What are the basic units of heredity?

Genes are recognized as the fundamental units of heredity. They are segments of DNA that contain the instructions for building and maintaining the organisms’ characteristics and functions. Genes dictate traits such as eye color, flower color, and susceptibility to diseases, among many others, and are passed from parents to offspring during reproduction.

While chromosomes are structures that house genes, they are not the basic units themselves; instead, they are the carriers of many genes. Alleles represent different versions of a gene that can vary in expression—for example, one allele may result in brown eyes while another leads to blue eyes. Nucleotides, on the other hand, are the building blocks of DNA and RNA, forming the genetic code, yet they do not represent heredity units on their own. Thus, the specific and critical role of genes in inheritance and trait determination highlights why they are considered the basic units of heredity.