Lect10_duplication

Lect10_duplication - Announcements Gene duplication,...

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1 Gene duplication, divergence of genes, and ‘Selfish’ genes Announcements • Exam 1 is Monday • Bring a photo ID, scantron (blue), pencil, (possibly a pen) • Room assignments: If your last name begins with – A – Cl go to 212 VEIHMEYER – Co – Gl go to 216 WELLMAN – Go – Z go to 123 SCI LEC Photo © Dr Julian Gutt and Alfred Wegener Institute Eight forms of the AFCP protein have been discovered so far, and all 8 are very similar …If they have a common ancestor, what is the most likely reason why all AFCP proteins are not identical? A. Drift has modified the base sequences in some AFCP genes. B. Some AFCP genes have mutations that allow them to perform better than others. C. Some AFCP genes have mutations that prevent them from performing their function. Proteins with similar sequences are called homologs Sequence X Sequence A Sequence B It is assumed that the two proteins are related by descent -- had a common ancestor. resembles (ancestral sequence) bacterium cytochrome cytochrome rat Similar or homologous genes Homologous genes can be found in different species About 500 “immortal genes” have been identified -- strongly conserved for over 3 billion years These genes are involved in decoding DNA and RNA Homologous genes are similar in function, shape (purifying selection) but less similar in DNA sequence (drift)
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2 One way to acquire a NEW gene is by DUPLICATION and DIVERGENCE of a pre-existing gene. So where do new genes come from? Gene duplications – another type of mutation A whole region of the chromosome is repeated Often the duplication is the result of errors during recombination Initially results in identical, redundant copies of the gene, in the same genome Gene duplications -- another type of mutation Sequences diverge due to drift, then selection for new function Sequence of one copy is conserved by selection for old function Result is the addition of a gene to genome Evolution of the human α -globin and β -globin gene families Ancestral globin gene αβ α β β α ζ ζ ψ ζ ψ α 2 ψ α 1 α 2 α 1 ψ θ G γ A γ ψ β β δ α -Globin gene family on chromosome 16 β -Globin gene family on chromosome 11 γ E v o lu t io n a r y im e Duplication of ancestral gene Mutation in both copies Transposition to different chromosomes Further duplications and mutations Why are homologs so similar even in very distantly-related organisms? a. Not enough time has elapsed since common ancestor for them to diverge b. Mutation rates are low because of repair and editing c. Genes for essential proteins are not subject to mutational change d. Mutations that made big changes were eliminated by selection.
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3 • Recall the Antarctic fishes that have an AFCP gene that produces an antifreeze protein?
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This note was uploaded on 03/08/2011 for the course BIS 2A taught by Professor Grossberg during the Fall '08 term at UC Davis.

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Lect10_duplication - Announcements Gene duplication,...

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