Lec09_04_28_04

Lec09_04_28_04 - Chapter 9 Molecular Genetic techniques and...

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Chapter 9 Molecular Genetic techniques and Genomics New proteins are defined by three tools: define the gene encoding protein; mutant the gene in cell line or organism to knock out function, produce large quantities of purified protein for biochemical studies. Two strategies (Fig 9-1): First, isolate protein from a DNA library, large collection of individual DNA sequences representing all or part of an organism’s genome. Isolated gene can then be manipulated to produce large quantities of protein for biochemical experiments and design of probes to define where and when encoded protein is expressed in organism. Second, isolate protein or its identification based on genomic sequence, then alter it and reinsert into an organism. Observe effects of altered gene on organism, can infer its function. Both strategies require that we isolate, sequence and manipulate specific regions of the gene of interest. The field of study in which DNA sequences and gene expression patterns are studied is called genomics. 9.1 Genetic analysis of mutations. Different forms or variants of a gene are referred as allele. Mutations refers to a newly formed allele such as after treatment of an experimental organism with a mutagen. Genotype of an organism is the particular set of alleles for all the genes carried by an individual. Also denotes the particular set in an organism under study. Therefore, a wild type denotes the standard genotype or highest frequency of expressed alleles for use as a reference in breeding experiments. Phenotype on the other hand, refers to all the physical attributes or traits of an individual that arise from the genotype or particular set of alleles in an organism under study. Haploid refers to single set of chromosomes, versus two copies denoted as diploid. Most higher organisms and animals contain two copies of each gene. These may be identical for an allele, that is, homozygous for a gene, or carry different alleles and be heterozygous for a gene. Recessive mutant defined as condition in which both alleles must be mutant in order to observe mutant phenotype. Whereas, dominant mutant alleles are observed in a heterozygous individuals with one mutant allele. Recessive alleles typically result from a mutation that inactivates the affected gene leading to a complete or partial loss of function. 1
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Mutations can be articially induced in experimental organisms with ethymethane sulfonate (EMS). This acts to induce point mutations in which a G-C base is converted to an A-T pair. Phenotypic alterations can also occur as a function of substitution of an amino acid (missense mutation), a premature stop codon (nonsense mutation) or change in reading frame (frameshift mutation). Mutagenesis tends to result in many more recessive mutations than dominant ones leading to decrease in protein activity. Cell division can give rise to gametes (germ cells produce sperm and egg)
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Lec09_04_28_04 - Chapter 9 Molecular Genetic techniques and...

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