Textbook Notes (363,147)
Canada (158,221)
Biology (653)
BIO207H5 (42)

Ch 7.docx

15 Pages
Unlock Document

University of Toronto Mississauga
Karen Williams

Ch. 7: DNA Mutation, DNA repair, and Transposable Elements -DNA can be changed in a number of ways, including through spontaneous changes, errors in the replication process, or the action of radiation or particular chemicals -Chromosomal mutations: changes involving whole chromosomes or sections -point mutation: a change of one or a few base pairs (another broad type of change in the genetic material). A point mutation may change the phenotype of the organism if it occurs within the coding region of a gene or in the sequences regulating the gene -point mutations that have been of particular interests to geneticists are gene mutations -gene mutations: mutations which affect the function of genes. -a gene mutation can alter the phenotype by changing the function of a protein -Transposable elements: undergo transposition (change in position). Genetic change also occur when certain genetic elements in the chromosomes or prokaryotes and eukaryotes move from one location to another in the genome -note that not all mutations lead to altered proteins and that not all mutations are in protein encoding regions DNA Mutation Adaptation versus Mutation th -early in the 20 century, there were two opposing schools of thought concerning the variation in heritable traits 1.Mutation theory: variation among organisms resulted from random mutations that sometimes happened to be adaptive 2.Adaptation theory: others thought the variations resulted from adaptation (that is the environment induced an adaptive inheritable change) -Luria and Delbruck experiment, if mutation theory is correct, there should be a fluctuation in the number of T1-resistant cells in generation 4 (T1 phage cells added to WT E. coli in generation 4) because the mutation to T1-resistance occurred randomly in the population and did not require the presence of T1 -for adaptation theory to be correct, a certain proportion of the generation 4 cells will be induced at that time to become resistant to T1. Most importantly, that proportion will be the same for all identical cultures because adaptation would not commence until T1 was added -Luria and Delbruck observed a large fluctuation in the number of resistant colonies among identical cultures. Thus supporting the mutation theory Mutations Defined -Mutation is the process by which the sequence of base pairs in a DNA molecule is altered. A mutation may result in a change to either a DNA base pair or a chromosome -if a mutation happens to occur in a somatic cell (in multicellular organisms), it is a somatic mutation. -the mutant characteristic affects only the individual in which the mutation occurs and is not passed on to the succeeding generation -in contrast, a mutation in the germ line of sexually reproducing organisms, germ-line mutation, may be transmitted by the gametes to the next generation, producing an individual with the mutation in both its somatic and germ-line cells -two terms are used to give a quantitative measure of the occurrence of mutations 1. mutation rate: the probability of a particular kind of mutation as a function of time, such as the number of mutations per nucleotide pair per generation, or the number per gene per generation 2. mutation frequency: the number of occurences in a particular kind of mutation, expressed as the proportion of cells or individuals in a population, such as the number of mutation per 100,000 organisms or the number per 1 million gametes WHATS THE DIFFRENCE BETWEEN THEM?!??! Types of Point Mutations -2 general categories: -base pair substitutions -base pair insertions or deletions -base-pair substitution mutation: a change from one base pair to another in DNA. 2 general types -transition mutation: a mutation from one purine-pyrimidine base pair to the other purine- pyrimidine base pair (ex. A-T to G-C). This means that the purine one strand of the DNA (A in the example) is changed to the other purine, while the pyrimidine on the complementary strand (T, the base paired to the A) is changed to the other pyrimidine. -transversion mutation: a mutation from the purine- pyrimidine base pair to a pyrimidine - purine base pair (ex. G-C to C-G, or A-T to C-G). This means that the purine on strand of the DNA (A in the second example) is changed to a pyrimidine (C in the example), and again the complementary strand changes to match - REMEMBER A and G ARE PURINES, AND C and T ARE PYRIMIDINE -base-pair substitutions in protein coding genes also are defined according to their effects on amino acid sequences in proteins. -change can be insignificant or noticeable -missense mutation: a gene mutation in which a base-pair change causes a change in an mRNA codon so that a different amino acid is inserted into the polypeptide. Phenotypic change may or may not result. IF it doesnt change it has a special name. -example changing: A-T, A-T, A-T to G-C, A-T, A-T (lysine *5- AAA -3+ to glutamic acid *5-GAA- 3+) -nonsense mutation: a gene mutation in which a base-pair change alters an mRNA codon for an amino acid to a stop (nonsense) codon. A nonsense mutation cuases premature termination of polypeptide chain synthesis, so shorter than normal polypeptide fragments (often non functional) are released from the ribosome -neutral mutation: a base pair change in a gene that changes a codon in the mRNA such that the resulting amaino acid substitution produces no detectable change in the function of the protein translated from that message. A neutral mutation is a subset of missense mutation. Phenotype does not change. -lysine gets changed to arginine but they both have similar properties that the proteins function may not alter significantly -silent mutation: also known as synonymous mutation. A mutation that changes a base pair in a gene, but the altered codon in the mRNA specifies the SAME amino acid in the protein. In this case, the protein obviously has a wild type function. Silent mutations most often occur by changes such as this at the third (wobble) positions of a codon -Frameshift Mutation: if one or more base pairs are added to or deleted from a protein-coding gene, the reading frame of an mRNA can change downstream of the mutation. Usually results in a non- functional protein. -was instrumental in scientists determining that the genetic code is atriplet code
More Less

Related notes for BIO207H5

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.