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CSU BZ 220 - Mutations

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BZ220 1st Edition Lecture 5Outline of Previous LectureI. Which tissues carry genetic infoA. Pangenesis TheoryB. Germ Plasm TheoryII. How is genetic info passed onA. Blending inheritanceIII. Modern Gene VocabularyIV. Gregor MendelA. Main experimentsB. Principle of DominanceC. Principle of SegregationD. Principle of Independent AssortmentE. Significance of Mendel’s discoveries for evolutionV. Hugo De VriesA. Mutation TheoryB. Discrete Vs. Continuous VariationC. Mendelians vs. Biometricians VI. Continuous VariationA. Environmental EffectsB. Co-Dominant AllelesC. Multiple GenesD. Epistasis E. Explanations of Continuous VariationVII. Modern Synthesis Outline of Current LectureI. Structure of DNA and genetic codeII. Causes of MutationsIII. Types of MutationsA. Nucleotide mutationsB. Chromosomal mutationsIV. Effects of mutationsCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Nucleotides are composed up of a phosphate group, a 5-carbon sugar, and a nitrogenousbase. There are four nitrogenous bases: adenine, guanine, cytosine, and thymine. These nucleotides are what make up DNA. DNA is a double helix of genetic information and was proposed in 1963 by Watson and Crick. The flow of genetic information is DNA to mRNA to Amino Acid to Protein. The DNA is composed up of nucleotides that can be transcribed into mRNA and then translated into amino acid chains that create proteins. Translation is a very specific yet redundant process. Each codon (a set of 3 nucleotides) only codes for one particular amino acid; however, more than one codon can code for the same amino acid. For example, the amino acid Proline can be coded by the codon CCC or CCU but CCU can never code for Leucine or any other amino acid besides Proline.When DNA is synthesized, the double helix must first unwind and then the nucleotides of each helix must be matched up with another nucleotide. If the wrong pairing of a nucleotide occurs, a mutation could result, but most of these kinds of mistakes are repaired by specific enzymes watching over the process of DNA synthesis. Mutation caused by these types of DNA replication mistakes may not occur very often; however, these are the most common sources of mutations that get passed on to the next generation. Another cause of mutation is environmental agents. Environmental agents include UV, nuclear radiation, and organic solvents often found in tobacco products. These environmental agents have the ability to break DNA strands and change the structure of a nucleotide so that it is copied incorrectly. For example the organic solvent benzopyrene in tobacco can be inserted into a DNA strand causing an extra nucleotide to be inserted opposite of it. Environmental agent caused mutations are not passed on to offspring unless the mutation directly effects the gonads. There are two types of mutations: nucleotide and chromosome mutations. Nucleotide mutations can occur through substitution, insertion, or deletion. Nucleotide substitutions are called point mutations. These point mutations can further be divided into transitions and transversions. Transitions are more common and involve one purine nucleotide (adenine and guanine) to be swapped for the other purine or one pyrimidine (cytosine and thiamine) being swapped for the other pyrimidine. These are thought to be more common because it is likely that the repairing enzymes cannot as easily pick up on this slight change as well as the large change from a purine to a pyrimidine found in transversions. Nucleotide substitutions (point mutations) can be synonymous or nonsynonymous due to the redundancy in genetic information discussed above. Synonymous mutations are those that are considered silent and will not cause a change in the amino acid while nonsynonymous will cause an amino acidchange or cause a mis-sense mutation where the original amino acid is changed into a stop codon. Nucleotide insertions and deletions are known as frame-shift mutations because more than one amino acid is affected. In a nucleotide insertion just as the name suggests an extra nucleotide is inserted into the genetic code which causes all of the amino acids after the mutation to be shifted upwards one in the genetic code. A deletion also known as a non-sense mutation is when a nucleotide that was supposed to be present is missing resulting in a downwards shift of all amino acids after the mutation. In addition to nucleotide mutations, there are also chromosome mutations. The four types of chromosome mutations are deletion, duplication, inversion, and reciprocal translocation. Deletion is the removal of an entire section of a chromosome or the removal of multiple genes. A duplication forms a redundancy in the genetic code and an amino acid is coded for twice instead of once. An inversion is when a codon’s order of nucleotides is flipped ina chromosome (instead of ABC you have CBA). A reciprocal translocation is when two codons are swap a nucleotide in the chromosome (have CDE and NOP now becomes CON and EDP where the P and C in the codons were swapped). The duplication and deletions of sections of chromosomes promotes unequal crossing over which can cause gene duplication and multigene families. Gene duplication is the source ofnew genes while multigene families causes multiple copies of genes that are very similar. Chromosome inversion can often have little effect if none of the genetic material is lost and no genes are disrupted. If genetic material is lost or genes are disrupted, recombination is suppressed due to the chromosome’s inability to cross over. On occasion these mutations can become extremely common in certain populations, but the reason as to why is still unknown. Chromosome translocation results in an odd number of chromosomes and can decrease fertility, for some sperm or egg cells may not get any chromosomes while another may get morechromosomes than necessary. A common chromosomal division error in humans can be seen in the trisomy of chromosome 21. This trisomy where an egg cell gets 3 sets of chromosomes instead of 2 is the main cause of Down syndrome. This chromosomal division error increases in probability as the woman ages. Chromosome polyploidy is also a mutation of the chromosome but if usually found in plants and not animals. In this mutation and entire sets of chromosomes are duplicated and mutants become


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