Answer: The correct answer for the filling the blank is Gene.
Gene is a segment of DNA present in the genome of an organism. It carries information for the specific characteristics of the organism. It is also known as heredity unit as the information is carried from one generation to the next.
Two processes take place for gene expression. These are Transcription and Translation.
In transcription, DNA of the gene is converted to mRNA ( messenger RNA). A gene has a transcription start site from where transcription begins and a transcription stop site, which terminates transcription. mRNA contains start codon and stop codon for the initiation and termination of translation.
The translation of mRNA gives specific protein. Since the sequence of genes are very specific, therefore, one type of protein is coded by one gene.