Fitness and distribution of gamete 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 gametes 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 gamete 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-F</b>, the relative proportion is the sum of a particular gamete type (e.g. a homoplasmic wild type <i>U</i>₁ gamete) divided by the sum of all cells carrying that allele (all gametes carrying the <i>U</i>₁ allele). Thus, the relative proportion describes how an allele is distributed across different gamete types but it does not show their actual frequencies in the population. The heteroplasmic category combines all gametes with any level of heteroplasmy. <b>B-D</b> show the distribution of gametes carrying the <i>U</i>₁ allele <b>(B)</b>, <i>B</i>₁ allele <b>(C)</b> and the <i>B</i>₂ allele <b>(D)</b>. <b>E-F</b> show a more detailed distribution of gametes carrying the <i>B</i>₁ allele at generation 1350 <b>(E)</b> and generation 1820 <b>(F)</b>. The decrease in heteroplasmy in <i>B</i>₁ and <i>B</i>₂ gametes 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). From generations 1350–1820, the proportion of heteroplasmic <i>B</i>₁ and <i>B</i>₂ gametes decreases <b>(C and D)</b> but the level of heteroplasmy increases (compare <b>E</b> with <b>F</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></mrow></msub></mrow></math> continues to decrease <b>(A)</b>. Around generation 1350, <i>B</i>₂ gametes homoplasmic for mutant mitochondria begin to appear, which causes <math><mrow><msub><mrow><mi>w</mi><mo stretchy="true">¯</mo></mrow><mrow><msub><mi>B</mi><mn>2</mn></msub></mrow></msub></mrow></math> to increase and eventually converge with <math><mrow><msub><mrow><mi>w</mi><mo stretchy="true">¯</mo></mrow><mrow><msub><mi>U</mi><mn>1</mn></msub></mrow></msub></mrow></math>.