bio 207 lecture 7.docx

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University of Alberta
Biology (Biological Sciences)
Lesley Harrington

BIOL207 B01 Lec07 2014-01-20 CHAPTER 4 A. Definitions 1. Mutation = change i. Change in DNAsequence and/or phenotype … ii. Not all mutations results in mutant phenotypes iii. Not all mutations are deleterious 1. can be neutral 2. can give a selective advantage 3. can be deleterious (can be selective disadvantage) iv. Most mutations that affect a protein coding gene or its expression are loss-of- function mutations v. Most mutations tend to be silent or bad; not likely to provide a new function/ better function 2. All variation in DNAcomes from mutation i. Polymorphism (rather than mutation) describes variants that are common in a population (>1%), and for which no obvious “wild-type” allele can be distinguished ii. Variation in phenotype and DNAsequence; we don’t know which variation is the actual phenotype or which is a mutant B. Origins of mutations 1. spontaneous OR induced (purposeful or not); induced is usually in an experimental context; 2. biological, chemical, physical mutagens; i. mutations of biological origin 1. DNAstrand slippage; Within the category of biological mutations, any mutation that occurs during DNAsynthesis is a biological mutation. It will be spontaneous; C’s from other parts of the strand will pair with G’s out of line, mispairing is a consequence; a. Tandem repeats of simple sequences (di-, tri-, tetra- nucleotides) are prone to mistakes (i.e. slippage) during replication b. This can cause increase or decrease in the number of repeats present at a given locus c. Decrease  two nucleotides are skipped and are looped out of the strand; d. Increase  Extra nucleotides join onto the new strand and you have an extra pair of repeats e. Depends if repeats are skipped/ added on the daughter strand or the template strand f. Slippage occurs frequently enough to produce polymorphisms that can distinguish individuals in a population, but is usually heritable between generations; common in the population but is rare enough to remain harmless; not because slippage occurred in your parents/ their parents, but likely in your great-great grandpa and not their great-great grandpa; g. Usually occurs in non-coding DNA; mainly useful in forensic DNAand finger printing h. Most of the genome does not code for genes, so it wont affect your phenotype/ fitness until you try and detect that phenotype; i. SSR = simple sequence repeat = microsatellite loci 2. Transposable elements Barbara McClintock Patches of purple when some genes jump out and into different genes and can disrupt genes. a. Two main classes i. Class I : move by copy/paste of an RNA intermediate; involves the evolution of retroviruses; can copy themselves throughout the gene; ii. Much more common because they have double the DNAamount iii. Class II: move by cut and paste of the original DNA
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