It is associated with more or less why a genetic counselor would need to look at distinct human populations, with which an individual is related to when doing certain kinds of tests. For instance, if someone knows about their ancestry then the counselor would be able to tell about the genetic disorders most commonly occurring in that particular ancestry.
The basic way of seeing at it from a population genetics point of view is how populations do differ genetically and how does it associate with the probabilities of exhibiting a mutation in the person.
Infectious diseases are caused by the passing of one person to another. Corona is an example. Noninfectious diseases, they are just spread by pathogens. Good luck!
