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 – 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 PMM PMM