Important Questions for Class 12 Chapter 6: Molecular Basis of Inheritance

Genes are the basic unit of heredity. Most of the genes comprises strands of genetic material called DNA. DNA comprises all the hereditary information of an individual. This information is passed on from one generation to the other in the form of homologous chromosomes. The DNA is transcribed into mRNA and translated into proteins. This is known as central dogma.

Explore important questions on the Molecular Basis of Inheritance for a better understanding of the concept.

Very Short Answer Type Questions

Q.1. State the function of histones in DNA packaging.

A.1.

• They play a role in gene regulation.
• They help the DNA to wind around it.
• The histones are positively charged proteins, which can easily bind to the negatively charged DNA.

Also Read DNA packaging.

Q.2. What is the difference between heterochromatin and euchromatin?

A.2.

Heterochromatin is a tightly packed DNA, which can be identified when stained in an extreme nuclear stain.

Euchromatin is a lightly packed DNA, which can be identified when stained in a less nuclear stain.

More Details: Difference between heterochromatin and euchromatin

Q.3. Name any three viruses with RNA as the genetic material.

A.3. The viruses in which the genetic material is RNA is called the RNA virus. The three examples of the RNA virus.

1. Influenza Virus.
2. Hepatitis C Virus.
3. Human Immunodeficiency Virus.

Explore More: Virus

Q.4. Give a reason for the discontinuous synthesis of DNA on one of the parental strands?

A.4. The biological process of DNA synthesis naturally occurs in 5′ to 3′ direction. In the double-stranded DNA, the strands are parallel and antiparallel to each other. During the synthesis of DNA, both the strands act as templates and only one (3′ to 5′ direction) can synthesize the parallel strand in 5’→3′ direction. The other strand 5′ to 3′ is synthesized in the opposite direction producing small stretches of DNA known as Okazaki fragments. This is the reason for the discontinuous synthesis of DNA on one of the parental strands.

Q.5. The sequence of the coding strand of DNA in a transcription unit is mentioned below.

3′ AATGCAGCTATTAGG 5′

Write the sequence for:

1. Its complementary strand
2. Its mRNA

A.5.

1. The complementary strand is  5′ TTACGTCGATAATCC 3′
2. The mRNA is  5′ AAU GCAGCUAUUAGG 3′

Q.6. What is DNA polymorphism?

A.6. DNA’s polymorphism is the variation in the DNA sequence arising due to mutation at non-coding sequences.

Q.7. Retroviruses do not follow central dogma.  Comment on this statement

A.7. Retroviruses do not follow central dogma, because, they possess RNA as genetic material instead of the DNA, which is later converted into DNA by the enzyme reverse transcriptase.

Explore more: Retroviruses

Q.8. Sometimes, the young ones born have an extremely different set of eyes or limbs. Give a relevant explanation for the abnormality.

A.8. This abnormality is caused by many factors, including alcohol abuse by the mother during her pregnancy, medicine side effects or reactions caused to the womb,  environmental factors, such as maternal exposure to the chemicals, radiations, virus, and it can also be due to the genes and non-coordination in the regulation of expression in the set of genes associated with the development of organs.

Q.9. Explain about the dual polymerase present in E.coli.

A.9. The DNA polymerase present in E.coli is a DNA dependent polymerase. This DNA polymerase helps in the:

1. Replication process.
2. Performs the 5′ to 3′ polymerase activity as well as 3′ to 5′ exonuclease activity.
3. The DNA polymerase III also has the ability to proofread the wrong nucleotides and substitutes it with the correct one.

Q.10. What are the functions of the :

1. Methylated guanosine cap
2. Poly-A tail

A.10.

1. Methylated guanosine cap plays a primary role in the attachment of the mRNA to the smaller sub-units of the ribosome during translation initiation.

2. The Poly-A tail functions by increasing the length of the mRNA and also provides longevity to the mRNA.

Q.11. Mention any two functions of AUG codon.

A.11. The AUG codon is also called the start codon. The two important functions of AUG codon include:

1. It codes for methionine.
2. It acts as an initiation codon for protein synthesis.

Q.12. What is the function of amino acyl t-RNA synthase?

A.12. Amino acyl t-RNA synthase plays a major role in the biosynthesis of proteins by attaching an appropriate amino acid on to the tRNA molecules.

Long Answer Type Questions

Q.1. Enumerate the post-transcriptional modifications in a eukaryotic mRNA.

A.1. Transcription is the process of conversion of DNA to mRNA. The post-transcriptional modifications include:

• Capping at 5’-end
• Poly-A tail at 3’-end
• mRNA splicing

The 5′ cap protects the RNA from ribonuclease. The poly-A tail protects the mRNA from enzymatic degradation. The introns are spliced during mRNA splicing and the exons are joined together to form a continuous sequence that codes for a functional protein.

Refer more: Transcription

Q.2. Explain the process of translation.

A.2. The translation is the process of protein synthesis in which the mRNA is used to synthesize proteins. The mRNA sequence is decoded to specify the amino acid of a polypeptide. The process of translation is carried out in the following steps:

• Initiation.
• Elongation.
• Termination.

Also Read: Translation

Q.3. Explain the process of DNA fingerprinting.

A.3. DNA fingerprinting is a technique that is used to analyze the genetic makeup of living beings. It is widely used for DNA analysis in forensic tests and paternity tests to identify the biological parents of the child, and also to identify the criminal during forensic investigations.

Extended Reading: DNA fingerprinting

Q.4. What is an operon? Explain an inducible operon.

A.4. An operon is the functional unit of DNA that contains a cluster of genes controlled by a single promoter. It consists of the following components:

• The DNA fragment that transcribes the mRNA.
• Regulator gene that codes for a repressor protein.
• Inducer that prevents the repressor from binding to the operator.
• A promoter where the RNA polymerase binds and initiates the transcription.
• An operator that is a DNA sequence adjacent to the promoter where the repressor protein binds.

The lac operon of E.coli is an inducible operon.

Q.5. Explain the process of DNA replication.

A.5. DNA replication is a biological process of producing two identical strands of DNA from the original strand. The original strand is known as the parent strand and the new strands are known as the daughter strands. This is achieved by a number of enzymes such as DNA polymerase, helicase, primase, topoisomerase, and ligase.

Read More: DNA replication

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