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