 DNA- genetic material of eukaryotes.  Are highly variable in size and complexity.  About 3.3 billion bp in humans.  Complexity- due to non coding sequences which outweigh the coding sequences.  Eukaryotic chromosomes contains- unique, moderately repetitive and highly repetitive DNA.

 Unique DNA- DNA with unrepeated sequences.  Moderately repetitive- contains short sequences that are repeated times. Dispersed.  Highly repetitive-short sequences present 1000s of times(<100 bp).  Classified into interspersed genome repeats and tandem arrays. do not code for proteins or RNA.  Linked to major events in evolution.

Interspersed Repeats Transposons: Regions of the genome that can move from one place to another. Discovered by Barbara Mc Clintock. Two types: DNA transposons and retro transposons.

Transposons DNA transposonsRetro transposons AutonomousNon- autonomous

LTR RETRO TRANSPOSONS: Long terminal repeats retro transposons are similar to the genomes of retro viruses. Flanked by bp direct repeats. For jumping they require RNA pol RNA. Original DNA is maintained. RNA DNA Expand in number by duplication (Copy-Paste). Contains Long terminal repeats, gag, pol, eny, prt.

NON –LTR retro transposons. 1.LINE’s Autonomous Active elements belong to LINE 1 family. Contains 2 ORF’s ORF 1-Unknown ORF 2- contains reverse transcriptase and endonuclease. Trancriptase transported L1 DNA mRNA Cytoplasm and ORF 1 translated Translation proteins bind to mRNA Nucleus ORF 2 cuts DNA Reverse Transcriptase cDNA.

2.SINE’s  Non autonomous.  Derived from 2 types of genes.  <500 bp  Most abundant SINE in humans- Alu.  3’ ends has long stretch of adenine residues and flanked by 4-10 bp of direct repeats.

Functions  Cause mutation  Agents for genome evolution  Increases plasticity.  Ideal for genetic studies.  Act as “sign posts” for finding and mapping functional genes.  Diseases associated: Huntington’s chorea, myotonic muscular dystrophy, fragile X syndrome.

P element Present in D.melanogaster Used in mutagenesis and creation of Genetically Modified flies bp long Do not use RNA intermediate. Tranposition is controlled by repressors.

Tandem Arrays Made of successive identical or nearly identical repeat units. Vary in length. Larger repeats-satellites. Form arrays of 1000 – 10 million repeated units.

Functions Liable to undergo mis alignments during chromosome pairing. Highly polymorphic- DNA finger printing. Chromosome segregation. Study of populations. Construction of evolutionary tree. As markers in gene mapping. Evaluate specific genes in tumors.