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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
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