What are chromosomes primarily composed of?

The correct answer is that chromosomes are primarily composed of genes. Genes are segments of DNA that contain the instructions for building proteins and controlling the various functions of an organism. Each chromosome is made up of tightly coiled DNA wrapped around histone proteins, and within that DNA, genes are organized in a specific sequence. This genetic information is crucial for heredity and the development of an organism, making genes the fundamental units housed within chromosomes.

While proteins, RNA, and cell membranes play important roles in cellular function, they do not constitute the primary composition of chromosomes. Chromosomes are primarily structures that organize and package the DNA, which includes the genes essential for genetic information and expression.