biology-class-12-unit-06-chapter-11-genetics-and-evolution-molecular-basis-of-inheritance-l-11-12-jnbxumuh3ze

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<h3 id="successpoint-mutationsuccess"><Success>Point mutation</Success></h3>
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<p><strong>Base pair substitution</strong></p>
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<p>Change from one base pair to another</p>
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<p>Transition mytation: purine replaced by purine and pyrimidine replaced by pyrimidine</p>
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<p>Transversion mutation: Purine replaced by pyrimidine and pyrimidine replaced by purine</p>
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<h3 id="successpoint-mutationsuccess-1"><Success>Point mutation</Success></h3>
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<p>Some examples of point mutation</p>
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<p>Missense mutation -  a gene mutation in which a base pair changes in an mrna codon so that different amino acid is inserted into polypeptide chain</p>
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<h3 id="successnonsense-mutationsuccess"><Success>Nonsense mutation</Success></h3>
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<li>A gene mutation in which a base pair change alters an mRNA codon for an amino acid to a stop codon (UAG, UGA, UAA)</li>
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<h3 id="successneutral-mutationsuccess"><Success>Neutral mutation</Success></h3>
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<li>A gene mutation in which a base pair change a codon in the mRNA such that the resulting amino acid substitution produces no detectable change in the function of protein translated from that mRNA</li>
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<h3 id="successsilent-mutationsuccess"><Success>Silent mutation</Success></h3>
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<ul>
<li>A gene mutation that changes a base pair but the altered codon in the mRNA specifies the same amino acid in the protein</li>
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<h3 id="successframeshift-mutationsuccess"><Success>Frameshift mutation</Success></h3>
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<li>If one or more base pairs are added or deleted from a protein coding gene, the reading frame of a mRNA can change downstream of the mutation</li>
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<h3 id="successbase-anologssuccess"><Success>Base anologs</Success></h3>
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<p>Bases that are similar to those normally found in DNA</p>
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<p>Example: 5-bromouracil base analog of thymine</p>
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<h3 id="successvariation-in-chromosomal-numbersuccess"><Success>Variation in chromosomal number</Success></h3>
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<p>When an organism or a cell has one complete set of chromosomes or an exact multiple of complete sets, that organism or cell is said to be euploid</p>
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<p>Chromosome mutations that result in variations in the number of chromosome sets occur in nature, and the resulting organism or cells are also euploid. Chromosome mutations resulting in variations in the number of individual chromosomes are examples of aneuploidy</p>
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<h3 id="successtypes-of-aneuploidysuccess"><Success>Types of Aneuploidy</Success></h3>
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<p>Nullisomy (a nullisomic cell) involves a loss of one homologous chromosome pair i.e. 2N-2</p>
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<p>Monosomy (a monosomic cell) involves a loss of a single chromosome i.e. 2N-1</p>
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<p>Trisomy (a trisomic cell) involves a single extra chromosome i.e. 2N+1</p>
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<p>Tetrasomy (a tetrasomic cell) involves an extra chromosome Pair i.e. 2N+2</p>
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<h3 id="successchanges-in-complete-sets-of-chromosomessuccess"><Success>Changes in complete sets of chromosomes</Success></h3>
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<p>Monoploidy. A monoploid individual has only one set of chromosomes instead of the usual two sets</p>
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<p>Polyploidy. Polyploidy is the chromosomal constitution of a cell or an organism that has more than the normal two sets of homologous chromosomes</p>
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<h3 id="successdirect-repair-systemsuccess"><Success>Direct repair system</Success></h3>
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<p>Mismatch repair by DNA polymerase proofreading</p>
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<p>Repair of UV-Induced pyrimidine dimers by photolyase enzyme, coded by phr gene</p>
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<p>Repair of alkylation damage by 06- methylguanine methyltransferase enzyme encoded by ada gene</p>
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<h3 id="successexcision-repair-systemsuccess"><Success>Excision repair system</Success></h3>
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<p>Base excision repair - depurination and deamination mutations are repair by glycosylase enzyme</p>
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<p>Nucleotide excision repair - By UvrA, UvrB, UvrC and UvrD enzymes encoded by uvrA, uvrB,uvrC and uvrD genes respectivel</p>
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<p>Methyl directed mismatch repair - By MutL, Muts & MutH enzymes encoded by mutL,muts & mutH genes respectively</p>
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<h3 id="successanswer-these-questionssuccess"><Success>Answer these Questions</Success></h3>
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<p><strong>Question 1.</strong> What is Mutation?</p>
<p><strong>Question 2.</strong> What will be the effect of mutation on living system?</p>
<p><strong>Question 3.</strong> What is Trisomy?</p>
<p><strong>Question 4.</strong> Define Mutagen</p>
<p><strong>Question 5.</strong> Do you think mutation can be repaired?</p>
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