Lymph node
disruptive selection
Homozygotes for one allele are favored over all others.
natural selection
Are those individuals best adapted to their immediate environment.
If it is easier or more likely that an organsim is going to survive and reproduce if that organism works together with another or takes advantage of a certain opportunity, natural selection will favor the organisms that are more suited to maintaining their realtionship with the other organism.
spleen
Disruptive Selection
natural selection
natural selection
antigen. Helper B and T cells most likely.
Dolphins.
An antigen isn't supposed to be in your body. That is what an antigen means. So, although there are likely many (bacteria, viruses, pollen, etc.), there is no set number.
Anyone can challenge anyone! But likely than not the right person will prevail.
The likely word is "challenge" (a test, contest, or duel).
Answer Class II MHC protein. Class II are found in membranes of antigen-presenting cells-phagocytic cells and lymphocytes. The liver performs phagocytosis and antigen presentation.
natural selection
Most likely on the rooftops.