Question

i dont really understand this part "within nucleus an even more deeply staining area is visible, the nucleolus, which is made of loops of DNA from several chromosomes. the number of nucleoli is variable,one to five being common in mammals" i cant understand the last part

Answer 1

@Abmon98 http://www.thefreedictionary.com/nucleoli

Answer 2

There can be more than one nucleolus inside a nucleus. It means that most mammals have between 1 and 5 nucleoli per cell. The nucleus is different - almost all cells have one and only one, a few types of highly specialised cells like red blood cells do not have a nucleus at all.