Final answer:
Chromosomes are the threadlike structures within cell nuclei that carry genetic information encoded in DNA, tightly coiled around histone proteins. They become highly visible during cell division and every species has a specific number of chromosomes that make up its genome.
Step-by-step explanation:
The threadlike structures that contain genes are called chromosomes. These are essential components found within the nucleus of cells. Chromosomes are made of DNA and proteins, and they carry a vector of genetic instructions necessary for the growth, development, and reproduction of organisms.
Each chromosome consists of DNA that is tightly coiled around proteins called histones, forming a structure known as chromatin. During cell division, chromatin condenses into visible chromosomes, ensuring DNA is correctly divided and distributed to daughter cells. Humans, for example, have 46 chromosomes containing about 22,000 genes that code for proteins, regulate cellular activities, and maintain the organism.
The entire genetic content of a cell, including all of its chromosomes, is known as the genome. The study of genomes is called genomics, encompassing eukaryotes, where the DNA and histones form the chromatin leading to the chromosome structure during cell division. Every eukaryotic species has a characteristic number of chromosomes that specifies its genetic blueprint.