E coli bacteria divides in every 20 min so, in 80 min it will be four generations.
N15 isotopes is present in the environment than shifted in N14 environment, so it will result in the presence of N15 and N14 strands in DNA .
In the second generation, half will have the previous hybrid bacteria and half will have the light bacteria.
In the third generation, hybrid generation will again cut half , this time 25% hybrid and 75% light.
In fourth generation, 16 copies will be hybrid and 14 will be light.


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Introduction:
E. coli is a bacteria commonly used in scientific research due to its fast growth and well-studied genetics. The replication of DNA in E. coli follows a specific pattern, resulting in two distinct densities of DNA molecules: light and hybrid.

Explanation:
When E. coli is allowed to grow for 80 minutes, the DNA replication process occurs, resulting in the formation of light and hybrid density DNA molecules.

Light density DNA:
During DNA replication, the two strands of the double helix separate, and each strand serves as a template for the synthesis of a new complementary strand. This process is known as semi-conservative replication. In the early stages of DNA replication, the newly synthesized strands are lighter in density compared to the parental strands.

Hybrid density DNA:
As DNA replication progresses, the newly synthesized strands gradually become more heavy in density. This is because the parental strands serve as templates for the synthesis of new strands, leading to a mix of old and new DNA strands in each replicated chromosome. These mixed strands are known as hybrid density DNA.

Proportions of light and hybrid densities:
After 80 minutes of growth, the proportions of light and hybrid density DNA molecules in E. coli can be determined. It is important to note that the exact proportions may vary depending on various factors such as the growth conditions and the specific DNA replication dynamics of E. coli.

However, generally, after 80 minutes of growth, a significant portion of the DNA would have undergone replication, resulting in an increased proportion of hybrid density DNA molecules compared to light density DNA molecules. This is because the replication process continues throughout the growth period, leading to the synthesis of new DNA strands and the conversion of light density DNA into hybrid density DNA.

The exact calculation of the proportions would require experimental data and analysis using techniques such as density gradient centrifugation. By separating the DNA molecules based on their densities, the proportions of light and hybrid density DNA can be determined.

Conclusion:
After 80 minutes of growth, the proportions of light and hybrid densities DNA molecules in E. coli would depend on the specific DNA replication dynamics of the bacteria. However, it can be generally expected that a significant portion of the DNA would have undergone replication, resulting in an increased proportion of hybrid density DNA compared to light density DNA. Experimental techniques like density gradient centrifugation can be used to accurately determine these proportions.