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Gene Mutations

gene mutations

mutation -an inherited change in genetic information(inherited alteration in DNA sequence) -thedescendants may be cells or organisms
Main Catagories of Mutations - Somatic Mutation -Germ-line Mutation
Somatic Mutation -arise in somatic tissues, non-reproductive cells -passed to new cells through mitosis, creating a clone of mutant gene (mosiacism) -the earlier in development the mutation occur, the greater the number of clone - no obvious phenotype effect -cancer
Germ-line Mutation - occur in cells that give rise to gametes - mutation passed on via meiosis and sexual reproduction to approximately 1/2 of the next generation - who will carry the mutation in all (somatic & germ-line) their cells
Types of Gene Mutations - Base Substitution Transversion & Transition - Insertion & Deletions - Expanding nucleotide repeats
Base Substitutions simplest, change in single nucleotide in DNA - Transition: pu/py to pu/py (PU = A&G | PY=C&T) More frequent - Transversion: pu/py to py/pu
Insertion & Deletions the most frequent lead to frameshift mutations - alter aas encoded by the nucleotides - affect phenotype
Expanding nucleotide repeats mut increase in copy of a set of nucleotides(CN(any)G) - number of copies of the nucleotide repeat correlates with severity or age of onset of the disease -more repeats = more repeats --Anticipation, more severe in each generation
Huntington disease Fragile-X syndrome - nuc. expands within the coding part of a gene, producing a toxic protein that has an extra glutamine residues (the aa encoded by CAG) - or outside the coding region of gene, affect its expression, cause DNA to be methylated, turn off transcription.
Nucleotide Repeat Mechanism - expansion occurs in DNA replication - related to the formation of hairpins and other DNA structures that form in ss DNA w/ of nuc repeats. -structures may interfere with norm rep by via strand slippage,misalignment, or stalling of replication
Phenotypic Effects of Mutations - missense mutation - nonsense mutation - silent mutation - neutral mutation - Loss-of-function mutations - gain-of-function mutation - conditional mutations - lethal mutations
missense mutation (prot encoded) - base substitution that results in a different amino acid in the protein
nonsense mutation (prot encoded) - changes a sense codon (one that specifies an amino acid) into a nonsense codon (one that terminates translation) - if it occurs early in the mRNA sequence, the protein will be greatly shortened and will usually be nonfunctiona
silent mutation (prot encoded) - changes a codon to a synonymous codon that specifies the same aa (DNA still altered) - some do have phenotypic effects in use of diff isoaccepting tRNAs: affect rate of prot synth & folding, or alter seqs near exon-intron junctions & affect splicing
neutral mutation (prot activity) - a missense mutation that alters the amino acid sequence of the protein but does not change its function - occur when one aa is replaced by another thats chemically similar/ same charge ex. genes that encode for hemoglobin: still transport oxygen
Loss-of-function mutations (prot activity) - complete or partial absence of norm prot funct, alters prot structure - cant work corrrectly or mut occur in reg'ory regions that affect transcrip, translat, or splicing of the prot - recessive, cystic fib reg prot that regs Cl ion in and out of cell
gain-of-function mutation (prot activity) - produce entirely new trait or cause a trait to appear in an inappropriate tissue or time in development, dominant - mut in gene encoding for growth factor receptor to stimulate growth - continute to do so without a gfactor
conditional mutations lethal mutations - under certain conditions - premature death
Mutation rate - frequency with which a particular mutation arises in a population -influenced by both genetic and environmental factors
Rate of mutation -probability of any one base changing ~2 x 10-8 per base pair per generation
Mutation frequency -incidence of loss of function mutation in a specific gene ~ 10-5 per person in population using dominant or X-linked
Created by: Yourdanos