CONTRIBUTION OF A,H STURTEVANT ,C.B BRIDGES AND H.J MULLER.

• T.H MORGAN done his studies of Heredity on Drosophilla and was soon joined in the famousfly room at Colombia University by three principal students A.H STURTEVANT ,C.B BRIDGES and H.J MULLER.

• Within the space of 5 years ,they formulated a revolutionary 'CHROMOSOME THEORY OF HEREDITY'.

• Their accomplishment ,which led to Morgan wining the Noble prize in 1933 are all more remarkable because their sole experiment method was to do controlled crosses  with these mutants and count progeny.

• In 1913 Sturtevant constructed the first genetic map and showed that genes are arranged in a linear order in 1920.                                                                                                                             
• His major contribution was his introduction to the concept that the frequency of crossing over between two genes could help determine their proximity on a linear genetic map.

• His work also helped to determine gene role in sexual  selection and development and  displayed importance of crossing over in mutation.

• He also got National Medal of Science in 1967 for his work.

• In 1914 and 1916 BRIDGES  published two papers .Bridges exploiting Chromosome non -disjunction  in XXY females ,provided the first elegant proof that chromosomes must contain genes ;this ruled out the alternative possibility assumed by some at the time ,that the Chromosome and genes were seperate hereditary material.                                                                    
• Bridges published many works, one of his famous being 'Sex in relation to Chromosome and Genes'.

• In 1935 and 1938  Bridges published polytene maps of such accuracy that they are still used today .Making extensive use of chromosomal rearrangements .                                                        
• Bridges also constructed cytogenetic maps that assigned genes to specific sections and even bands.

• In 1918 MULLER introduced the use of balancers Chromosome,bearing inversions that allow the stable maintainance of lethal mutations as heterozygotes in a manner that doesn't require selection ,this is only now that it has become in the nematode and is still not possible in mice.                 
•  He is best known for his work on the physiological and genetic effect of radiation  (Mutagenesis).

• It was in year 1927, Muller showed that the ionising radiation causes the genetic damage and that mutation including chromosomal rearrangements ,can be induced with X-rays ,a finding for which  he got Noble prize in 1946 .