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Horizontalgene transfer

The transfer of genetic information from one genome to another.

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Conjugation = transfer of DNA from one organism to another by means of a plasmid.

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Transformation = uptake of free DNA from the environment.

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Transduction = transfer of DNA from one organism to another by a bacteriophage.

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An organism into which genetic information from a different organism has been incorporated as a stable part of its genome is a transgenic organism.

Aeqorea victoriagreen fluorescent

protein (GFP) ANDi

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OrthoOrthology logy ParaParalogylogy XenoXenologylogy

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Horizontal gene transfer is suspected when there is a discrepancy between gene phylogeny and species phylogeny, in particular when the tree reflects geographical proximitygeographical proximity rather than phylogenetic affinityphylogenetic affinity.

9Aedes aegypti

Patchy phylogenetic distributionPatchy phylogenetic distribution

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nucleus cytoplasm(CuZn-SOD)

cyanobacteria+ chloroplast

(Fe-SOD)

bacteria +mitochondria(Mn-SOD)

SOD = superoxide dismutase

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Leiognathus daura

Photobacterium leiognathi(CuZnSOD)

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13Crown Gall Disease

14Agrobacterium tumefaciens

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Plant GenePlant Gene

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PP elements&

hybrid dysgenesis

PP MM

MargaretKidwell

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P elements were not found in any D. melanogaster strains collected before 1950, and collections made subsequently showed increasing frequencies of P with decreasing age.

North and South America Europe, Africa, Middle East

Australia, Far East

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Two hypotheses:

1. Most D. melanogaster strains in nature carry P elements, but they tend to lose them in the laboratory.

2. P elements were recently introduced into D. melanogaster populations in nature.

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The recent acquisition hypothesis is supported by:

1. P strains that have been monitored in the lab for ~15 y were never observed to lose P.

2. There is a geographical cline in the temporal appearance of P in nature.

3. There is evidence for horizontal gene transfer.

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Species tree P-element tree

23Drosophila willistoni

Drosophila melanogaster

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Proctolaelapsregalis

26Marilyn A. Houck

Conditions for horizontal P-element transfer:

(1) two Drosophila females from the donor and the recipient species must lay eggs in proximity to one another

(2) the recipient egg must be less than 3 hours old (< 512 cells)

(3) the germline of the recipient embryo must incorporate a complete copy of P

(4) the receiving embryo must survive the biting injuries

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type-C virogene

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Informational genes:Informational genes: Genes involved in Genes involved in replication, transcription, replication, transcription, reverse transcription, and reverse transcription, and translation.translation.

Operational genes:Operational genes: All others.All others.

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informational operationalThe complexity hypothesisThe complexity hypothesis

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Genes move within the Genes move within the genome and between genome and between genomes.genomes.

Genetic “Genetic “MutatisMutatis mutandismutandis.” .”

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PromiscuousPromiscuousDNADNA

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Mitochondrial-sequence Mitochondrial-sequence invasions into the nuclear invasions into the nuclear genomegenome

Einat Hazkani-Covo et al.

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NumtNumtss** ( (nuclear mitochondrial nuclear mitochondrial DNA sequencesDNA sequences) are a type of ) are a type of promiscuous DNA, i.e., promiscuous DNA, i.e., nuclear sequences of nuclear sequences of mitochondrial origin.mitochondrial origin.

**pronounced “new mights”pronounced “new mights”

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The transfer of functional genes from the mitochondria to the nucleus is thought to have has stopped in evolution after the emergence of animals (~1,000 MYA).

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The reason is thought to be the differences between the nuclear and mitochondrial genetic codes.

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The transfer of nonfunctional pieces of mitochondrial genetic information continues to this day.

NumtNumts have been found so far s have been found so far in 83 eukaryote species.in 83 eukaryote species.

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Most species whose genomes Most species whose genomes have been completely have been completely sequenced contain very fewsequenced contain very few numtnumtss.. Saccharomyces cerevisiaeSaccharomyces cerevisiae 1717 numts numtsCaenorhabditis elegansCaenorhabditis elegans 33 numts numtsDrosophila melanogasterDrosophila melanogaster 33 numts numtsPlasmodium falciparumPlasmodium falciparum 33 numts numts

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In the human genome we find In the human genome we find ~1,000~1,000 numt numtss

total length = 831 Kb total length = 831 Kb

~0.02% of the nuclear genome~0.02% of the nuclear genome

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Numts: Evolution’s misplaced witnesses

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Junk DNAJunk DNA

Domestic Imported