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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 Crossing over Between Daughter Strands Addition (duplication) Deletion (tandom duplications) Crossing over Between Daughter Strands Addition Deletion
Processed Pseudogene Creation of a processed pseudogene.
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
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
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
Point mutations generally arise during DNA synthesis or repair Error rate of DNA polymerases and the Efficiency of DNA repair are heritable traits.
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
In humans 35,000?? different proteins are specified by the simple linear arrangement of four bases The Watson-Crick Model of DNA
Nucleotide Bases Adenine Guanine Cytosine Thymine } Purines Complimentary } Pyrimidines
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
Classes of Gene • Protein-coding genes : transcribed and translated • RNA specifying genes : transcribed • Untranscribed genes
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
How does mRNA specify the amino acid sequence of the protein? Every three nucleotides forms a codon : each codon codes for an amino acid
Figure 4.3 The Genetic Code (Codons of mRNA) Note : different codons specify the same amino acid (i.e. Code is Degenerate)
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
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