There are two DNA popups that appear – the yellow ones and the red ones. They will pop up for multiple reasons. The yellow ones will pop up randomly over a country that has already been infected, regardless of how many people in that country are actually infected. Red ones will always pop up over a newly infected country, and are gone after that. Both of these will earn you one DNA per tap.
Want to make more of the free gem popups appear? Look for them whenever you buy large loads of transmissions, because they will pop up in place of red DNA bubbles when new countries are infected, especially when infections are spreading extremely rapidly. This is another reason why it’s good to load up on transmissions all at once rather than one by one.
Sometimes you’ll play and it will simply become obvious to you that the current attempt is going down the tubes. Whenever that happens, go to the menu screen in the middle of the game and hit restart. The menu button is the one in the upper left hand corner of the screen.
Gene mutations will occur randomly sometimes, but they tend to occur when high infection rates are happening (not high death rates). To increase the probability of them happening, as stated previously, buy loads of transmissions all at once rather than one at a time. The faster people are getting infected, the more frequently you will see them.
There are some strange continuity errors that happen in this game. For example, if you get bored (especially in Frenzy mode) and you haven’t purchased anything yet, wait something like 150-200 years, and the first person who got infected by the pathogen will still be alive. Without the disease, people in this game live forever yet they never breed.
It’s possible to infect everyone without buying any airplane-related transmissions. However, you will never be able to infect everyone without buying any of the ship-related transmissions, because ships are the only way to get to certain small island countries, such as Madagascar or Greenland. Cross-border transmissions, though, make airplane transmission useless.