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Quiz

BIOL239 Study Guide - Quiz Guide: Wild Type, Pyrimidine, PurinePremium

7 pages81 viewsWinter 2017

Department
Biology
Course Code
BIOL239
Professor
Christine Dupont
Study Guide
Quiz

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Mutations
What are mutations
oHeritable changes in base sequences that modify the information content of DNA
used to identify mutations, we first need to identify what the 'normal' or 'wildtype'
allele is Heritable from cell to cell not just parent to child
What is a wild type allele?
oThere is still some disagreement as to how this is defined
oGenerally, it is the allele(s) that dominates in a wild population
oOthers consider any allele present in more than 1% of the population to be a
wildtype allele
oWildtype alleles can be recessive or dominant
oDominant and recessive are really a reflection of what goes on at the molecular
level. A dominant allele usually masks the presence (effect) of the recessive
allele.
oMore than one wildtype allele can exist for a gene = polymorphic gene
e.g., seed coat colour in Indian corn
What are the different kinds of mutations?
oa) Substitution:
o1. Transition: Purine for Purine; Pyrimidine for Pyrimidine
o2. Transversion: Purine for
Pyrimidine; Pyrimidine for Purine
b) Deletion
c) Insertion
d) Inversion - Upside-down
and backwards, may or may
not impact the phenotype
e) Reciprocal translocation - Part of one chromosome has been replaced
with a region from another chromosome and vice versa -changing places
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How frequent are
mutations?
oIn
general,
mutation
rates fall
into the
range of
2-12 x 10-6
mutations per gene, per generation
oCan vary between <10-8 to >10-4 depending on the gene and species
How would you estimate rates of mutations of a particular gene?
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oInbreed homozygous recessive for a trait --> produce lots of offspring to see
change in phenotype
oOf course, many mutations occur that do not affect phenotype (most mutations are
not in genes)
oThe only way to detect these is through molecular methods e.g. DNA sequencing
Issue with evolution?
oEvolution is the change in the inherited characteristics of populations over
generations
oBut what is the mechanism? Is the selective pressure causing the adaption? Or
was it already there and just uncovered?
Describe the Luria-Delbruck 'Jackpot' or Fluctuation hypotheses̈
oSet up small vials of bacterial culture and let them grow for a specified amount of
time, to let whatever mutations there continue then at the end add equal portions
of each culture to plates containing media along with phage that
kills them
oobserved the results The
virus is the selective
pressure
oQuestions: How/why do the
resistant colonies appear
oHypothesis #1: Adaption is
a physiological response to
phage pressure - Should see low
numbers in colonies but
found in all Believes that
resistance is the result of
active adaptation to the
selective pressure (phage)
obased on Lamarck's theory of evolution by
acquired traits
oThe selective pressure causes/drives the mutation
oe.g., if you develop large muscles as a result of delivering refrigerators for a
living, then your offspring will also have large muscles
oIf so, then all plated cultures should adapt similarly, resulting in similar numbers
of resistant colonies Black colonies have a resistant mutation for phage resistance
oHypothesis #2 Resistance is a result of random mutations, << Proved right
oExclusive of the selective pressure
Based on Darwin's theory of evolution of natural variation and selection
If so, then there will be differences in the numbers of resistant colonies
obtained due to random mutation
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Conclusions from Luria-Delbruck 'Jackpot' or Fluctuation tesẗ
oResistance occurs as a result of random, spontaneous mutations that happen at
various time points before exposure to the selective agent (selective pressure is
not causing the mutation)
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