<span>First determining if the cells in the tumor have common and the unique genetic and biochemical marker and if they are present, that would clearly mean that they all were created from a initially mutated cell and formed the marker and these are considered as monoclonal. If that is not the case and cells do not have a common origin, these are called as polyclonal.</span>
In population genetics, directional selection also know as positive selection is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype
<span>It shows the "rank" of the organism. Cladistics show the probable sequences of origins as well as shared and derived characteristics but no ranks.</span>
A prokaryotic cell might be recognized by the presence of flagellates used to move (the four long filaments located posterior to the cell). There are also many pili surrounding the cell wall (the small little filaments). There are almost no organelles. There is a circular DNI molecule concentrated in a nucleoid (which seems to be the grey oval in the middle of the cell). Prokaryotic cells also have different compartments that depend on the type of cells, such as chlorosome, carboxysome, phycobilisome, and others (which might be the dark spiral circle in the anterior part of the cell).
Two differences with the cell of an onion peel are that the onion peel cell has its genetic material surrounded and protected by the nucleus membrane, whereas the prokaryotic cell lacks a delimitated nucleus. Also, the onion peel cell has a hexagonal shape and lacks flagellates and pili, unlike the prokaryotic cell, which uses the to move. The onion peel is a multicellular structure, while the prokaryote is a one-celled organism.
There should always be a cover glass over the cell or tissue we are looking at. Fasten the slide with the stage clips. Move the lens carefully in order not to damage it or the slide. Do not touch or clean the lens with the fingers and try not to stain them.
