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Q14(b):
Briefly describe the following:
Polymorphism
Solution :
Definition and Theoretical Framework
In the context of molecular genetics, Polymorphism refers to the occurrence of two or more clearly different phenotypes or genetic variants (alleles) within a population at a frequency greater than 0.01 (or 1%) [Per the Hardy-Weinberg equilibrium principle for population genetics]. Unlike rare mutations, which are sporadic, polymorphisms are stable and contribute to the genetic diversity that facilitates evolutionary adaptation.
Step 1: Molecular Basis of Polymorphism
At the genomic level, polymorphism arises due to mutations in non-coding sequences of DNA. These mutations accumulate over generations because they do not code for proteins and are not subjected to immediate natural selection [Per the Neutral Theory of Molecular Evolution]. These variations include:
- Single Nucleotide Polymorphisms (SNPs): Variations at a single position in a DNA sequence among individuals.
- Variable Number Tandem Repeats (VNTRs): Short nucleotide sequences arranged in tandem, where the number of repeats varies between individuals.
Step 2: Analytical Significance (DNA Fingerprinting)
The high degree of polymorphism in non-coding, repetitive DNA sequences, specifically Satellite DNA, is the foundation for DNA profiling. The steps are summarized below:
| Mechanism | Process |
|---|---|
| Isolation | Extraction of genomic DNA from the sample. |
| Digestion | Cleavage of DNA using Restriction Endonucleases at specific recognition sites. |
| Separation | Electrophoretic separation based on length polymorphism (size). |
| Hybridization | Transfer to a membrane (Southern Blotting) and probing with radioactive VNTR probes. |
Step 3: Visual Representation of DNA Length Polymorphism
The following SVG illustrates how two individuals (A and B) exhibit different banding patterns on an electrophoresis gel due to varying lengths of repetitive sequences.
Step 4: Inheritance and Population Dynamics
Polymorphisms are inherited from parents to offspring according to Mendelian laws. Because these sequences (VNTRs) are highly polymorphic, the probability of two individuals (excluding monozygotic twins) having the same pattern is virtually zero. This confirms that polymorphism is an inheritable mutation that allows for the precise identification of biological samples [Per the Principles of Forensic Molecular Biology].
Final Solution: Polymorphism is defined as the existence of genetic variation within a population at a frequency exceeding 1%, resulting from heritable mutations in non-coding DNA, specifically utilized in DNA fingerprinting due to its high level of individual-specific variability.
More Questions from Class 12 Biology Molecular Basis of Inheritance EXERCISES
- Q1: Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine.
- Q1: Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine.
- Q2: If a double stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA.
- Q2: If a double stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA.
- Q3: If the sequence of one strand of DNA is written as follows: 5' -ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of complementary strand in 5'\(\rightarrow\)3' direction.
- Q3: If the sequence of one strand of DNA is written as follows: 5' -ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of complementary strand in 5'→3' direction.
- Q4: If the sequence of the coding strand in a transcription unit is written as follows: 5' -ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of mRNA.
- Q4: If the sequence of the coding strand in a transcription unit is written as follows: 5' -ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of mRNA.
- Q5: Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.
- Q5: Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.
- Q6: Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesised from it (DNA or RNA), list the types of nucleic acid polymerases.
- Q6: Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesised from it (DNA or RNA), list the types of nucleic acid polymerases.
- Q7: How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?
- Q7: How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?
- Q8(a): Differentiate between the followings: Repetitive DNA and Satellite DNA
- Q8(a): Differentiate between the followings: (a) Repetitive DNA and Satellite DNA
- Q8(b): Differentiate between the followings: mRNA and tRNA
- Q8(b): Differentiate between the followings: (b) mRNA and tRNA
- Q8(c): Differentiate between the followings: Template strand and Coding strand
- Q8(c): Differentiate between the followings: (c) Template strand and Coding strand
- Q9: List two essential roles of ribosome during translation.
- Q9: List two essential roles of ribosome during translation.
- Q10: 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?
- Q10: 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?
- Q11(a): Explain (in one or two lines) the function of the followings: (a) Promoter
- Q11(a): Explain (in one or two lines) the function of the followings: Promoter
- Q11(b): Explain (in one or two lines) the function of the followings: (b) tRNA
- Q11(b): Explain (in one or two lines) the function of the followings: tRNA
- Q11(c): Explain (in one or two lines) the function of the followings: (c) Exons
- Q11(c): Explain (in one or two lines) the function of the followings: Exons
- Q12: Why is the Human Genome project called a mega project?
- Q12: Why is the Human Genome project called a mega project?
- Q13: What is DNA fingerprinting? Mention its application.
- Q13: What is DNA fingerprinting? Mention its application.
- Q14(a): Briefly describe the following: (a) Transcription
- Q14(a): Briefly describe the following: Transcription
- Q14(b): Briefly describe the following: (b) Polymorphism
- Q14(c): Briefly describe the following: (c) Translation
- Q14(c): Briefly describe the following: Translation
- Q14(d): Briefly describe the following: (d) Bioinformatics
- Q14(d): Briefly describe the following: Bioinformatics
CBSE Solutions for Class 12 Biology Molecular Basis of Inheritance
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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