length width crossability chromosome number phenotype genotype colour shape number ratio...
TRANSCRIPT
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length
width
crossability
chromosome number
phenotype genotype
colour shape
number
ratio
multivariate analysis
UPGMA
leaves
stems
hairs
venation
flowers
morphology
anatomy
secondary chemistryembryology
natural group
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parsimony
maximum likelihood
Bayesian inference
RAPDs
AFLPs
RFLPsbootstrap
chloroplast
mitochondrion
nucleus
gene
intronspacer
PCR
SNPs
microsatellites
SSRs
monophyletic
paraphyletic
F-statistics
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Types of DNAPlants have THREE genomes:1) Nucleus2) Chloroplast3) Mitochondrion
A
G
T
C
A T
GC
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Nuclear DNA
Large size, ca 10x106
kb in flowering plants Linear arrangement,
as chromosomes Inheritance biparental Recombination
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Chloroplast DNA Small, 120-220 kb Circular, usually with
inverted repeat No recombination Inheritance usually
maternal in angiosperms, paternal in gymnosperms
Constant gene order in all green plants.
rpl2
16S23S
rpl2
16S23S
rbcL
atpB
atpE
large single copy region
small scr
matK
psbA
trnH
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Mitochondrial DNAAnimal Plant
14-26 kb 150-2500kb
Circular, usually homogeneous among cells
Set of different-sized circles, which arise from processes that interconvert between mother circle & subgenomic circles
No recombination, inheritance maternal
No recombination, inheritance maternal
Mutation rates high at sequence level; substitutions
Rapid evolution in gene order but slower at sequence level (ca x100 slower than in animals)
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Main sources of DNA evidence
Control centres turn genes on & off
Genes single-copy multi-copy code for proteins
Inter-genic spacers non-coding
sequences between genes
Introns non-coding
sequences within genes
List
eria
Sacc
haro
myc
es
Arabi
dops
is
Droso
phila
Homo
sapi
ens
020406080
100
Non-coding Coding
transposons & retroviruses
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Gene structure
• Exons are composed of start, amino acid & stop codons.
• Highly conserved regions.
• Useful at higher taxonomic levels, e.g. genus & above.
• Introns are non-coding regions within a gene.
• Spacers are non-coding regions between genes.
• Both potentially highly variable regions.
• Useful at genus level and below, sometimes down to population level.
upstream enhancer promot
er
TATA box
5’ UTR
3’ UTR
exon 1
exon 2
exon 3
intron 1
intron 2
spacer
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Multi-copy genes: rDNA
Tandem repeats: 100s to 1000s of copies. Nuclear genome: biparental inheritance.
sometimes problem with concerted evolution. Coding regions (nS) highly conserved
18S gene of soyabean shares 75% nucleotide homology with yeast.
ITS & IGS regions highly variable.
25S 25S18S
5.8S
IGS ITS1 ITS2
18S
IGS
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Making inferences from the data
Gene trees vs species or organism trees often only two genes (or regions)
studied [out of ca 25,000 genes present]
Data from the different genomes may or may not be congruent each genome tells its own story, which
may not be that of the whole organism
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ApproachesPhylogeny reconstruction, systematics Sequencing
Genepool & population level phenomena RFLPs ‘Fingerprinting’
RAPDs AFLPs
Microsatellites Allozymes (protein products of genes)
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Sequence: electropherogram
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Phylogenetic systematics parsimony. Identifies tree with minimium
number of mutations (character-state changes). maximum likelihood. Identifies tree that has the
highest probability of producing the observed data, given a particular model of evolution.
Bayesian inference. Like maximum likelihood but much more sophisticated. Hurts the brain!
ALL TREES CAN BE TESTED STATISTICALLY!!! bootstrap jacknife decay index
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st 0.447
st 0.555
st 0.468
st 0.390
st 0.287
st 0.289
Genepool & population phenomena
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RFLPsRestriction Fragment Length
Polymorphisms Use restriction enzymes to cut DNA at
recognition sites (usually 6b long). Separate fragments on an agarose gel. Stain fragments with ethidium bromide &
view with UV.
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Fragment patterns in hybrids
Different patterns are the result of gains/losses of restriction sites or inversions.
Co-dominant in nuclear DNA: good for detecting hybrids.
enzyme 1
enzyme 2
probe
7 12
4 5 9
enzyme 1 fragments AA AB BB
19 --- ---
12 --- ---
7 --- ---
enzyme 2 fragments AA AB BB
14 --- ---
9 --- ---
5 --- ---4 --- --- ---
nuclear DNA
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RAPDRandomly Amplified Polymorphic DNA
arbitrary 10bp primers target sequences flanked by inverted repeat primer sites
permits multiple annealing throughout all three genomes
coding & non-coding regions; single- & multi-copy DNA
inherited as a dominant (cannot distinguish htz from hmz)
indiv A
indiv B
gelA B
-- --
--
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AFLPsAmplified Fragment Length Polymorphsims
cut DNA with pair of enzymes: one rare cutter & one common cutter
attach known DNA sequences to the products
amplify products using the known sequences as priming sites
rather like RAPDs but much more reproducible
dominant inheritance
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Microsatellites(SSRs: Simple Sequence Repeats)
Short (1-6bp), tandem repeats (10-50 copies)
Mono- to tetra-nucleotides, e.g. (AT)n Random distribution assumed Primers designed for conserved flanking
regions Variation in repeat number
polymorphism Co-dominant inheritance
GAGAGAGAGAGAGA
(GA)7
GAGAGAGAGA
(GA)5
pri. flanking
pri. flanking
flanking pri.
flanking pri.
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SummaryType of study Type of DNA Preferred marker
Gene diversity & breeding system
nrDNA co-dominant markers: microsats, allozymes
Genotype diversity, clonality, individuality
nrDNA high resolution markers: microsats, RAPDs, AFLPs
Population structure & gene flow
nr or cp/mt DNA all
Phylogeography (gene-pool structure)
cp/mt DNA sequences, RFLPs
Speciation nr + cp/mt DNA all
Inter-specific hybridisation
nr + cp/mt DNA microsats, allozymes, RFLPs, AFLPs
Systematics (above sp. level)
nr + cp/mt DNA sequences, (AFLPs)