Lecture_7_-_Gene_Functions_and_Gene_Mutations

Lecture_7_-_Gene_Functions_and_Gene_Mutations - Lecture 7...

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Lecture 7 Lecture 7 Modifications of Modifications of Mendelian Ratios Mendelian Ratios Gene Function & Mutations
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Testing for Allelic Mutations Testing for Allelic Mutations A mutant allele can be created when the nucleotide sequence in the DNA that constitutes the allele is changed –a process called mutation Mutations always involve a change in the physical composition of an allele However, mutations do not always produce phenotypic changes
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Testing for Allelic Mutations Testing for Allelic Mutations Mutations that produce dominant alleles almost always produce phenotypic changes Individuals that inherit either one (heterozygotes) or 2 (homozygotes) of the dominant allele will exhibit the dominant phenotype However, mutations that produce recessive alleles may or may not produce phenotypic changes Only individuals that inherit 2 copies of the mutant allele (homozygotes) will exhibit the recessive phenotype
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Variation among Allelic Effects Variation among Allelic Effects The term population refers to all or part of the members of a species A specie population can contain many different mutant alleles for a given gene Each of these different alleles can have different phenotypic effects on individuals in the population In nature, mutations provide the raw material for evolution to occur
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Variation among Allelic Effects Variation among Allelic Effects Mutations that effect the morphology of the individual are called visible mutations Mutations that impair or inhibit reproduction are called sterile mutations If a sterile mutation is dominant and completely inhibits reproduction, it will not survive in a population Mutations that interfere with necessary body functions are called lethal mutations Lethal mutations cause death in an individual Many genes are capable of mutating to lethals
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Variation among Allelic Effects Variation among Allelic Effects Dominant lethal alleles that act early in life only last one generation in a population Dominant lethal alleles that act later in life, after reproduction, can be passed on to the next generation Recessive lethal alleles can last many generations in a population, sometimes forever, because they can be masked by wild-type alleles
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Genes Produce Polypeptides Genes Produce Polypeptides Organisms contain many, many different genes and most of these genes exist in many different allelic forms This explains how genes produce extensive genetic and phenotypic variation for specific traits However, it does not explain how genes function to affect phenotypes The discovery that genes produce polypeptides explains how genes affect phenotype
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This note was uploaded on 05/07/2011 for the course DARY 2072 taught by Professor Hay during the Spring '09 term at LSU.

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Lecture_7_-_Gene_Functions_and_Gene_Mutations - Lecture 7...

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