Recombination - BCH 110C...

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