Selfish DNA

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Selfish DNA

• Honors Genetics

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DNA Genes and the Rest

• Genic ( Gene containing portion of DNA) -
• Genes are viewed as ORFS Open Reading Frames
  These are determined by a start
• 3 TAC and a stop ATT5
• Genes account for 25 of our DNA
• In a gene there are coding regions
• Exons
• Between the Exons there are intervening sequences
  called Introns

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What is the product of a Gene ?

• Proteins All types such as transmembrane
  proteins , transport proteins, immune proteins,
  messenger proteins, enzymes, channels, toxins,
  developmental proteins
• ( hox), transcription factors, and many more
• RNAs m RNA ( intermediate in protein
  synthesis), t RNA required for protein synthesis,
  r RNA( ribosomal RNAs), RNAi, antisense RNAs,
  micro RNAs, snurps, spliceosome RNAs and many more

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ORF
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What is a Gene?
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Gene Expression
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Spliceosome editing the primary transcript
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Intron Borders
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DNA to Protein

• Only 1 of DNA actually defines the structure of
  genes and proteins
• Out of 46 chromosomes containing 30,00-50,000
  genes only 1 is actively engaged in keeping you
  alive

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Making a Protein

• http//www.johnkyrk.com/DNAtranslation.html

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Genes are grouped in islands on chromosomes

• Genes are in clusters on chromosomes
• What is between the space between the genes
  contains DNA that has survived through evolution
• It is believed to be the substance of mutations
  contributing to change in the change for both the
  positive and negative

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Genes were thought to be fixed in one location on
a chromosome

• 17q31.2

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Barbara McClintock discovered jumping genes

• Jumping genes are referred to as mobile
• They have the ability to change their position
  and jump from one chromosome to another
• Jumping genes are also called TRANSPOSONS

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The Original Jumping Genes
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Transposons

• 1) IS - insertion sequence. Inverted repeats
  transposase gene
• 2) Composite transposon. Two IS elements
  antibiotic resistance gene(s)
• 3) Noncomposite transposon. Inverted repeats
  transposase gene antibiotic resistance gene(s)

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Transposon Action
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Transposon structure
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Transposable elements and the new meaning of
mutation
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Retrotransposons

• Retrotransposons move by a "copy and paste"
  mechanism but in contrast to the transposons
  described above, the copy is made of RNA, not
  DNA.
• The RNA copies are then transcribed back into DNA
  using a reverse transcriptase and these are
  inserted into new locations in the genome.
• Many retrotransposons have long terminal repeats
  (LTRs) at their ends that may contain over 1000
  base pairs in each.
• Like DNA transposons, retrotransposons generate
  direct repeats at their new sites of insertion.
  In fact, it is the presence of these direct
  repeats that often is the clue that the
  intervening stretch of DNA arrived there by
  retrotransposition. About 40 of the entire human
  genome consists of retrotransposons.

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Sines ( Short Interspersed elements)

• SINEs are short DNA sequences (100400 base
  pairs) that represent reverse-transcribed RNA
• Alus - Thousands of our Alu elements occur in the
  introns of structural genes.

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Alu Action

• ALU elements have been accumulating in the human
  genome throughout primate evolution, reaching a
  copy number of over a million per genome.
  However, most of these Alu copies are not
  identical and can be classified into several
  subfamilies (reviewed in DEININGER and BATZER
  1993 ).
• These different subfamilies of Alu elements were
  generated once mutations occurred within the
  "master" or "source" gene that actively
  retroposed at different rates and time periods of
  primate evolution (DEININGER et al. 1992 ).
• Currently, the Alu retroposition rate is reduced
  by 100-fold from its peak early in primate
  evolution (SHEN et al. 1991 ). The vast majority
  of the Alu elements present in the human genome
  inserted before the radiation of extant humans
  and are therefore observed in all individuals in
  the human population.

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Microsatellites

• Studies show that microsatellites, tandem repeat
  sequences abundant in the genomes of higher
  eukaryotes, contain reiterating A-rich loci,
  which are involved in the higher-order
  organization of the chromatin
• Other studies have shown satellites consisting of
  about 1 million copies of a 221-bp tandem repeat
  unit has been localized in the centromeres of 58
  of the 64 horse chromosomes
• Many hundreds of studies have implicated
  mutations in satellites, minisatellites, and
  microsatellites, in diseases which show genetic
  linkage, including studies on Crohn's disease

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What is Selfish DNA?

• The theory that we creatures exist for the
  preservation of genes and are nothing more than
  their throwaway survival machines.
• Natural selection means the differential survival
  of the fittest
• Does natural selection choose the most fit
  individuals or the most fit genes?

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What are the characteristics of Selfish DNA?

• They have been called "junk" DNA and "selfish"
  DNA.
• "selfish" because their only function seems to
  make more copies of themselves and
• "junk" because there is no obvious benefit to
  their host.

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Some theories on Alus

• Some of these contain sequences that when
  transcribed into the primary transcript are
  recognized by the spliceosome.
• These can then be spliced into the mature mRNA
  creating a
• new exon, which will be transcribed into a new
  protein product.
• Alternative splicing can provide not only the new
  mRNA (and thus protein) but also the old.
• In this way, nature can try out new proteins
  without the risk of abandoning the tried-and-true
  old one.

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Alternative splicing

• http//www.exonhit.com/UserFiles/Image/epissage.sw
  f?PHPSESSIDotrsjha8drtbpuah7knuu4c394
• http//www.exonhit.com/index.php?page59

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Alternative Splicing
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