Final answer:
A segment of DNA that encodes a specific protein is called a gene, which is organized on chromosomes. Most genes code for a single protein, and are pivotal in the transfer and expression of hereditary information.
Step-by-step explanation:
A portion of DNA that encodes a specific protein is called a gene. Genes are the physical and functional units of heredity, consisting of a sequence of DNA that codes for a specific peptide or RNA molecule. The genetic code within these genes operates through a series of three-letter codes known as codons, each of which specifies a particular amino acid.
Chromosomes are larger structures within the cell's nucleus, made up of coiled DNA and proteins, containing hundreds or thousands of genes. The DNA in chromosomes carries the genetic instructions for making proteins, and chromosomes are divided into functional units known as genes, with most genes containing the instructions for a single protein.
During cell division, chromosomes replicate, forming X-shaped structures made up of two identical halves called chromatids, joined at a region known as the centromere. The centromere is associated with proteins called kinetochores to which spindle fibers attach during mitosis.