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added prob_of_pL_2s
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cooplab committed Nov 25, 2015
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4 changes: 4 additions & 0 deletions chapter-05.tex
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Expand Up @@ -687,6 +687,10 @@ \subsection{Migration--selection balance}
migration-selection balance (at least under strong selection) is
analogous to mutation selection balance.\\

We can use this same model by analogy for the case of
migration-selection balance in a diploid model, in that case we replace
our haploid $s$ by the cost to heterozygotes $hs$.

\begin{tcolorbox}
\begin{question}
You are investigating a small river population of sticklebacks, which receives infrequent migrants from a very large marine population. At a set of (putatively) neutral biallelic markers the freshwater population has frequencies:
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18 changes: 14 additions & 4 deletions chapter-06.tex
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Expand Up @@ -24,6 +24,7 @@ \subsection{Stochastic loss of strongly selected alleles}
P_i= \frac{(1+s)^i e^{-(1+s)}}{i!}
\end{equation}


Consider starting from a single individual with the selected allele, and ask
about the probability of eventual loss of our selected allele starting
from this single copy ($p_L$). To derive this we'll make use of a
Expand All @@ -33,16 +34,18 @@ \subsection{Stochastic loss of strongly selected alleles}
\begin{enumerate}
\item In our first generation
with probability $P_0$ our individual leaves no copies of itself to
the next generation, in which case our allele is lost.
the next generation, in which case our allele is lost (Figure \ref{fig:Proof_of_pL_2s}A).
\item Alternatively
it could leave one copy of itself to the next generation (with
probability $P_1$), in which
case with probability $p_L$ this copy eventually goes extinct.
case with probability $p_L$ this copy eventually goes extinct (Figure \ref{fig:Proof_of_pL_2s}B).
\item It could leave two copies of itself to the next generation (with
probability $P_2$), in which
case with probability $p_L^2$ both of these copies eventually goes extinct.
case with probability $p_L^2$ both of these copies eventually goes
extinct (Figure \ref{fig:Proof_of_pL_2s}C).
\item More generally it could leave could leave $k$ copies ($k>0$) of itself to the next generation (with
probability $P_k$), in which case with probability $p_L^k$ all of these copies eventually go extinct.
probability $P_k$), in which case with probability $p_L^k$ all of
these copies eventually go extinct (e.g. Figure \ref{fig:Proof_of_pL_2s}D).
\end{enumerate}
summing over this probabilities we see that
\begin{eqnarray}
Expand Down Expand Up @@ -78,6 +81,13 @@ \subsection{Stochastic loss of strongly selected alleles}
probability of being lost when it is first introduced into the
population by mutation. \\

\begin{figure}
\begin{center}
\includegraphics[width=\textwidth]{figures/Proof_of_pL_2s}
\end{center}
\caption{} \label{fig:Proof_of_pL_2s}
\end{figure}

%%consider reparameterizing 1+(1-hs)s
We can also adapt this result to a diploid setting.
Assuming that heterozygotes for the $1$ allele have $1+(1-h)s$ children, the
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