Genetics And Evolutionmolecular Basis Of Inheritance Topic
Molecular Basis of Inheritance 📝
1. Structure of DNA and RNA
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DNA Structure:
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Composition: Deoxyribonucleic acid(DNA) consist of deoxyribose sugar, phosphate group and nitrogenous bases adenine(A), thymine(T), cytosine (C) and guanine(G).
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Double helix: DNA forms a double-stranded helix structure connected by hydrogen bonds between nucleotide bases. -Base pairing: A pairs with T, while C pairs with G, following the Chargaff’s rule.
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Types of RNA:
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Messenger RNA(mRNA): Carries genetic information from DNA to ribosomes for proteins synthesis.
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Transfer RNA(tRNA): Brings specific amino acids to the ribosome based on the mRNA codon during protein synthesis.
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Ribosomal RNA(rRNA): Essential components of ribosomes, catalyzing peptide bond formation during translation.
2. DNA Replication
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The process by which DNA duplicates itself before cell division.
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Key steps:
- Initiation: Begins at specific origin sites of DNA.
- Elongation: DNA polymerases enzyme add complementary nucleotides to the growing strands, following the base pairing rules.
- Termination: Reaches specific termination sequences, signalling the end of replication.
3. Transcription
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The process of synthesizing RNA molecules using DNA as the template.
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Key steps:
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Initiation: RNA polymerase enzyme binds to the promoter region of DNA.
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Elongation: RNA polymerase synthesizes mRNA following the base pairing rules, reading the DNA template from the 5’ (promoter) end towards the 3’ end (terminator).
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Termination: Transcription stops at specific termination signals.
4. Translation
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The process of synthesizing proteins based on the information carried by mRNA.
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Key steps:
- Initiation: Ribosome binds to mRNA at the start codon (usually AUG).
- Elongation: tRNA, with specific amino acids, bind to the mRNA codon, facilitated by the ribosome. Peptide bonds form between successive amino acids.
- Termination: Reaches a stop codon, signalling the end of translation.
5. Gene Expression
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Regulation of gene expression allows cells to control when and where proteins are made.
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Mechanisms:
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Transcriptional: Control gene expression at the level of transcription.
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Translational: Control gene expression by regulating the initiation and elongation steps of translation.
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Post-translational: Control gene expression by modifying proteins after their synthesis.
6. Mutations
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Changes in the DNA sequence, can be caused by errors in DNA replication or exposure to mutagens.
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Types:
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Substitutions: Replacement of one nucleotide with another.
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Insertions: Insertion of additional nucleotide(s) into the sequence.
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Deletions: Removal of one nucleotide(s) from the sequence.
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Frameshift: Insertion or deletion that alters the reading frame, leading to incorrect amino acid sequence.
7. Genetic Code
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The set of rules that determines how nucleotide triplets (codons) in mRNA correspond to specific amino acids during translation.
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Properties:
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64 codons: Three stop codons (UAA, UAG, and UGA) signals the end of translation, while the remaining 61 codons specify amino acids.
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Degenerate: Multiple codons can code for the same amino acids.
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Wobble hypothesis: Some tRNA contain modified nucleotides that can recognize multiple codons.
8. DNA Repair Mechanisms
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Cellular mechanisms that identify and repair damages in DNA.
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Types:
- Base excision repair: Repairs damages like oxidized or methylated bases.
- Nucleotide excision repair: Removes damaged nucleotides along with surrounding nucleotides.
- Mismatch repair: Corrects errors during DNA replication.
9. Recombination
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Process of exchanging genetic material between homologous chromosomes during meiosis.
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Types: -Crossing-over: Exchange of genetic material between non-sister chromatids. -Gene conversion: Non-reciprocal transfer of genetic material from one chromosome to its homologue.
10. Transposable Elements
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Mobile DNA sequences that can insert and excise themselves within the genome.
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Types:
- Class I (retrotransposons): Transcribe RNA before inserting a copy into the DNA genome.
- Class II (DNA transposons): Directly insert itself into the DNA genome without an RNA intermediary.
11. Biotechnology and Genetic Engineering
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Applications of genetic engineering and recombinant DNA technology.
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Techniques:
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Gel electrophoresis: Separates nucleic acids or protein fragments by size.
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Recombinant DNA technology: Combines DNA from different organism, creating recombinant molecules
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Gene cloning: Isolates and amplifies specific genes for study or application.
12. Human Genetics
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Study of genes and inheritance in human.
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Key topics:
- Mendelian inheritance: Inheritance of traits following Mendelian principles.
- Linkage analysis: Studying how genes located close together on a chromosome are inherited together.
- Genetic counseling: Providing information and support to individuals and families affected by genetic disorders.
13. Evolution at the Molecular Level
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Use molecular data to understand evolutionary relationships and processes.
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Techniques: Comparative genomics: Compares the DNA sequences of different species.
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Molecular clocks: Utilizes the rate of mutation accumulation in DNA to estimate the divergence time between species.
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Analysis of genetic variation: Studies the genetic variation within populations.
14. Phylogenetics
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Study of evolutionary relationships among species.
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Key concepts:
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Construction of phylogenetic trees based on molecular data
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Analysis of branching patterns and divergence times
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Inferring evolutionary history and common ancestor.
References:
- NCERT Biology Class 11: Chapter 6 - Molecular Basis of Inheritance
- NCERT Biology Class 11: Chapter 12 - Biotechnology: Principles and Processes
- NCERT Biology Class 11: Chapter 9 - Strategies for Enhancement in Food Production
- NCERT Biology Class 12: Chapter 3 – Molecular Basis of Inheritance
- NCERT Biology Class 12: Chapter 10 – Microbes in Human Welfare
- NCERT Biology Class 12: Chapter 13 - Organisms and Populations