morphological variation in Panaxia dominula

1
morphological variation in Panaxia dominula
P. d. dominula cdcd
P. d. medionigra cdcb
P. d. bimacula cbcb
2
PO7 275kb
Microsatellite loci for Pogonomyrmex
occidentalis
PO8 250kb
PO3 160kb
PO1 175kb
3
Quantifying population genetic variation
genotype frequency
particular genotype total number of
individuals
particular allele total number of alleles
allele frequency
by the law of proportions, both genotype and
allele frequencies always sum to one
4
genotype A1A1 A1A2 A2A2 number 670
200 130
genotype 670 200 130 frequency 1000
1000 1000
geno freq. 0.67 0.20 0.13
1 2
frequency of A1 0.67 (0.20) 0.77
12
frequency of A2 0.13 (0.20) 0.23
5
Hardy-Weinberg Equilibrium
In the presence of certain conditions, the
genotype frequencies of a population will be
stable over time, and will be directly
predictable from the allele frequencies. If the
population is not at equilibrium, it will achieve
it after one generation of random
mating. Assumes no mutation, no selection,
infinite population size, no gene flow, random
mating
Null model for describing population
genetic variation
6
Type of Mating Freq. Offspring genotype
frequencies male x female A1A1 A1A2 A2A2 A1
A1 x A1A1 P2 P2 A1A1 x A1A2
PH ½ PH ½ PH A1A2 x A1A1 PH ½ PH ½
PH A1A1 x A2A2 PQ PQ A2A2 x A1A1
PQ PQ A1A2 x A1A2 H2 ¼ H2 ½ H2 ¼
H2 A1A2 x A2A2 HQ ½ HQ ½ HQ A2A2 x
A1A2 HQ ½ HQ ½ HQ A2A2 x A2A2
Q2 Q2 Total (P H Q)2 (P
½H)2 2(P ½H)(Q ½H) (Q ½H)2
1 p2 2pq q2
7
generally if alleles Ai Aj Ak
with frequencies p f(Ai) q f(Aj)
r f(Ak) then f(Ai Ai) p2
f(Ai Aj)2pq f(Ai Ak) 2pr and
f(Ai Ai ) f(Ai Ai) f(Ai Ak) f(Ai
Ak) and f(Ai ) f(Ai) f(Ak)
f(Ak)
8
testing whether a population is in HWE
genotype MM MN NN number 60 20
20 obs. gen. fr. 0.6 0.2 0.2 f(M)
0.6 0.1 0.7 f(N) 0.2 0.1 0.3 exp.
gen. fr. f(M)2 2f(M)f(N) f(N)2
(0.7)2 2(0.7)(0.3) (0.3)2
0.49 0.42 0.09
9
Compare observed and expected genotype
distributions with a goodness of fit chi-square
test with n-2 degrees of freedom c dof
S
(obs. gen. fr. - exp. gen. fr.)2
(exp. gen. freq.)
for the data on the previous page c 1
727.0 p lt 0.001
10
HWE is not a good null hypothesis for
empiricists -- property of zygotes, not
adults -- not very sensitive to many of the
conditions -- not very sensitive unless
large sample size -- single snapshot of
population variation A1A1 A1A2
A2A2 gen 1 0.36 0.48
0.16 gen 2 0.56 0.38 0.06
11
HWE and sex-linked genes
autosomes half of the alleles in each sex sex
chromosomes two-thirds of the alleles in
the homogametic (XX) sex
if males are homogametic, A1A1 A1A2
A2A2 A1/ A2/
males females
allele frequencies are sex-specific pm, qm and
pf, qf
12
Under random mating qm (qm qf)
males get an X-chromosome from each
parent qf qm females get their only
X-chromosome from their father if qm
qf, oscillatory approach to equilibrium
1 2
gt
gt
1 3
1 3
2 3
2 3
p pm pf q qm qf
13

14
genetic diversity characterizes most natural
populations Hardy-Weinberg Equilibrium
represents a null model for the evolution of
genotype frequencies basis for mathematically
examining the effects of mutation, selection,
genetic drift, gene flow, and non-random
mating dynamics of HWE differ for sex-linked
genes
15

• Homework below are data from two sites on the
  frequency of genotypes at
• the esterase locus in cotton rats. There are two
  codominant alleles, fast (f)
• and slow (s), and three genotypes. Annual
  samples are collected and given
• below.
• Galveston Island S.P. UH Coastal Center
• f/f f/s s/s n f/f f/s s/s n
• 0.25 0.50 0.25 80 0.36 0.48 0.16 40
• 0.445 0.445 0.110 77 0.563 0.375 0.063 41
• 0.639 0.320 0.041 82 0.734 0.244 0.021 36
• Do any samples deviate significantly from HWE?
  On the basis of these
• results, what can you conclude?