The meaning of genetic novelty

[noha]

Hello,

I am translating a book called Microbiology: A very Short introduction, and I don't understand the meaning of arbitrary measures of genetic novelty in the following context:

The application of the term ‘species’ is even more problematic for viruses than bacteria and we rely upon arbitrary measures of genetic novelty when we refer to different kinds of bacteriophage.

[Sensei]

Quote

The meaning of genetic novelty

Random mutation. First seen just because it has just appeared in your lifetime. e.g. resistance to drugs that have just been made by human.

[noha]

what do you mean by random mutation here?

[swansont]

Novelty would mean something that is different, so they are looking at unique genetics of one virus vs another. The "arbitrary measure" suggests that some genetic differences might not matter in distinguishing between them, i.e. some measure of genetic difference might tell you that two viruses are different, when they should be classified as being the same virus. (or vice-versa)

[bangstrom]

I would interpret “arbitrary measures” to mean that there is no established protocol for naming bacteriophages especially when it comes to the selection of letters. Generally, the first person to characterize a new virus picks an arbitrary letter from the Greek or Roman alphabet followed by the number 1 followed by the genus of the bacteria they infect. Other variants are given numbers in sequence of their discovery. There is no systematic meaning to the choice of letters.

[swansont]

1 hour ago, bangstrom said:

I would interpret “arbitrary measures” to mean that there is no established protocol for naming bacteriophages especially when it comes to the selection of letters. Generally, the first person to characterize a new virus picks an arbitrary letter from the Greek or Roman alphabet followed by the number 1 followed by the genus of the bacteria they infect. Other variants are given numbers in sequence of their discovery. There is no systematic meaning to the choice of letters.

The label is beside the point. 

[bangstrom]

3 hours ago, swansont said:

The label is beside the point. 

What does that mean? Bacteriophages are not given genus and species names they are identified by numbers and letters.

[CharonY]

OP was asking about arbitrary measures in order to categorize phages (i.e. ways to measure genetic distance), and was not referring to naming conventions as such. 

IOW it is not about how systematic we name phages, but rather how systematic (or not) are we able to distinguish them in the first place.