Fitness and distribution of cell types.

<p>Parameters: <i>n</i> = 20, <i>μ</i> = 10⁻⁴, <i>c</i>_<i>h</i> = 0.2 and concave fitness. <i>U</i>₁<i>B</i>₂ cells appear at generation 0, which is the point at which the <i>B</i>₁ and <i>B</i>₂ gametes reach mutation-selection equilibrium. <b>(A)</b> Relative advantage of each genotype through time (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005112#sec013" target="_blank">Model for details</a>). For <b>B-E</b>, the relative proportion is the sum of a particular cell type divided by the sum of all cells that carry the same genotype. The heteroplasmic category includes all cells with any level of heteroplasmy. <b>B-C</b> shows the distribution of cells carrying the <i>U</i>₁<i>B</i>₂ genotype <b>(B)</b> and the <i>B</i>₁<i>B</i>₂ genotype <b>(C). D-E</b> show a more detailed distribution of cell types carrying the <i>B</i>₁<i>B</i>₂ genotype at generation 1350 <b>(D)</b> and at generation 1820 <b>(E)</b>. The decrease in heteroplasmy in <i>B</i>₁<i>B</i>₂ cells between generations 0–100 is an artifact of introducing <i>U</i>₁ at a frequency of 0.01 (the influx of <i>U</i>₁ gametes homoplasmic for the wild type haplotype converts some heteroplasmic <i>B</i>₁ and <i>B</i>₂ gametes into homoplasmic gametes, which increases the proportion of homoplasmic <i>B</i>₁<i>B</i>₂ cells). From generations 1350–1820, the proportion of heteroplasmic <i>B</i>₁<i>B</i>₂ cells decreases <b>(C)</b> but the level of heteroplasmy increases (compare <b>D</b> with <b>E</b>). This more than offsets the decrease in the proportion of heteroplasmic cells and <math><mrow><msub><mrow><mi>w</mi><mo stretchy="true">¯</mo></mrow><mrow><msub><mi>B</mi><mn>1</mn></msub><msub><mi>B</mi><mn>2</mn></msub></mrow></msub></mrow></math> continues to decrease <b>(A)</b>.