This is an outstanding photograph of Annas hummingbird' The species usually

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This is an outstanding photograph of Annas
hummingbird. The species usually lives in
California, but this was taken in Texas, well
outside the normal range of the species. No one
knows why western species are now moving east
after the native species, the rubythroat, has
mostly gone south.
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Equations to know and love
Popln. Size/genetic drift
Ht H0(1-1/2Ne)t
Migration/gene flow
Mutation
Equil./overdominance
Ne 4NmNf / (Nm Nf) 1/Ne 1/t ? 1/Nt
or 1/tt 1/Nt1 1/Nt2 1/Nt3.
pi(1) (1-m)pi(0) mpc or m (pi(1) -
pi(0))/ (pc - pi(0)) ?pi m(pc - pi)
Pn p0e-un
qeq s1/(s1 s2)
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Lect. 9 1. Molecular markers, their
interpretation and uses. 2.
Assumptions of HW, derivation of HW and its
significance
Lect 10 1. Establishing HW equil.
2. HW equil for gt2 alleles 3.
Approach to equil multiple genes and for
X-linked genes BE SURE TO SEE THE PROBLEMS
WORKED OUT IN THIS LECT.
Lect 11 1. Effects of finite popln size, genetic
drift. 2. Loss of
heterozygosity, 3. Popln bottlenecks,
founder effect
Lect 12 1. Effective popln. size 2.
Inbreeding and inbreeding depression (incl
exceptions) 3. Assortative
mating ( and -)
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Lect 13 1. Migration and gene flow.
2. Models of population structure (island
etc.) 3. Homogenizing effects of
gene flow 4. Models of mutation
5. Significance of mutation
6. Mutation and change of gene
frequency
Lect 14 1. Most likely fate of new mutations
2. Concept of fitness.
3. Hard vs soft selection 4.
Phenotypic modes of selection (directional,
stabilizing, etc.) 5. Selection
coefficients 6. Calculation of
change in gene frequencies under selection.
7. Calculation of average fitness
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Lect 15 1. Relationship of ?q to q.
2. Overdominance and equil. gene freqs.
3. Sickle cell anemia and malaria
Lect 16 1. Frequency-dependent selection and its
signfiicance. 2. Evol. Arms race
and other models. 3. Batesian,
Mullerian, Disguise and Aggressive mimicry
aposematic coloration.
Lect 17 1. More on mimicry. 2.
Sex and recombination. 3.
Mullers ratchet (mutational decay)
4. Sex and linkage disequilibrium
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There are cases of mimicry that are not easily
explained.Here is one that I happened upon in
Mexico in 1980 while doing fieldwork around Lake
Chapala The fish in the left column are young
of the predator, Alloophorus robustus those in
the right column are the young of its common
prey, Goodea atripinnis. The adults of these
species can be easily told apart. But the young
can hardly be told apart except on very close
examination even though the adults of each
species have distinctive markings. A resemblance
this close is almost certainly not
coincidental, but no one knows its biological
significance. These species are part of a
unique fish fauna on the central Mexican
plateau, the Goodeidae. That fauna, once
abundant, is now largely highly threatened and
several species are already gone. Consequently,
we may never understand the basis of this
unusual mimicry of predator and prey.
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SEX RECOMBINATION
Recombination 1. Independent assortment of
alleles of 2 or
more genes on different csomes e.g. AABB x aabb
-gt F1 AaBb -gt meiosis -gt Parental
gametes AB ab
and Nonparental gametes
Ab
aB 2. Crossing over between genes on the same
csome A B aB a b
Ab Nonparental gametes
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AmBmCfDm
AmBfCfDm
AmBfCfDf
AfBfCfDf
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Significance and implications of sex
Mullers ratchet in asexual populations
AfBfCfDf AmBfCfDf
AmBfCfDm AmBmCfDm
AfBfCfDm AfBmCfDf AfBfCmDf
AfBfCmDm
AfBmCfDm AmBfCmDf
AfBmCmDm AmBmCfDm
AmBfCmDm
one mutation
two mutations
three mutations
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Significance and implications of sex
Mullers ratchet in asexual
populations AmBfCfDf AmBfCfDm
AmBmCfDm AfBfCfDm
AfBmCfDf AfBfCmDf
AfBfCmDm AfBmCfDm
AmBfCmDf
AfBmCmDm AmBmCfDm
AmBfCmDm
Eventually, the mutation-free genotype, AfBfCfDf,
becomes so rare that it disappears by drift.
Now, the most fit genotypes in the population
have one mutation---there is no way of getting
back to the AfBfCfDf genotype--the ratchet is
said to have clicked once.
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AmBfCfDm AmBmCfDm
AfBfCmDm AfBmCfDm
AmBfCmDf
AfBmCmDm AmBmCfDm
AmBfCmDm
The process repeats, and the one-mutation
genotypes eventually disappear and the ratchet
clicks again. And, eventually, again and
again...
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• Linkage Disequilibrium
• Remember that when considering two genes,
• A and B, each gene will reach HW equil.
  within
• a single generation of random mating. BUT
• When considered together A and B will not
• immediately be in equilibrium with
  eachother

To see this more clearly, define p,q as f(A,a)
and r,s as f(B,b) At joint equilibrium f(AB)
pr, f(Ab) ps, f(aB) qr and f(ab) qs
But suppose we started with
linked genes like this A B and a b
(no Ab or aB), then f(AB) gtgtpr, etc In order
to get to equilibrium we have to have
recombination And if the genes are closely
linked, it may take many generations.
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RECOMBINATION DESTROYS LINKAGE DISEQUILIBRIUM
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Models Batesian mimics
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No white patch
Orange patch
Black trailing edges
White patch
2nd white patch
Reddish trailing edges
And yet complex polymorphisms like those
involved in mimicry must be based on
combinations of specific alleles inherited
together.
What would be a likely fate for a butterfly that
looked like the upper one, but had a white patch
instead of an orange one, or reddish trailing
wing edges?
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No white patch
Orange patch
Black trailing edges
White patch
2nd white patch
Reddish trailing edges
In short, these polymorphisms must involve some
level of linkage disequilibrium. How is this
maintained in the face of sexual reproduction?
How do these butterflies have their cake and eat
it too?