NCERT Class 12 Biology: Chapter –6 Molecular Basis of Inheritance Part 5

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Question 7:

Based on your understanding of genetic code, explain the formation of any abnormal haemoglobin molecule. What are the known consequences of such a change?

Answer:

1. This abnormal haemoglobin molecule formation occurs because one codon GAG gets replaced by GUG. Which means in the codon GAG adenosine gets replaced by uracil.

2. This change leads to the incorporation of valine in the beta haemoglobin chain instead of Glutamic acid at the 6th position. This mutation changes the shape of red blood cell from disc shaped to sickle shape that is why it is also known as Sickle cell anaemia.

3. These sickle shaped blood cells have shorter life span than the normal blood cells. Sometimes they also get stuck in the arteries and causes blockage in the blood flow.

4. The following change may cause the death of the individual before attaining maturity.

Question 8:

Sometimes cattle or even human beings give birth to their young ones that are having extremely different sets of organs like limbs/position of eye(s) etc. Comment.

Answer:

Sometimes cattle or even human beings give birth to their young ones that are having extremely different sets of organs like limbs/position of eye(s) etc. It happens due to uncoordinated regulation of gene expression in the gene sets associated with organ development.

Question 9:

In a nucleus, the number of ribonucleoside triphosphates is 10 times the number of deoxy x10 ribonucleoside triphosphates, but only deoxy ribonucleoside are added during the DNA replication. Suggest a mechanism.

Answer:

The number of ribonucleoside triphosphates is 10 times the number of deoxy ribonucleoside triphosphates, but only deoxy ribonucleotides are added during the DNA replication because:

1. The enzyme DNA polymerase only recognises deoxyribonucleotides triphosphates.

2. It incorporates the same as deoxy ribonucleotides during DNA replication.

Question 10:

Name a few enzymes involved in DNA replication other than DNA polymerase and ligase. Name the key functions for each of them.

Answer:

The few enzymes involved in DNA replication other than DNA polymerase and ligase are:

1. Helicases: These are the enzymes which separate the two DNA strands at the replication fork using energy. These enzymes are also called as helix destabilizing enzyme.

2. DNA Clamp: This enzyme is used to promote the replication of the DNA. It binds the DNA polymerase enzyme to the template strand and prevents it from disassociating. It is also known as sliding Clamp.

3. Single Strand Binding Proteins: These enzymes prevent the single strand of DNA to get digested by the nucleases. It also prevents the formation of secondary structure.

Question 11:

Name any three viruses which have RNA as the genetic material.

Answer:

The three viruses which have RNA as the genetic material are:

1. Tobacco Mosaic Virus

2. Human- Immuno Deficiency Virus

3. Influenza Virus

Short Answer Type Questions

Question 1:

Define transformation in Griffith’s experiment. Discuss how it helps in the identification of DNA as the genetic material.

Answer:

1. The experiment was performed in the year 1928 by Frederick Griffith.

2. Griffith used two strains of bacteria Streptococcus Pneumoniae.

3. These were the S-strain (smooth strain) and the R-strain (rough strain) .

4. These strains were then injected into two different mice.

5. He found that only mice injected with S-strain had the disease and was virulent. This was because the S-strain has a polysaccharide covering which protected the strain from mice’s immune system.

6. The R--strain mice did not have the disease and was non-virulent. This was because the R-strain did not have the covering which protected the strain from mice’s immune system.

7. After this, a combination of heat killed S-strain and live R-strain were injected into two different mice.

8. The disease was seen in the mice.

9. Through this Griffith showed that the transformation took place.

10. Some ‘transforming principle’ of the S-strain was picked up by the R-strain which transformed the R-strain to the S-strain and made it virulent. This change in R-strain showed that it was the inherited genetic material.

11. This genetic change was permanent which further showed that DNA was the genetic material.

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