Thursday, December 7, 2017

History of Genetics

For thousands of years, humans have acted as agents of genetic selection, by breeding offspring with desired traits. All our domesticated animals (dogs, horses, cattle) and food crops (wheat, corn) are the result.
Yet for most of this time, humans had no idea how traits were inherited.  Why?
Offspring resemble parents (or don't) in bewilderingly complex ways.  That is because individuals in nature contain many genes, and many different versions (alleles) of each gene.  Consider these three individual orchids:

Orchid Photos
  • What happens when you breed them?  Try it out -- Orchid cross.  (To cross, click on one of the orchids.)
In 1866, Gregor Mendel discovered independent assortment of traits, dominant and recessive expression. Traits appear in pairs; separate independently in the gametes; recombine in pairs, in offspring. (Today we know Mendel only studied unlinked traits: on separate chromosomes, or so far apart that crossover frequency approached 50%).
But Mendel's work was lost.  Only in the past century did humans learn the fundamental mechanisms of heredity:
How and why organisms resemble their parents; and how the inherited information functions to make organisms look and behave as they do.

1902 -- Walter Sutton and Theodore Boveri, using dyes synthesized by the German organic chemistry industry, observed that "colored bodies" in cells behaved in ways parallel to the hypothetical agents of heredity proposed by Mendel. These bodies were called chromosomes.1905 -- Nettie Stevens observed in Tenebrio beetles that all pairs of homologous chromosomes are the same size, except for one pair which determines sex -- X, Y.
1909 -- Thomas H. Morgan correlates the X chromosome with sex-linked inheritance of the white eye trait in Drosophila -- a strain of flies discovered by an undergraduate lab assistant, cleaning out old bottles of flies in Morgan's lab. Morgan went on to make many important discoveries in fly genetics and linkage analysis that apply to all diploid organisms.
1941 -- Beadle and Tatum determined in Neurospora that each gene encodes one product (protein). (Later, we learned that RNA can be a product, not always transcribed to protein; for example, a ribosomal RNA.)
1944 -- Oswald Avery identified DNA as the genetic material. Pieces of DNA can transfer genes into bacteria cells, and transform them genetically.
953 -- Rosalind Franklin and Maurice Wilkins showed that DNA is a double helix.
Thomas Watson and Frances Crick determined the structure of the base pairs which enable replication producing two identical daughter helices.1961 -- Jacob and Monod figured out regulation of the lac operon.
1960's -- Barbara McClintockdiscovered transposable elements in corn; later found in bacteria and animals.
1970 -- Temin and Balitimore discovered reverse transcriptase in retroviruses; an enzyme later used to clone genes based on the RNA encoding the product.
1977 -- Maxam, Gilbert, Sanger, others -- developed methods to sequence DNA.
1981 -- The first transgenic mammals were made.
1987 -- Kary Mullis invented the polymerase chain reaction (PCR), using a thermostable enzyme from a thermophilic bacterium discovered by Thomas Brock at a geyser in Yellowstone. Mullis sold the process to a pharmaceutical company, and earned very little. Brock didn't earn a cent.
1995 -- The first bacterial genome sequence, Haemophilus influenzae, was completely determined.
1996 -- Ian Wilmut cloned the lamb Dolly  from adult mammary gland tissue.
2000 --Completion of the human genome
2010 -- Whole organs grown in culture?
2020 -- Chimp/human hybrids demand human rights?

2050 -- Self-aware computers demand human rights?


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