What are threadlike structures made of DNA that contain genes?

The correct response identifies chromosomes as the threadlike structures composed of DNA that house genes. Chromosomes are essential components of the cell nucleus, and they ensure the proper distribution of genetic material during cell division.

Each chromosome is made up of DNA tightly coiled around proteins called histones, which help organize and protect the DNA strands. These structures are crucial for the replication and segregation of genetic material, providing instructions for the development, functioning, growth, and reproduction of all living organisms. The DNA within the chromosomes includes various segments called genes, which dictate specific traits or functions in an organism.

In contrast, ribosomes are not comprised of DNA but rather are molecular machines that synthesize proteins based on the instructions provided by mRNA. Centromeres are the regions on chromosomes that are essential for the proper alignment and separation of sister chromatids during cell division, but they are not the entire structure comprising genes. Chromatids refer to the duplicated arms of a chromosome that are joined at the centromere prior to cell division. Therefore, chromosomes are the correct answer as they directly relate to the DNA structures that encompass genes.