Rosalind Franklin and Maurice Wilkins conducted experiments using X-ray crystallography to study the structure of the DNA. Their experiments produced the famous photo 51, the first evidence on the structure of the DNA. Their work showed that DNA is double-stranded and forming a helix. They also showed that the nitrogenous bases are on the inside of the strands and that the phosphates are on the outside. Watson and Crick used these observations to develop their model on the molecular structure of the DNA.
The average menstrual cycle is 28 days long but can vary from 24 to 38 days. If a menstrual cycle is shorter, a person can have a period more than once a month.
