Chapter 6: Molecular Basis of Inheritance

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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-24"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Sol.</strong> Sickle-cell anaemia is an autosome linked recessive trait.</p>
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<li>In this genetic disorder point mutation in $\beta$-globin chain results in change of glutamate (glutamic acid) to valine at sixth position.</li>
<li>Only the homozygous individuals for $\mathrm{Hb}^{\mathrm{s}}$ 2, i.e., $\mathrm{Hb}^{\mathrm{s}} \mathrm{Hb}^{\mathrm{s}}$ show the diseased phenotype.</li>
<li>The heterozygous individuals $\left(\mathrm{Hb}^{S} / \mathrm{Hb}^{A}\right)$ are carriers.</li>
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<p><Success>Sol. to be continued</Success></p>
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<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-29"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Sol.</strong> Polypeptide synthesis is signalled by two initiation codons commonly AUG or methionine codon and rarely GUG or valine codon.</p>
<ul>
<li>
<p>Since there are 64 triplet codons and only 20 amino acids, the incorporation of some amino acids must be influenced by more than one codon.</p>
</li>
<li>
<p>Only tryptophan (UGG) and methionine (AUG) are specified by single codons.</p>
</li>
<li>
<p>AUG codes for methionine in both prokaryotes and eukaryotes.</p>
</li>
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<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-32"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Sol.</strong> RNA was the first genetic material.</p>
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<li>
<p>There is now enough evidence to suggest that essential life processes (such as metabolism, translation, splicing, etc.), evolved around RNA.</p>
</li>
<li>
<p>RNA used to act as a genetic material as well as a catalyst (there are some important biochemical reactions in living systems that are catalysed by RNA catalysts and not by protein enzymes).</p>
</li>
<li>
<p>But, RNA being a catalyst was reactive and hence unstable.</p>
</li>
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<p><Success>Sol. to be continued</Success></p>
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<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
</div>
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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-36"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Sol.</strong> In eukaryotes, the monocistronic structural genes have interrupted coding sequences i.e., the genes in eukaryotes are split.</p>
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<li>
<p>The coding sequences or expressed sequences are defined as exons.</p>
</li>
<li>
<p>These sequences (exons) appear in mature or processed RNA.</p>
</li>
<li>
<p>The exons are interrupted by introns or intervening sequences which do not appear in mature or processed RNA.</p>
</li>
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<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
</div>
</font>

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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-43"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<ul>
<li>
<p><strong>Erwin Chargaff</strong> observed that for a double-stranded DNA, the ratios between adenine and thymine and guanine and cytosine are constant and equals one.</p>
</li>
<li>
<p>On the other bond <strong>Matthew Meselson</strong> and <strong>Franklin Stahl</strong> in 1958 performed experiments on E.coli to prove that DNA replication is semi-conservative.</p>
</li>
<li>
<p>But had no contribution it the development of double helix model.</p>
</li>
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<div style='text-align : center'>
<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
</div>
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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-44"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Ques.</strong> DNA is a polymer of nucleotides which are linked to each other by $3^{\prime}-5^{\prime}$ phosphodiester bond.</p>
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<li>To prevent polymerisation of nucleotides, which of the following modifications would you choose?</li>
</ul>
<p class="fragment">(a) Replace purine with pyrimindines <br>
(b) Remove/Replace 3' $\mathrm{OH}$ group in deoxy ribose <br>
(c) Remove/Replace 2' $\mathrm{OH}$ group with some other group in deoxy ribose <br>
(d) Both (b) and (c) </p>
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<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
</div>
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<Success><font size="5"><b>Molecular Basis of Inheritance</b></font></Success>
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<h4 id="primarymultiple-choice-questions-mcqsprimary-46"><Primary>Multiple Choice Questions (MCQs)</Primary></h4>
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<p><strong>Sol.</strong> The enzyme called DNA polymerase progressively adds deoxyribonucleotides to the free $3^{\prime}$-end of the growing polynucleotide chain so, that replication of the $3^{\prime}-5^{\prime}$ strand of the DNA molecule is continuous (growth of the new strand in $5^{\prime} \rightarrow 3^{\prime}$ direction).</p>
<ul>
<li>So, to prevent polymerisation of nucleotides $3^{\prime} \mathrm{OH}$ group in deoxyribose should be replaced/removed.</li>
</ul>
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<hr>
<font size ="4">
<div style='text-align : center'>
<span style="color:blue">Multiple choice questions (MCQs)</span> $\rightarrow$ Very short answer type questions $\rightarrow$ Short answer type questions $\rightarrow$ Long answer type questions
</div>
</font>