Which phrase describes a gene in its simplest form?

a. a looped portion of RNA

b. a part of a protein

c. a molecule found in the endoplasmic reticulum

d. a segment of DNA

Option-D, a segment of DNA

Explanation:

A gene represents the particular segment of DNA which contains the instruction for the trait of an organism. The nucleotide sequence present in the segment provides the instruction in the form of codons.

The gene is present in the form of its alternative form called alleles which are located on the chromosomes at locus. The alleles represent the variants of the gene and therefore controls the two variety of a single trait.

Thus, Option-D is correct.