title: Color one point and add an annotation in ggplot2?
body: <p>I have a dataframe <code>a</code> with three columns :</p>
  
  <p><code>GeneName</code>, <code>Index1</code>, <code>Index2</code></p>
  
  <p>I draw a scatterplot like this</p>
  
  <pre><code>ggplot(a, aes(log10(Index1+1), Index2)) +geom_point(alpha=1/5)
  </code></pre>
  
  <p>Then I want to color a point whose <code>GeneName</code> is <code>"G1"</code> and add a text box near that point, what might be the easiest way to do it?</p>