Final answer:
Chromosomes are the threadlike structures within the nucleus that contain genetic material (DNA) and proteins. They are particularly visible and organized during cell division. In humans, each cell typically has 46 chromosomes that carry genetic information.
Step-by-step explanation:
The threadlike structures in the nucleus that contain genetic material (DNA) are known as chromosomes. These structures are composed of DNA and proteins and serve as the repositories for genetic information. Chromosomes are visible under a microscope especially when cells are undergoing division.
During interphase, the less condensed form of chromosomes is called chromatin, where DNA is wrapped around histone proteins. However, when a cell is preparing to divide, the chromatin condenses into the more recognizable and tightly packed chromosomes, to ensure the safe distribution of DNA to daughter cells. Human cells, for example, contain 46 chromosomes, which house almost 22,000 genes.