Which term refers to threadlike structures that contain genes?

The term that refers to threadlike structures containing genes is chromosomes. Chromosomes are organized structures of DNA and proteins found in the nucleus of eukaryotic cells. Each chromosome is composed of a single DNA molecule that is tightly coiled and packed with proteins, facilitating the efficient storage and transmission of genetic information during cell division.

Genes are segments of DNA located on these chromosomes, and they carry the instructions needed for the development, functioning, growth, and reproduction of all living organisms. During the process of cell division, chromosomes ensure that DNA is accurately replicated and distributed to daughter cells, maintaining genetic continuity across generations.

The other choices represent different kinds of cellular components. Nucleotides are the building blocks of DNA and RNA, ribosomes are the sites of protein synthesis, and endosomes are involved in the transport of materials within cells. While these components are essential for various cellular functions, they do not contain genes in the way that chromosomes do.