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Lecture 3

HMB265H1 Lecture Notes - Genotype, Amylose, Intron
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by OneClass1348684 , Fall 2017
3 Pages
28 Views
Fall 2017

Department
Human Biology
Course Code
HMB265H1
Professor
Maria Papaconstantinou
Lecture
3

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Lecture 3: Molecular Basis of Genetic Polymorphisms & Their Detection
Mutations are the source of allelic variation
Mutation is the process whereby genes change from one allelic form to another. The creation of entirely new
alleles can occur
o Creates variation
Genes mutate randomly, at any time and in any cell of an organism
Can arise spontaneously during normal replication, or can be induced by a mutagen
Only mutations in germ line cells can be transmitted to progeny. Somatic mutations can not be transmitted
Inherited mutations appear as alleles in populations of individuals
Allele frequency is the percentage of the total number of gene copies represented by one allele
o Wild-type: allele whose frequency is ≥ 1%
o Mutant allele: allele whose frequency is < 1%
o Monomorphic: gene with only one wild-type allele
o Polymorphic: gene with more than one wild-type allele
Detectable change (difference) in a given locus/gene
Forward mutation: changes wild-type allele to a different allele
Reverse mutation: causes novel mutation to revert back to wild-type (reversion)
Mutations affecting phenotype occur very rarely
Different genes mutate at different rates
o Mutation rate varies from 1 in 1000 to 1 in 1,000,000,000 per gamete per generation
Rate of forward mutation is almost always higher than rate of reverse mutation
Mutation can occur during normal DNA replication
Mutation rate can increase after exposure to mutagen
o UV light, chemicals
Classification of Mutations
Wild type: is the starting sequence
Substitution: base is replaced by one of the other three bases
Deletion: block of one or more DNA pairs is lost
Insertion: block of one or more DNA pairs is added
Inversion: rotation of piece of DNA
Reciprocal translocation: parts of nonhomologous chromosomes change places
Chromosomal rearrangements: affect many genes at one time
SNP’s are single nucleotide polymorphisms
o They are alleles where only a single base is changed
Gene Expression and Alleles
Allelic differences at the DNA level can influence mRNA expression and/or protein function, and thus the
phenotype
Important domain of an enzyme is the active site
o If there is a mutation in the mRNA code than a different protein could be made and result in a disease due
to the non-functional protein
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Description
Lecture 3: Molecular Basis of Genetic Polymorphisms Their Detection Mutations are the source of allelic variation Mutation is the process whereby genes change from one allelic form to another. The creation of entirely new alleles can occur o Creates variation Genes mutate randomly, at any time and in any cell of an organism Can arise spontaneously during normal replication, or can be induced by a mutagen Only mutations in germ line cells can be transmitted to progeny. Somatic mutations can not be transmitted Inherited mutations appear as alleles in populations of individuals Allele frequency is the percentage of the total number of gene copies represented by one allele o Wildtype: allele whose frequency is 1 o Mutant allele: allele whose frequency is < 1 o Monomorphic: gene with only one wildtype allele o Polymorphic: gene with more than one wildtype allele Detectable change (difference) in a given locusgene Forward mutation: changes wildtype allele to a different allele Reverse mutation: causes novel mutation to revert back to wildtype (reversion) Mutations affecting phenotype occur very rarely Different genes mutate at different rates o Mutation rate varies from 1 in 1000 to 1 in 1,000,000,000 per gamete per generation Rate of forward mutation is almost always higher than rate of reverse mutation Mutation can occur during normal DNA replication Mutation rate can increase after exposure to mutagen o UV light, chemicals Classification of Mutations Wild type: is the starting sequence Substitution: base is replaced by one of the other three bases Deletion: block of one or more DNA pairs is lost Insertion: block of one or more DNA pairs is added Inversion: rotation of piece of DNA Reciprocal translocation: parts of nonhomologous chromosomes change places Chromosomal rearrangements: affect many genes at one time SNPs are single nucleotide polymorphisms o They are alleles where only a single base is changed Gene Expression and Alleles Allelic differences at the DNA level can influence mRNA expression andor protein function, and thus the phenotype Important domain of an enzyme is the active site o If there is a mutation in the mRNA code than a different protein could be made and result in a disease due to the nonfunctional protein
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