Describe the composition, structure, and types of chromosomes.

(N/A) $ \Rightarrow $ Chromatin contains $DNA$, some basic proteins called histones, some non-histone proteins, and also $RNA$. $A$ single human cell has approximately $2 \, m$ long thread of $DNA$ distributed among its $46$ chromosomes ($23$ pairs).
$ \Rightarrow $ Every chromosome essentially has a primary constriction or the centromere, on the sides of which disc-shaped structures called kinetochores are present.
$ \Rightarrow $ Based on the position of the centromere, chromosomes are classified into four types:
$ \Rightarrow $ Metacentric: The metacentric chromosome has a middle centromere forming two equal arms of the chromosome.
$ \Rightarrow $ Sub-metacentric: The sub-metacentric chromosome has a centromere slightly away from the middle of the chromosome, resulting in one shorter arm and one longer arm.
$ \Rightarrow $ Acrocentric: In the case of an acrocentric chromosome, the centromere is situated close to its end, forming one extremely short and one very long arm.
$ \Rightarrow $ Telocentric: $A$ telocentric chromosome has a terminal centromere.