Which of the following is a basic unit of heredity?

• A. Allele
• B. Gene
• C. Chromosome
• D. Nucleotide

Answer: (B)

Heredity operates through discrete units that carry instructions for traits. A gene is that defined DNA segment whose sequence provides the instructions to make a product that influences a trait. Because genes are inherited from parent to offspring and can come in different versions (alleles) that affect how traits are expressed, they serve as the basic unit of heredity. Nucleotides are the building blocks of DNA, not the units of inheritance themselves. Chromosomes are long DNA molecules that organize many genes, while alleles are variants of a gene. Therefore, the gene is the correct choice.