Calvin Bridges 1889-1938

Calvin Bridges is, with Alfred Sturtevant, one of my heroes of Drosophila genetics.  Among his achievements were the demonstration and confirmation of the chromsome theory of inheritance, and the establishment of the polytene chromosome maps (for more about polytene chromosomes, see this article).  Bridges was one of the early members of the Morgan fly lab, and stayed there for his entire (though unfortunately short) career.  Kohler, in his excellent history of Drosophila genetics, characterises Bridges as the "blue collar" member of the lab, the worker who would invest huge energy in the technical development of Drosophila genetics.

It was Bridges who:

• devised a standard fly medium of cornmeal-agar-molasses (originally the flies were maintained ona banana mush)
• devised Drosophila incubators
• established the Drosophila Information Service (DIS)

Bridges' PhD thesis was on "Non-disjunction as proof of the chromosome theory of heredity", and was published as the first article in the first issue of the journal Genetics.   He is best remembered for his polytene chromosome maps.  Polytene chromosomes are rather peculiar structures, first recognised by Balbiani in the 19th century, which at first sight don't really look like chromosomes.  They are formed by the repeated replication of chromosomes (endoreduplication), where all the copies stay synapes in precise alignment.  In the case of the third instar salivary gland cells, the level of endoreduplication is of the order of 1000x.  The resulting structures display a reproducible banding pattern: this forms the basis of Bridges' inspired chromosome maps.  In fact Bridges wasn't the first to use polytene chromosomes for genetic mapping: Theophilus Painter mapped chromosome inversions in a paper in Science in 1933.  However, it wasn't until Bridges devised his mapping system that Drosophila resarchers the world over could unambiguously refer to specific loci on the polytene chromosomes. These maps were published in 1935, and are still key in rsearch today. 

Bridges had a somewhat unconventional lifestyle (some would say "flamboyant").  He left his wife and family  to pursue "free love", in which his main strategy was apparently to do a lot of propositioning.  This of course led him into some complicated scrapes, some of which are described in Kohler's "Lords of the Fly": Kohler says "he was famous for his flamboyant lifestyle; he left his wife and children in the mid-20s (but continued to support them), got a batchelor pad and a vasectomy; propositioned every woman he met, indiscriminately... his extraordinary good looks and innocence were irresistible" (Kohler 1994 p113).

In the 1925 catalogue of 365 Drosophila mutants, Bridges was responible for the discovery of about two thirds.  Indeed Hermann Mullert remarked that Bridgeswas so prolific a mutant discoverer because he set up and scored as many crosses as all the other lab members combined!

Below: Calvin Bridges in the Carnegie Fly Lab.  Note the "totem pole", on which the genetic maps were assembled, behind him.

Bridges' paper on chromosome theory from 1916, published in Genetics. This appears to be freely available.

Bridges' polytene chromosome map: Bridges (1935) Salivary Chromosome Maps: With a Key to the Banding of the Chromosomes of Drosophila melanogaster.  J. Hered., February 1935; 26: 60 - 64. Link to PDF It appears that a subscription is required to view this classic paper.  Shame on the journal.  The paper is 73 years old, and it's 50 years since Bridges died.  These old and classic papers in journals should not be restricted in this way.