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 Pseudogene Creation of a processed pseudogene.

  Duplication Speciation  TDTD TSTS  and  are said to be paralogous genes  species1 and  species2 are said to be orthologous genes Species 1 Species 2

Examples of Duplicated Genes

Fate of Duplicated Loci (1)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

All vertebrates but jawless fish have  and  H 1 : Two independent gene losses H 2 : Duplication Time of duplication may be estimated by observing the phylogenetic distribution of genes

Repeated Duplication Creates Gene Families

Globins are differentially expressed during development

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

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

Basic Unit of DNA

Nucleic acids are long chains of nucleotides

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

Nucleotide Bases Adenine Guanine Cytosine Thymine } } Purines Pyrimidines Complimentary

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

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

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

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

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

Example of RNA specifying gene :rDNA array 18S28S NTS ETS ITS-1 5.8S ITS-2 1 array in Tetrahymena 19,300 copies in Amphiuma 200 copies in Human

ITS NTSETS 18SITS 28SNTS 28S human chimp pygmy chimp gorilla aBamHI bHindI cBgIII dHpaI d d d d a a a a b b b b c c c c c c c c Arnheim, 1983