What are the threadlike structures made of DNA that contain genes known as?

The threadlike structures made of DNA that contain genes are known as chromosomes. Each chromosome consists of a long strand of DNA that is coiled and condensed, allowing it to fit within the nucleus of a cell. Chromosomes carry the genetic information necessary for the growth, development, and functioning of an organism.

Chromosomes are crucial during cell division, as they ensure the accurate replication and distribution of genetic material. Each species has a specific number of chromosomes; for example, humans typically have 46 chromosomes organized into 23 pairs.

In contrast, chromatids refer to one-half of a duplicated chromosome and are connected by a centromere until they are separated during cell division. Centromeres are the regions where chromatids are attached, and nucleotides are the basic building blocks of DNA, not structures themselves. Therefore, chromosomes are the correct answer as the primary carriers of genetic information in the form of genes.