Class 12th Biology 2016 Set1 Delhi Board Paper Solution
Describe the experiment that helped demonstrate the semi-conservative mode of DNA replication.
Semi-conservative DNA replication:
The two Strands would separate and act as a template for the synthesis of new complementary strands. After the completion of replication, each DNA molecule would have one parental and one newly sytnthesized strads this scheme was termed as semi-conservative DNA replication.
Who Found:
In 1958 Meselson and Stahl's proved the semi-conservative mode of replication.
Experiment:
They worked with E. coli using a heavy isotope of Nitrogen, 15N E. coli was grown with 15N for several generation till the bacteria become completely labelled with 15N. They were then shifted to medium with normal 14N nitrogen sample were taken after every genereation and tested for the presence of 15N and 14N using density gradiant centrifugation with CsCI the first generation was found be hybrid between 15N and 14N second generation contain tow types of DNA, 50% light (14N) and 50% intermediate. This is only possible if two strands separate during replication and act as a template for synthesis of new complementary strands, thus proving a semiconservative mode of replication.
Observation:
Since E. coli divides every 20 minutes, the DNA extracted after 20 minutes experiment had a hybrid density.
The DNA extracted after 40 minutes had equal amounts of hybrid and light densities.
Popular Questions of Class 12th biology
- Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
- Q:- Why is reproduction essential for organisms? Answer
- Q:- Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals. - Q:- With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
- Q:- What is DNA fingerprinting? Mention its application.
- Q:- What is oogenesis? Give a brief account of oogenesis.
- Q:- Describe the structure of a seminiferous tubule.
- Q:- What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
- Q:- With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
- Q:- Explain the Law of Dominance using a monohybrid cross.
Recently Viewed Questions of Class 12th biology
- Q:- Name the functions of the following.
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae - Q:- Write two major functions each of testis and ovary.
- Q:- Do you think microbes can also be used as source of energy? If yes, how?
- Q:- Define and design a test − cross?
- Q:- How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
- Q:- Discuss with your teacher what does a suitable gene means, in the context of DNA vaccines.
- Q:- Discuss with your teacher and find out how to distinguish between
(a) Plasmid DNA and chromosomal DNA
(b) RNA and DNA
(c) Exonuclease and Endonuclease - Q:- In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?
- Q:- Differentiate between gametogenesis from embryogenesis.
- Q:- How does the transmission of each of the following diseases take place?
(a) Amoebiasis
(b) Malaria
(c) Ascariasis
(d) Pneumonia