Infectious agents are those that corrupt and prey on an organism or a host. This is sometimes called parasitism when a foreign organism consumes a host by preying on its nutrients and food. Hence, we are uncertain in Anna's case because there is no clear description of her symptoms.
It is important that it has half because there is a half that comes from each parent. so to equal it all out human gametes have a half set of dna instead of a full set
