The in-game hint:
To clarify a bit:The Virocyte is a cell infected with a virus. If another cell touches this cell it risks also getting infected unless it is protected by a Keratinocyte. Part of this cells genome will get copied into the other cell when it gets infected. This is very much how a virus works in nature.
Which part of the genome gets copied is specified by the "Virus copy from" property in the genome editor. Where it is copied into the victim cell is specified by the "Virus copy to" property. Note that not only the genes for one mode are copied but also the genes for the modes of 2 generations of descendants. So a maximum of 1+2+4 modes of the host genome are copied to the newly infected cell.
In this challenge you are supposed to kill all the initial cells by infecting them with a virus.
A Virocyte represents not actually a virus particle, but a cell infected with and spreading a virus. It is thus still a cell and it still has 15 modes in its genome.
The virus itself is just a piece of DNA that incorporates itself into the victims of infection. This "piece of DNA" exist in the Virocyte and the property "Virus copy from" specifies what part of its DNA that make up the transferred virus particle.
Let's say we have a cell A, where mode 3 is of type Virocyte, mode 10 is of type Flagellocyte, and that cell A is currently in mode 3.
A's mode 5 has property "virus copy from" set to 10.
Let's say we have a cell B, where mode 4 is of type Photocyte and that cell B is currently in mode 4.
Now A and B touch. This means that a virus particle containing DNA from mode 10 of cell A will be transferred into cell B. Where will this DNA end up? That is dictated by cell A's mode 3's setting, "virus copy to". If this is mode 4, then we will immediately see cell B become a Flagellocyte and swim away. If "virus copy to" is set to, say 5, then mode 5 will be overwritten by everything in cell A's mode 10. But since cell B is in mode 4, and not 5, we will not immediately see a difference after it was infected, unless we investigate it's genome.
More modes are sometimes copied as well since two generations of descendants are copied as well. This means that whatever modes mode 10 of A would have split into will also be copied and their daughter modes as well. All relative positions are conserved so if mode 10 splits to 9 and 7, they would always be pasted into where mode 10 is pasted, -1 and -3 respectively.
Descendants example: Virocyte copies from mode 5 to mode 8.
Mode 5 of Virocyte splits to 4 and 3, which respectively split to 2,2 and 3,3.
Then these copies will be done:
5 → 8
4 → 7
3 → 6
2 → 5
Hope this clears up a bit! Viruses are complicated and modifications of the genome can have unintended consequences, don't expect to get it right the first time! These challenges are left as the last one of a reason