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Horizontal
gene transfer

The transfer of genetic information
from one genome to another.
1
Conjugation = transfer of
DNA from one organism to
another by means of a
plasmid.
2
Transformation = uptake of
free DNA from the
environment.
3
Transduction = transfer of
DNA from one organism to
another by a bacteriophage.
4
5
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 victoria
green fluorescent
protein (GFP)
ANDi
6
Orthology
Paralogy
Xenology
7
Horizontal gene transfer is suspected when there is a
discrepancy between gene phylogeny and species
phylogeny, in particular when the tree reflects
geographical proximity rather than phylogenetic affinity.
8
Patchy phylogenetic distribution
Aedes aegypti
9
nucleus
cytoplasm
(CuZn-SOD)
SOD = superoxide dismutase
cyanobacteria
+ chloroplast
(Fe-SOD)
bacteria +
mitochondria
(Mn-SOD)10
Leiognathus daura
Photobacterium leiognathi
(CuZnSOD)
11
12
Crown Gall Disease
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Agrobacterium tumefaciens
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Plant Gene
15
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P
M
P elements
&
hybrid dysgenesis
Margaret
Kidwell
17
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
18
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.
19
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.
20
21
Species tree
P-element tree
22
Drosophila melanogaster
23
Drosophila willistoni
24
Proctolaelaps
regalis
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Conditions for horizontal Pelement 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
Marilyn A. Houck
(4) the receiving embryo must survive
the biting injuries
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type-C virogene
27
28
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Informational genes:
Genes involved in
replication, transcription,
reverse transcription, and
translation.
Operational genes:
All others.
30
The complexity hypothesis
informational
operational
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Genes move within the
genome and between
genomes.
Genetic “Mutatis mutandis.”
32
Promiscuous
DNA
33
Einat Hazkani-Covo et al.
Mitochondrial-sequence
invasions into the nuclear
genome
34
Numts* (nuclear mitochondrial
DNA sequences) are a type of
promiscuous DNA, i.e.,
nuclear sequences of
mitochondrial origin.
*pronounced “new mights”
35
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).
36
The reason is thought to be the
differences between the nuclear
and mitochondrial genetic codes.
37
The transfer of nonfunctional
pieces of mitochondrial genetic
information continues to this day.
Numts have been found so far
in 83 eukaryote species.
38
Most species whose genomes
have been completely
sequenced contain very few
numts.
Saccharomyces cerevisiae
Caenorhabditis elegans
Drosophila melanogaster
Plasmodium falciparum
17 numts
3 numts
3 numts
3 numts
39
In the human genome we find
~1,000 numts
total length = 831 Kb
~0.02% of the nuclear genome
40
Numts: Evolution’s
misplaced witnesses
41
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Junk DNA
Domestic
Imported
43