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Primary Mechanism of Duplication : Unequal Crossing Over

Primary Mechanism of Duplication : Unequal Crossing Over. Crossing over Between Daughter Strands. Addition (duplication). Deletion. (tandom duplications). Crossing over Between Daughter Strands. Addition. Deletion. Polyploidization : complete genome duplication. Processed

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Primary Mechanism of Duplication : Unequal Crossing Over

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  1. Primary Mechanism of Duplication : Unequal Crossing Over Crossing over Between Daughter Strands Addition (duplication) Deletion (tandom duplications) Crossing over Between Daughter Strands Addition Deletion

  2. Polyploidization : complete genome duplication

  3. Processed Pseudogene Creation of a processed pseudogene.

  4. a Duplication TD a b Speciation TS a b a b Species 2 Species 1 aandbare said to be paralogous genes aspecies1andaspecies2are said to be orthologous genes

  5. Examples of Duplicated Genes

  6. Fate of Duplicated Loci • Both copies retain original function e.g. rRNA genes (2) Gain new function through mutation and selection e.g. globin genes (3) Become functionless pseudogenes e.g globin genes

  7. Time of duplication may be estimated by observing the phylogenetic distribution of genes All vertebrates but jawless fish have a and b H1: Two independent gene losses H2: Duplication

  8. Repeated Duplication Creates Gene Families

  9. Globins are differentially expressed during development

  10. Point mutations generally arise during DNA synthesis or repair Error rate of DNA polymerases and the Efficiency of DNA repair are heritable traits.

  11. Locus A Many different genes (loci) per chromosome Locus B Locus C Different forms of a gene are called alleles Chromosomes, Genes, and Alleles Traits are determined to a great extent by genes

  12. Basic Unit of DNA

  13. Nucleic acids are long chains of nucleotides

  14. In humans 35,000?? different proteins are specified by the simple linear arrangement of four bases The Watson-Crick Model of DNA

  15. Nucleotide Bases Adenine Guanine Cytosine Thymine } Purines Complimentary } Pyrimidines

  16. C T T G | | | | 3’ OH---dR---P---dR---P---dR---P---dR---P 5’ Schematic Representation of DNA G A A C 5’ P---dR---P---dR---P---dR---P---dR---OH 3’ | | | | G A A C

  17. Classes of Gene • Protein-coding genes : transcribed and translated • RNA specifying genes : transcribed • Untranscribed genes

  18. Schematic of Eukaryotic Protein-Coding Locus 5’ UTR 3’ UTR Intron 2 Intron 1 5’ 3’ Exon 1 Exon 2 Ex 3 GT AG GT AG Regulatory Sequences Initiation codon Stop codon

  19. How does mRNA specify the amino acid sequence of the protein? Every three nucleotides forms a codon : each codon codes for an amino acid

  20. Figure 4.3 The Genetic Code (Codons of mRNA) Note : different codons specify the same amino acid (i.e. Code is Degenerate)

  21. Example of RNA specifying gene :rDNA array NTS 18S 28S ITS-1 ITS-2 ETS 5.8S 1 array in Tetrahymena 19,300 copies in Amphiuma 200 copies in Human

  22. 28S ITS NTS ETS 18S ITS 28S NTS c b a d c 28S human a d b c c 28S chimp a d b c c 28S pygmy chimp a d c b c 28S gorilla a BamHI b HindI c BgIII d HpaI Arnheim, 1983

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