Molecular Basis of Inheritance Question 96

96. If a completely radioactive double stranded DNA molecule undergoes two rounds of replication in a non-radioactive medium, what will be the radioactive status of the four resulting molecules?

[1997]

(a) Half the number contain no radioactivity

(b) All four still contain radioactivity

(c) Three out of four contain radioactivity

(d) Radioactivity is lost from all four

Show Answer

Answer : a

Hints & Solution

(a) DNA replication is semiconservative. i.e. at each replication one of the parental strands is retained and a new daughter strand is obtained. Thus only half of the parental DNA molecule is carried to the next generation. $\longrightarrow{$ radioactive DNA