1) Beadle and Tatum's experiment using bread mold Neurospora showed that each gene encodes the structure of one polypeptide, supporting the "one gene, one enzyme" hypothesis. 2) Meselson and Stahl's experiment using radioisotope labeling of DNA demonstrated that DNA replication occurs via the semi-conservative model, where each new DNA molecule contains one original and one newly synthesized strand.

1. 1)Beadle & Tatum’s Experiment - Using bread mold neurospora to show each gene encodes the structure of one polypeptide. 2)Meselson & Stahl’s Experiment - Using the radioisotope labeling technique to show the semi-conservative model of DNA replication

2. 4.1.3 Gene concept; one gene one polypeptide George Beadle and Edward Tatum experiment: connection between genes & metabolism. Neurospora crassa as experimental organism. - short life-cycle, easily grown. Since it is haploid for much of its life cycle, mutations would be immediately expressed.

3. Gene concept; one gene one polypeptide Neurospora crassa able to synthesize all of the amino acids and other chemicals needed for growth mutations will affect a single genes and single enzymes in specific metabolic pathways.

4. Chemical reactions occurring in the body mediated by enzymes (proteins) Heritable traits- must be a relationship between the gene and proteins. Beadle and Tatum proposed the " one gene one enzyme " theory. Gene concept; one gene one polypeptide

5. One gene, one polypeptide One gene codes for one protein. "One gene one enzyme" modified to " one gene one polypeptide " since many proteins made of more than one polypeptide Biosynthesis of amino acids: complex chemical reactions mediated by enzymes, which if mutated- shut down the pathway no growth.

7. 4.2 DNA Replication Watson and Crick Model of DNA suggest that each strand of DNA molecule could serve as a template, for the synthesis of the opposite strand. Each half-helix could pair with their complementary nucleotides to replace its missing partner. The result would be two DNA double helices, each identical to the original. Definition : Process of copying a double stranded DNA strand which is the two resulting double strands are identical and each of them consist of one original and one newly synthesize strand.

8. 3 hypothesis that told about DNA replication :- CONSERVATIVE both parent (or old) strand remain together and an all new copy is made SEMICONSERVATIVE the 2 strand of the parental molecule separate and each functions as a template for synthesis of a new complementary strand DISPERSIVE each strand of both daughter molecules contains a mixture of old and newly synthesized parts

10. In 1958, Meselson and Stahl studied the replication of E.Coli . Meselson and Stahl Experiment Hypothesis : DNA replication are take place by semiconservative mechanism

14. Conclusion Hypothesis are accepted. Experiment approved that DNA replication are take place by semiconservative.