The Search For and Descovery of The Gene

The Search For and Discovery of the Gene

     The recognition that inherited characteristics flow through generations of both plants and animals existed even in ancient times. A six thousand year old Babylonian tablet lists pedigrees of horses and possible inherited characteristics. Hippocrates, (460-375 BCE), postulated that each organ of the body grew from seeds that were passed from the father to the mother where they were reassembled. Aristotle (384-322 BCE), speculated that inherited characteristics were the result of purified blood shared during coitus, (we still talk of being related by blood). Man has been aware that some mechanism was behind the transfer of inherited characteristics long before he became civilized but had to wait for the advent of the scientific method of inquiry to uncover the chemistry involved. 

     The mechanisms of heredity began to be deciphered in the middle of the 19^th century when Gregor Mendel proposed that inherited characteristics were carried forward to the next generation in discrete units. Mendel used a strict methodology. He observed and recorded results. He then hypothesized and followed up with further experimentation and observation. His methods remain as the basis of genetic studies to this day.

     The evolution of living forms from disassociated groupings of single celled entities to multi-cellular forms is documented in nature’s hard cover books, (sedimentary rocks), and explained further in its soft cover books, (DNA). The examination of these records has given us an understanding of the developmental paths life has taken, and the ability to read the twisted threads that make up nature’s language of life. Nature describes life one individual at a time and in a series of sequential steps using only a four letter alphabet and simple grammatical rules. By allowing an occasional grammatical error and by demanding that variants comply with changing conditions, life persists. We call this thread language genetic information and each single fully formed description a Genome, each set of threaded sentences a Chromosome, and the discrete units described by Mendel, (sentences within chromosomes), we have named; Genes.

     The gene is the piece of the puzzle that Darwin lacked to fully explain the evolution of life by natural selection. Now we can see the gene, manipulate it, read its information, compare descriptions for various life forms and trace the history of living forms recorded in its descriptive codes. The gene is now out of the box along with a host of new questions that its appearance has prompted.

     As the concept of evolution coalesced, physical evidence for the idea was being accumulated. In 1869 a Swiss chemist, Johann Miescher, extracted a substance containing nitrogen and phosphorus from individual cell nuclei. We now know that what he extracted was the phosphate molecules that, along with sugar molecules, form the backbone of genetic strands and the nitrogen containing molecules that form part of the nucleotides of DNA. These nucleotides were later determined, in both plants and animals, to consist of four basic types; adenine (A), guanine (G), thymine (T), and cytosine (C). Further examination determined that each species has different proportions of these nucleic acids and in the early 1950s, Austrian born biochemist Erwin Chargraff found that although proportions varied, the amount of (A) was always equal to the amount of (T) and the amount of (G) is always equal to the amount of (C).

      At about the same time, using X-ray diffraction methods, British physicists Rosalind Franklin and Maurice Wilkins showed that DNA casts a shadow resembling a string of overlapping (Xs). This shape and the relationship of (A) to (T) and (G) to (C) suggested to American geneticist James Watson and British biophysicist Francis Crick that DNA had the shape of a twisted ladder (double helix) and in 1953 they constructed a large wire model of the suggested molecule and it became clear that couplings of (A-T) (T-A) and (G-C) (C-G) were rungs on the ladder. Crick and Watson also noted that their model fulfilled the features of a hereditary molecule in that the rungs, A-T, G-C etc. could be cut, leaving a single genetic letter attached to each side of the dissected ladder and new sides could be replicated to replace the missing sides by growing the appropriate paired letter to create two identical ladders. To confirm these findings and conclusions American geneticists Matthew Meselson and Franklin Stahl grew bacterial cells in the presence of heavy atoms of nitrogen so that both sides of their experimental hereditary ladders used only heavy nitrogen in the formation of the bacteria’s nucleotides. They then placed the bacteria in a medium of normal nitrogen and as the bacteria reproduced they used the normal nitrogen to form the missing sides of each ladder. As expected, the new bacteria contained equal amounts of heavy and normal hydrogen supporting the hypothesized replication process.

     Attempts to answer questions related to heredity have been ongoing since ancient times. Aristotle foreshadowed evolutionary thought when he wrote;

    “…and in like manner as to other body parts in which there appears to exist an adaptation to an end and all the parts of one whole happened as if they were made for the sake of something and have been preserved by having been appropriately constituted by an internal spontaneity and further that things not thus constituted have perished and will continue to perish.”

      Philosophy, science and religion have all contributed to the development of genetic theory and continuing investigations have expanded into numerous sub areas of practical application and further research. Classical genetics now includes; microbial genetics, population genetics, cytogenetics, molecular genetics, genomics, human genetics, behavior genetics, epigenetics, and applied genetics in medicine, agriculture and industry.

     Genetics is now out of the box and cannot be put back without dismantling civilization itself.

We now know that every living form contains its own unique coded description, that the language is the same for bacteria, plants and animals, and that all life has a common heritage and that life’s code is passed from generation to generation ready to be translated by RNA into proteins that make up all multi-cellular structures.

     From atoms comes the chemistry of life, from the chemistry of life comes the coded word, from the coded word comes living form, and from the living form, Awareness.