BIOL 2040 Lecture Notes - Lecture 3: Point Mutation, Polyploid, Reading Frame
27 Apr 2018
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Lecture 3 - Mutation and Selection
January 16, 2018
8:45 PM
Until there is a variation to select for, there is no change.
Mutation Produces New Variation:
• In the DNA sequence of genes
o Point mutation
• In the number of genes
o Duplication (two genes on the same chromosome), polyploidy
o New genes
• In the arrangement of chromosomes
o Polyploidy, aneuploidy, inversion
o Reproductive isolation because meiosis was disrupted in heterozygotes (some daughter cells
may be missing a chromosome, etc.)
Point Mutations
• Random copying errors
o During synthesis of DNA
o One strand may pair the wrong base to another
• Random repair errors
o After DNA damage
o Sometimes repairs successfully, sometimes doesn't
Transitions and Transversion
• Size of DNA base determines the structure of the double helix
o If it's paired wrong, it would kink the double helix
• Transition: guanine is replaced by adenine, or thymine is replaced by cytosine, or vice versa
o Tends to occur more frequently than transversion
• Transversion: pyrimidine is replaced by a purine, or vice versa
o The base that gets replaced doesn't fit and bind properly in the double helix, which kinks it
Point Mutations
• One base gets switched to something else
• Whether or not the switch does something, depends on if a new amino acid was replaced
o Some amino acids have more than one base order
• Ex. both UCU and UCA code for the amino acid serine, so the point mutation did not
effect the final product, the protein
Serious Point Mutations
• 1-base insertion
o The entire reading frame after the change is different
o All amino acids after the shift is most likely to be different
• 1-base deletion
o The entire reading frame after the change is different
o All amino acids after the shift is most likely to be different
• Mutation to a stop codon
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Until there is a variation to select for, there is no change. In the dna sequence of genes: point mutation. In the number of genes: duplication (two genes on the same chromosome), polyploidy, new genes. In the arrangement of chromosomes: polyploidy, aneuploidy, inversion, reproductive isolation because meiosis was disrupted in heterozygotes (some daughter cells may be missing a chromosome, etc. ) Point mutations: random copying errors, during synthesis of dna, one strand may pair the wrong base to another, random repair errors, after dna damage, sometimes repairs successfully, sometimes doesn"t. Size of dna base determines the structure of the double helix. Point mutation rates: 0. 1-1 mutations per genome, per replication. Mutation rate per genome, per generation for homosapiens: 1. 6, where the generation time is 20 years. Chromosomal re-arrangement: polyploidy and aneuploidy: change in chromosome number, polyploidy: complete doubling all chromosomes, aneuploidy: fission, fusion, or doubling of only some chromosomes, prevents mating with ancestors.
