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John Brookfield Ecology Club 11 th February 2010.

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Presentation on theme: "John Brookfield Ecology Club 11 th February 2010."— Presentation transcript:

1 John Brookfield Ecology Club 11 th February 2010

2  Circular DNAs derived from bacterial symbionts  16kb, 37 genes (in humans)  Rapid evolutionary rates in warm blooded vertebrates (particularly in “D loop”)  Maternally transmitted and non-recombining

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4 2Nf

5 * * * * * * * * * * * * * * * * *

6 Nor Nor Nor Nor Sou Sou Sou Sou

7 Animals from Northern and Southern Populations (complete migration and mixing) Sou Nor Sou Nor Sou Nor Sou Nor

8 Nor Nor Nor Nor Nor Sou Sou Sou Sou Sou MRCA

9  Hardy-Weinberg Formula: q=1-p  AA: p 2  Aa: 2pq  aa: q 2 Random Mating Inbreeding (specified by F ), when homozygotes exceed p 2 +q 2

10 p=0.8 q=0.2 p=0.2 q=0.8

11  F ST =(p 1 -p 2 ) 2 /4(p(1-p))  -scaled squared difference in allele frequency between the populations  -averaged over alleles and loci

12 p=0.8 q=0.2 p=0.2 q=0.8 F ST = (0.8-0.2) 2 /(4x0.5x0.5)=0.36

13 What does F ST mean  F ST =(p 1 -p 2 ) 2 /4(p(1-p)) =(0.8-0.2) 2 /(4x0.5X0.5)=0.36 How many heterozygotes expected (Hardy- Weinberg)=2p(1-p)=0.50 How many seen= 2p 1 (1-p 1 )/2 +2p 2 (1-p 2 )/2 =0.8x0.2+0.2x0.8 =0.32

14 p=0.9 q=0.1 p=0.1 q=0.9 F ST = (0.9-0.1) 2 /(4x0.5x0.5)=0.64

15 p=1.0 q=0.0 p=0.0 q=1.0 F ST = (1.0-0.0) 2 /(4x0.5x0.5)=1.00

16 p=0.6 q=0.4 p=0.4 q=0.6 F ST = (0.6-0.4) 2 /(4x0.5x0.5)=0.04

17 pA=0.6 qa=0.4 pB=0.7 qb=0.3 pA=0.4 qa=0.6 pB=0.3 qb=0.7 Linkage Disequilibrium: Association of A and B and association of a and b

18 The Island Model: F ST =1/(1+4N e m)

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20 Isolation By Distance

21 PopulationsBCDE A0.02560.04530.02200.0465 B0.05620.01100.0375 C0.05040.0321 D0.0634

22 PopulationsBCDE A9.515.2811.115.13 B4.2022.486.42 C4.717.54 D3.69

23 PopulationsBCDE A0.02560.04530.02200.0465 B0.05620.01100.0375 C0.05040.0321 D0.0634

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25  AMOVA-Laurent Excoffier ARLEQUIN  http://cmpg.unibe.ch/software/arlequin3/ http://cmpg.unibe.ch/software/arlequin3/  Designed for mtDNAs initially  Takes various levels-populations and subpopulations, etc. molecular variation between them as a proportion of total molecular variance

26 Methods-Nested Clade Analysis (1) Templeton, A. (2006) Population genetics and microevolutionary theory. Wiley

27  D c : Clade distance: Geographical separation of individuals within a clade  D n : Nested clade distance: Distance from the centre of a clade and the mean location of individuals in related clades (all those within the same higher level of nesting)  Isolation by distance: A clade-defining mutation arises in a single location, and its spread will increase with age. Clades within that clade (nested clades) will have a geographic distribution within that of the ancestral clade.  Fragmentation: Strict correlation of clades with geography- which breaks down as older clades are considered.  Range Expansion: Subclades can be more widespread geographically than their ancestral clades.

28  Samples individuals and genotypes at many loci  Creates subpopulations where there are Hardy-Weinberg proportions and linkage equilibrium within subpopulations  Assigns individuals to subpopulations  http://pritch.bsd.uchicago.edu/structure.html http://pritch.bsd.uchicago.edu/structure.html Methods: STRUCTURE - Jonathan Pritchard

29  G. Guillot, Estoup, A., Mortier, F. Cosson, J.F. A spatial statistical model for landscape genetics. Genetics, 170, 1261-1280, 2005.  http://www2.imm.dtu.d k/~gigu/Geneland/ http://www2.imm.dtu.d k/~gigu/Geneland/ Methods-GENELAND

30  Selective Sweeps  Complete or partial  Locus-specific

31 Natural Selection  Effects on F ST ◦ Balanced polymorphism throughout species range gives low F ST ◦ Geographically localised selection gives high F ST


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