Chromosomes are composed of complex molecules known as

DNA

Explanation:

Chromosomes are X-shaped structures in the cells of living organisms and the form genetic material is transferred to offsprings. Chromosomes are composed of long polynucleotide chains called DNA. Deoxyribonucleic acid or DNA is the stored form of genetic material in cells. They contain the information needed by an organism's for survival.

DNA is a very long chain of nucleotides, hence, in order to fit into a cell, the cell devises a means by wrapping the long DNA around certain proteins called HISTONES. The initial wrapping of DNA around the core of histone proteins form the NUCLEOSOME structure. The nucleosome is then further coiled around histones to form CHROMATIN. Chromatin later condenses during cell division to form the visible CHROMOSOME structure.

In a nutshell, a chromosome contains a complex long strands of DNA molecules, the genetic material.

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