Lecture 3 - PLB 113 Lecture 3 II. Genome ORG & Gene...

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PLB 113 – Lecture 3 II. Genome ORG & Gene Express B. Genomes Consist of scDNA and repeated DNA C. How are single copy and repeated DNAs organized D. How many genes in genome? If 56% of 1 Kb genomic clones have repeated DNA, does this mean that 56% of the tomato genome consists of repeated DNA? NO. If 1Kb fragment contains both signal copy DNA and repeated DNA, entire 1Kb fragment will hybridize on the gel as a repeated DNA even though it will also hybridize with scDNA. Thus, 56% is the maximum amount of repeated DNA in the genome. Single/low copy DNA: = virtually all genes are in single copy DNA (almost every genes present in the plants as single copy DNA) = single copy DNA contains gene = not all single/low copy DNA is gene Repeated DNA: 1) rRNA gene: = genes that give rise to ribosomal RNA ( rRNA genes ) = rRNA are synthesized as 45S precursors 5' - 18S - 5.8 S - 28 S - 3' <= this represents a single gene → In the genome, rRNA are present as tandem repeated rRNA expresses one after another with same orientation and orient as a cluster →→→→→→→→ = the cluster of rRNA gene are in the nuclei Tandem repeat s occur in DNA when a pattern of two or more nucleotides is repeated and the repetitions are directly adjacent to each other. [1] = In mammals, the tandem repeated genes are histone gene. 2) satellite DNA = name came from the experiment using CsCl density gradient centrifugation - a technique used to isolate DNA - DNA has a given density, it would bend with the density gradient after centrifugation. - satellite DNA consists of small tandem repeats of sequences (15bp - 1000bp) = different density 3) Transposons - discovered by Barbara McClintock in corn (Clicker question 1) - there are different types of transposons Type 1 = retrotransposons - have certain classes of retrotransposons - have long terminal repeats at both ends (LTR) - LTR in plants is essential in determining the genome looks like. - retrotransposons cannot move outside of the cell.
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Lecture 3 - PLB 113 Lecture 3 II. Genome ORG &amp; Gene...

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