Question

if hybrid DNA is allowed to replicate for one generation in medium containing N14 and for second generation in medium containing N15 then what is the proportion of light, heavy and hybrid DNA obtained respectively???

Answer 1

HYBRID MEANS ONE CHAIN OF N14-N15

N14-N15 in N14 medium

N14-N14 and N-15-N14

NOW both in N15 medium

3(N14-N15)and one N15-N15

THE RATIO will be

light=0

heavy=1

hybrid=3

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Answer 2

Answer:

• The proportion of light DNA - Zero
• The proportion of heavy DNA - Zero
• The proportion of hybrid DNA - Two.

Explanation:

N14 is the light isotope and N15 is the heavy isotope of Nitrogen. E.coli is grown in mediums containing N14 and N15 to prove the semiconservative nature of DNA.

Let: -

• Light DNA be at the top
• Hybrid DNA be in the middle
• Heavy DNA be at the bottom.

In the given question, the DNA is already hybrid, i.e., it is found in the middle. Hybrid DNA means that it is a mixture having both N14 and N15.

Then, the DNA is transferred to the N14 medium. Here another light band is produced along with the hybrid one. Thus, now we have a band at the top and another in the middle.

The Second generation is transferred to N15 containing medium. Now the light one will mix with the heavy one produced by N15 and form a hybrid DNA. Thus, in the end, we have two hybrid DNAs.