Bacteria Are Grown in a Medium Containing ¹⁵NH₄Cl for a Number

question 79

Multiple Choice

Bacteria are grown in a medium containing ¹⁵NH₄Cl for a number of generations so that all of the DNA is made of fully "heavy" DNA.The bacteria are moved to a new medium and grown in ¹⁴NH₄Cl so that all new DNA will be "light".If replication were dispersive,what would the DNA look like after two generation times.

• A)All of the DNA is made of 2 "light" strands.
• B)Half of the DNA is made of 2 "light" strands and half of the DNA is made of 1 "light" strand and 1 "heavy" strand.
• C)All of the DNA is made of 1 "heavy" strand and 1 "light" strand.
• D)Each strand is made of a mixture of "heavy" and "light" DNA,with each strand being between 75% and 100% "light".
• E)75% of the DNA is made of 2 "light" strands and 25% of the DNA is made of 2 "heavy" strands.

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