Question: when was the location of genetic information on chromosomes established

title: Gene
text: Essential genes are the set of genes thought to be critical for an organism 's survival . This definition assumes the abundant availability of all relevant nutrients and the absence of environmental stress . Only a small portion of an organism 's genes are essential . In bacteria , an estimated 250 -- 400 genes are essential for Escherichia coli and Bacillus subtilis , which is less than 10 % of their genes . Half of these genes are orthologs in both organisms and are largely involved in protein synthesis . In the budding yeast Saccharomyces cerevisiae the number of essential genes is slightly higher , at 1000 genes ( ~ 20 % of their genes ) . Although the number is more difficult to measure in higher eukaryotes , mice and humans are estimated to have around 2000 essential genes ( ~ 10 % of their genes ) . The synthetic organism , Syn 3 , has a minimal genome of 473 essential genes and quasi-essential genes ( necessary for fast growth ) , although 149 have unknown function .