<P> Early work in molecular genetics suggested the concept that one gene makes one protein . This concept (originally called the one gene - one enzyme hypothesis) emerged from an influential 1941 paper by George Beadle and Edward Tatum on experiments with mutants of the fungus Neurospora crassa . Norman Horowitz, an early colleague on the Neurospora research, reminisced in 2004 that "these experiments founded the science of what Beadle and Tatum called biochemical genetics . In actuality they proved to be the opening gun in what became molecular genetics and all the developments that have followed from that ." The one gene - one protein concept has been refined since the discovery of genes that can encode multiple proteins by alternative splicing and coding sequences split in short section across the genome whose mRNAs are concatenated by trans - splicing . </P> <P> A broad operational definition is sometimes used to encompass the complexity of these diverse phenomena, where a gene is defined as a union of genomic sequences encoding a coherent set of potentially overlapping functional products . This definition categorizes genes by their functional products (proteins or RNA) rather than their specific DNA loci, with regulatory elements classified as gene - associated regions . </P> <P> In all organisms, two steps are required to read the information encoded in a gene's DNA and produce the protein it specifies . First, the gene's DNA is transcribed to messenger RNA (mRNA). Second, that mRNA is translated to protein . RNA - coding genes must still go through the first step, but are not translated into protein . The process of producing a biologically functional molecule of either RNA or protein is called gene expression, and the resulting molecule is called a gene product . </P> <P> The nucleotide sequence of a gene's DNA specifies the amino acid sequence of a protein through the genetic code . Sets of three nucleotides, known as codons, each correspond to a specific amino acid . The principle that three sequential bases of DNA code for each amino acid was demonstrated in 1961 using frameshift mutations in the rIIB gene of bacteriophage T4 (see Crick, Brenner et al. experiment). </P>

What is meant by the term single gene trait