SCIENTISTS

Observed chromosome behavior during meiosis using sea urchins (Boveri) and grasshoppers (Sutton); compared with Mendel's laws. DISCOVERED CHROMOSOMAL THEORY OF INHERITANCE.

In 1928, Griffith conducted experiments with Streptococcus pneumoniae using two strains: the virulent smooth (S) strain and the non-virulent rough (R) strain. He found that mice injected with live R strain and heat-killed S strain died of pneumonia, and live S strain bacteria were recovered. This demonstrated that the R strain was transformed into the virulent S strain by some "transforming principle" from the dead S bacteria. Although Griffith did not identify the substance responsible, his work revealed the phenomenon of bacterial transformation.i

Used enzymes to isolate DNA, RNA, and proteins to identify the "transforming principle" in Griffith's experiments. Concluded that DNA is the molecule responsible for heredity and transformation in bacteria.

<p>Analyzed DNA from various organisms and measured base pair ratios. Established Chargaff's rules: the amount of adenine equals thymine, and cytosine equals guanine.</p> Signup and view all the answers

<p>Used radioactive labeling (phosphorus for DNA, sulfur for proteins) in bacteriophages to identify the genetic material transferred to bacteria. Confirmed that DNA is the genetic material in viruses and cells.</p> Signup and view all the answers

<p>Used X-ray crystallography to capture detailed images of DNA fibers, including the famous &quot;Photo 51.&quot;Provided critical evidence of DNA's helical structure and its dimensions.</p> Signup and view all the answers

<p>Built models based on Franklin's X-ray data and Chargaff's rules to propose the double-helix structure of DNA.</p> Signup and view all the answers

<p>Performed isotope labeling experiments with nitrogen (N-15 and N-14) to study DNA replication in E. coli. Demonstrated that DNA replication is semi-conservative, with one parental and one new strand in each daughter molecule.</p> Signup and view all the answers