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Genomes & their evolution. Ch 21.4,5. 21.4 – Multicellular eukaryotes have much noncoding DNA & many multigene families. About 1.2% of the human genome is protein coding exons. - PowerPoint PPT Presentation
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Genomes & their evolution
Ch 21.4,5
About 1.2% of the human genome is protein coding exons.
In 9/2012, in papers in Nature, the ENCODE group has produced a stunning inventory of previously hidden switches, signals and sign posts embedded like runes throughout the entire length of human DNA.
21.4 – Multicellular eukaryotes have much noncoding DNA & many multigene families
DNA sequences – non coding
• Regulatory sequences• Repetitive DNA sequences– Tandem repeats– Interspersed repeats
Transposable elements
• Segments of DNA that can move from one place to another within an organism’s genome
• Movement is by a form of recombination
Transposons & Retrotransposons
• Retrotransposons – 40% of human genome• DNA Transposons – 3% of human genome
Both require transcription to work- can interrupt gene function- can introduce genetic variation, through rearrangment
Alu elements
• Transposable elements – family of related sequences
• About 10% of human genome
• 300 nt long, do not code for any proteins
Other repetitive DNA
• Simple sequence DNA – many copies of short tandem repeated sequences
• STR – short tandem repeat – 3% of human genome
Multigene families
• Many genes occur in multigene families- collections of identical or very similar genes
• Allow for many copies of the mRNA and protein
• i.e. family for rRNA molecules – identical genes - rRNA is final product
• i.e. globin families – non identical genes – produce proteins found in polypeptide subunits in hemoglobin.
21.5 Duplication, rearrangement & mutation contribute to genome evolution
• Errors in Meiosis and duplication of genes• Nondisjunction can result in polyploidy
Human & mouse chromosomes
• Unequal crossing over can lead to duplication of genes• Transposons are homologous in chromosomes, can get
duplicated
Transposons and evolution
• 3 ways Transposons may have contributed to the evolution of the genome
• Promote recombination between different chromosomes
• Disrupt genes or control elements• Carry genes or individual exons to new locations• http://www.youtube.com/watch?v=
9MPiRx3SPMM