James Watson and Francis Crick not only discovered the double helix, but they built the first model too. Although they are sometimes solely accredited for the discovery, they received substantial help from Rosalind Franklin, whose X-ray crystallography images were vital to the discovery.
http://www.answers.com/Q/Which_scientists_developed_the_double_helix_model_of_the_DNA_molecule
One of the ways that scientists have elaborated on Watson and Crick's model is through the identification of three different conformations of the DNA double helix. In other words, the precise geometries and dimensions of the double helix can vary.
http://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397
The DNA double helix polymer of nucleic acid, held together by nucleotides which base pair together. In B-DNA, the most common double helical structure found in nature, the double helix is right-handed with about 10–10.5 base pairs per turn. This translates into about 20-21 nucleotides per turn. The double helix structure of DNA contains a major groove and minor groove.
https://en.wikipedia.org/wiki/Double_helix
The structure of part of a DNA double helix. Chemical structure of DNA. The phosphate groups are yellow, the deoxyribonucleic sugars are orange, and the nitrogen bases are green, purple,pink, and blue. The atoms shown are: P=phosphorus O=oxygen N=nitrogen H=hydrogen.
https://simple.wikipedia.org/wiki/DNA
Now, for the first time, humans have captured direct photos of DNA. Discovery News reports Enzo di Fabrizio, a researcher at the University of Genoa, Italy, has developed a technique that pulls strands of DNA between two miniscule silicone pillars, then photographs them via an electron microscope.
http://www.huffingtonpost.com/2012/12/02/dna-photo-double-helix_n_2219803.html
However, two scientists got the  credit for discovering the double helix sh…ape of DNA, James Watson  and Francis Crick. Watson and Crick get the credit for discovering  the double helix shape because Rosalind Franklin died in 1958, and  the first Nobel prize for discovery wasn't awarded until 1962.
http://www.answers.com/Q/Which_scientists_developed_the_double_helix_model_of_the_DNA_molecule
Many people believe that American biologist James Watson and English physicist Francis Crick discovered in the 1950s. In reality, this is not the case. Rather, DNA was first identified in the late 1860s by Swiss chemist Friedrich Miescher.
http://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397
Chargaff's realization that A = T and C = G, combined with some crucially important X-ray crystallography work by English researchers Rosalind Franklin and Maurice Wilkins, contributed to Watson and Crick's derivation of the three-dimensional, double-helical model for the structure of DNA.
http://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397
DNA Photo Shows Double Helix For The First Time (PHOTOS) We've sequenced it, modified it for our food, and built billion-dollar companies on it. But until now, no one has ever seen a photograph of it. It, of course, is our genetic code, stored along strands of DNA and structured in a double helix. In 1953, when James Watson and Francis Crick first devised DNA's famous shape, they relied heavily on theory, intuition, and Photo 51, a vague image of DNA produced by x-ray diffraction.
http://www.huffingtonpost.com/2012/12/02/dna-photo-double-helix_n_2219803.html
DNA, short for deoxyribonucleic acid, is the molecule that contains the genetic code of organisms. This includes animals, plants, protists, archaea and bacteria. DNA is in each cell in the organism and tells cells what proteins to make. Mostly, these proteins are enzymes.
https://simple.wikipedia.org/wiki/DNA
who developed the first double helical model of dna?
The first double helical model of DNA was developed by James Watson and Francis Crick. James Watson and Francis Crick developed the first double helical model of DNA.   James Watson and Francis Crick developed the first double helical model of DNA. 