Question: We all know how an electric current causes magnetic fields. But when a single electron is flowing through the wire, how is this electron creating the magnetic field or how are electrons responsible for magnetic field around a wire?

Answer: 
The ratio of dark to baryonic matter is 5.25 in the first diagram and 5 in the second diagram, but I don't think the difference is significant. We don't know the densities with absolute certainty, especially near the Big Bang, and the small difference between the ratios is probably just down to the uncertainties in the densities.

We would expect the ratio to stay fixed because the densities both scale as $a^{-3}$, where $a$ is the [scale factor](http://en.wikipedia.org/wiki/Scale_factor_(cosmology)). For comparison the density of relativistic matter (photons and neutrinos) scales as $a^{-4}$ and density of dark energy stays constant i.e. it doesn't depend on $a$ at all. That's why the photons and neutrinos have disappeared in the second diagram while a large chunk of dark energy has appeared.

As far as I know there is no mechanism for dark and baryonic matter to interconvert, or for either to disappear.
I the very early universe there was very little atoms. Atoms are mainly made from exploding stars. I the first pie chart there are less atoms and more photons. This is because that was the initial state and the universe. It was highly fence with photons and neutrinos going in all directions.
They will be more of all materials in the second pie chart. For matter and universe has increased in volume with starts ending and expelling larger atoms. The Higgs field continues to create matter. Its just the ratios that have changed. Its not worth put the photons and neutrinos on the second pie chart. Although there quantity has dramatically increased the ratios now are so much lower that the atom ratio.
More humility learning needs to come before your question about dark matter ratios can be answered.