Simplify the following text for a Grade 12 native English-speaking person.
Original: He identified that chromatin was correlated to threadlike structures in the cell nucleusâ '' the chromosomes ( meaning colored body ) , which were thus named later on by German anamist Wilhelm von Waldeyer-Hartz ( 1836 â `` 1921 ) .
Simplified: He identified that chromatin was correlated to threadlike structures in the cell nucleus -- the chromosomes ( meaning colored body ) .