NEET Botany Molecular Basis of Inheritance Questions Solved


Escherichia coli cells were grown for many generations in 15NH4Cl as sole nitrogen source. Subsequently, these cells were grown exactly for four generations in medium containing 14NH4Cl. The DNA from these cells were isolated and separated. If 15N/15N represents the two strands of DNA where both strands have heavy nitrogen; 15N/14N as intermediate DNA; and 14N/14N as DNA containing light nitrogen, the ratios for heavy: intermediate: light DNA, respectively would be:

(a) 1 : 0 : 7          (b) 1 : 1 : 6          (c) 0 : 1 : 7           (d) 0 : 8 : 0

According to semiconservative mode of DNA replication :

Generation

 

Heavy DNA

Intermediate DNA

Light DNA

Parental

1

-

-

I

-

2

-

II

-

2

2

III

-

2

6

IV

-

2

14

Ratio = 0 : 2 : 14 = 0 : 1 : 7

(page-105)

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