The development of an organism — from a fertilized egg, through embryonic and juvenile stages, to adulthood — requires the coordinated expression of sets of genes at the proper times and in the proper places. Studies of several bizarre mutations in the fruitfly, Drosophila , provided keys to understanding the molecular basis of large-scale developmental plans. Early embryonic genes express proteins that set up the orientation and define the body segments of the fly embryo. Then "homeotic" genes act on the segments to make the body parts distinct to each segment.
Relays were invented in 1835 by American electromagnetism pioneer Joseph Henry ; in a demonstration at the College of New Jersey , Henry used a small electromagnet to switch a larger one on and off, and speculated that relays could be used to control electrical machines over very long distances. Henry applied this idea to another invention he was working on at the time, the electric telegraph (the forerunner of the telephone), which was successfully developed by William Cooke and Charles Wheatstone in England and (much more famously) by Samuel F. B. Morse in the United States. Relays were later used in telephone switching and early electronic computers and remained hugely popular until transistors came along in the late 1940s; according to Bancroft Gherardi, marking the 100th anniversary of Henry's work on electromagnetism, there were an estimated 70 million relays in operation in the United States alone by that time. Transistors are tiny electronic components that can do a similar job to relays, working as either amplifiers or switches. Although they switch faster, use far less electricity, take up a fraction of the space, and cost much less than relays, they generally work with only tiny currents so relays are still used in many applications. It was the development of transistors that spurred on the computer revolution from the mid-20th century onward. But without relays, there would have been no transistors, so relays—and pioneers like Joseph Henry—deserve some of the credit too!
Genes are maintained over an organism's evolution, however, genes can also be exchanged or "stolen" from other organisms. Bacteria can exchange plasmids carrying antibiotic resistance genes through conjugation, and viruses can insert their genes into host cells. Some mammalian genes have also been adopted by viruses and later passed onto other mammalian hosts. Regardless of how an organism gets and retains a gene, regions essential for the correct function of the protein are always conserved. Some mutations can accumulate in non-essential regions; these mutations are an overall history of the evolutionary life of a gene.