Note the relationship between the first two words and suggest a suitable word for the 4th place.
a. Purines - Adenine and guanine :: Pyrimidines -
b. AUG - Methionine :: AUC -
c. Operon concept - Jacob and Monod :: One gene one enzyme theory -
d. DNA - Thymine and cytosine :: RNA -
e. AUG - initiation codon :: UAA -
f. Xeroderma pigmentosum - Skin cancer :: Retinoblastoma -
g. Semiconservative method of DNA replication - Watson and Crick :: Transformation experiment -

Explanation

a. Cytosine and thymine
b. Isoleucine
c. George Beadle and Edward Tatum
d. Cytosine and uracil
e. Termination codon
f. Cancer of eye
g. Frederick Griffith