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(21.04.2006)
| (a) | Genetic material must be able to enter the next generation, then, it can pass the traits to the next generation. Only the head of the sperm can become part of the zygote. And, the major part of the head of the sperm is the cell nucleus. There is almost no cytoplasm. But the major constituent of the head is DNA. Therefore, DNA would be the genetic material. |
| (b) | If all cells contain the same set of genetic material, then, the amount of genetic material in each cell should be the same. Scientists proved that the amount of DNA in any body cell of the same individual is the same. |
| (c) | Theoretically, the mass of DNA in a diploid cell should be a double of that of the haploid cell. Also, scientist proved that the above hypothesis is true. |
| (d) | Anything that can change DNA should be able to cause change in genetic trait. |
| (A) | Genic transformation Genic transformation is the phenomenon that the bacterial cells can collect DNA from the dead bacterial cells and get the genetic trait. This experiment was conducted in 1928 by Griffith with pneumococcus, or pneumonia diplococcus. There are two strains of pneumococcus, or pneumonia diplococcus. One possesses a slimy capsule, forming smooth colony and causes pneumonia. Another has no capsule, forming rough colonies and cannot cause pneumonia. In 1928, Griffin mixed the cooked, capsulated pathogenic pneumonia diplococcus with the living, non-capsulated non-pathogenic diplococcus. The mixture was then, injected into the bodies of living rats. Several days later, most rats dead of pneumonia. Friffin found the living capsulated pneumonia diplococcus inside the dead rats. This showed that the living non-capsulated, non-pathogenic diplococcus had got some material from the dead capsulated and pathogenic pneumonia diplococcus. So, the non-capsulated diplococcus became capsulated and pathogenic, and caused dead of the rats. |
| (B) | Virus transduction Virus transductiondescribed that a virus can transfer something from bacteria A to bacteria B, if it infected bacteria A, then, bacteria B. When the virus infects bacteria A, it will mix its genetic material with the genetic material of the bacteria. When it leaves the bacteria, it would take aome genes away from the bacteria. So, when it infects another bacteria later, the genes of bacteria A would be transferred into the next bacteria. |
| (C) | Hershey and Chase In 1952, Hershey and Chase used the T2 bacteriophage in their studies. Bacteriophage is a virus parasitic in bacterial cells. They used this T2 bacteriophage to attack Escherichia coli or E. coli, and observed the result. Each bacteriophage would have a protein coat and a nucleoprotein core. In invading cells, only the nucleoprotein core can enter the cell. The protein coat would be left outside. After entering the cell, the nucleoprotein would start to control all biochemical activities of the cell, and start the production of viral proteins and viral nucleoproteins. Then,. virus particles would be assembled. The viral particles would be gradually released, or, all viral particles would be released in a single batch when the cell is exhausted and bursted. In the experiment of Hershey and Chase, two T2 viruses were used. One was labelled with 35S, so, its protein coat became radioactive. Another was labelled with 32P, so, its nucleoprotein core was radioactive. In their experiments, they used these radioactive bacteriophage to infect two different batachs of E. coli. Eventually, they found that the E. coli infected with bacteriophage with radioactive protein coat did not produce similar bacteriophages. But the E. coli infected with bacteriophage with radioactive nucleoprotein core did produce similar bacteriophages. Therefore, they concluded that the nucleoprotein was the genetic material. |
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