l1bio261f2014
TRANSCRIPT
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Molecular and General Genetics 2014 Biol261/2
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The science of genetics is relativelynew.
Modern breeding designs andmolecular capabilities have acceleratedthe pace and scope of understanding thenature of genes and characterexpression, promising a biologicalrevolution
But, the fabric of this revolution isbuilt using an ,applies various causaloperating at different levels of
(organismal andmolecular) that are at well integratedin .
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DEFINITIONSGenetics is defined as:
(1) The studyofgenes(2) The studyof inheritance. (Griffiths et al. 9e)The study ofall aspects of genes(Griffiths et al. 10e)(3)Genetics is the study ofheredity and variation(Lewontin 1974)
Genetics is studied on different natural scalesof organization: molecular, chromosomal,transmission genetics, population and evolutionary
genetics, genomics.
Consequently, for example, definitions of a gene differwith the scale and nature of the study.
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ClassicalGeneticsModel I involve genes (only) governing theexpression of a character or phenotype:genetic determination- a
set of instructions for turning undifferentiated environmentalmaterials into making a specific organism, regardless of theenvironment.
GeneticDeterminism
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Model II:Environmental determinism Expressed DNAcontains the information, but the local environment (internal orexternal)determines the actual course of development or theexpression of a character state. For example, gene expressionmay be governed by chromosomal tags or intervening sequences,sex in turtles and crocodiles is determined by eggdevelopment temperature.
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Model III:genotype - environment interaction - The courseof development, or phenotypeexpression depends on the
genes an individual inherits from its parents and thesequence of specific environments an individual encountersduring development.
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Figure 1-18
Genes and the environment both influenceeye size in Drosophila
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Our understanding of Genetics, summarized by the authors ofyour text book, pre-eminent geneticist of our generation, is.. Genescannot generate or even dictate the structure of an organism bythemselves. The environment (internal or external) has a crucial
ongoing effect and sometimes it is a controlling component ofexpression. Ch 1, Griffiths et al 9thedition.
Nonetheless: Many write, talk and act as if genes alonedetermine phenotype expression.
In some cases this appears correct, in others this may be amisleading characterization.
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Development variation unrelated to known or controlled allelic orenvironmental variation, may produce asymmetrical or highly
variable characters. Thisdevelopmental noisecauses variability
not related to specific environments or genes
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Textbooks:
An Introduction to Genetic AnalysisGriffiths et al. 10thedition - required.
Solutions Manualfor An Introduction to
Genetic Analysis -suggested
I clicker - required
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WEB Site for Molecular and General Genetics:
https://www.myconcordia.caChoose Course websites (Moodle)
Lecture slidesRecommended Problems
Course outline and grading scheme
The text book publisher, W.F. Freeman has a web sit
www.whfreeman.com
with study aids including animations.
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Mandatory tutorialsmeet once a week for 2 hr,beginning next week
A teaching assistant will reviewthe previous weeksmaterial, discussillustrative problems, and a week later,testyou and other students on the lecture material.
Each week, a section is covered in 2 lectures,say section A. The following week, problems related tosection A are solved in tutorial. Student teams of 4-5 willpresent the solution to a pivotal selected problem.
In the next week section A will be the subject of the quiz.
Your tutorial grade will be largely based on your quiz marksand yourpresentation scores.
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The readings in the text and the assignedproblems are in the dates reading andproblems EXCEL file
(Biol 261 Schedule.xls)
For example,Week 1
ReadCh: 1, 2.0-2.2, 2.4-2.6
PrintCh 2: 15, 18, 28,31,33,34,40,43,50,51,61,63,64
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Grading:
20% Tutorial
40%
2 Midterm Exams40% Final
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SECTION 1 : Classic Genetics
Mendelian Genetics 1 gene, 2 alleles
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Scientific genetics beganwith Gregor Mendelwho in
the 1850s used differentpure-breeding strains in acontrolled breedingexperiment to test their mode
of inheritance.
See C. Stern and E.R. SherwoodThe Origin of Genetics a MendelSource Book
The laws of inheritance were independentlyrediscovered in 1900 by Hugo de Vries,
Carl Correns, and Erich von Tschermak.
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Single Gene Inheritance
During Mendels university education inbotany, breeding and physics,physicists were
interested in the atomic nature of matter.
John Dalton is considered the originator ofmodern atomic theory. But Daltons atomichypothesis did not specify the size of atoms.
Therefore it was a major landmark when in1865 Johann Josef Loschmidtmeasured thesize of the molecules that make up air.
Loschmidtwas also from the Czech Republic aprofessor of Physics in Vienna inevitably part
of Mendels education.
So it was not surprising that Mendel set out to lookfor the atoms of inheritance.
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A) Experimental Control. Start with a
population, any sexual populationis
defined by the extent ofpotentially
interbreeding individuals. In Mendels
case he restricted breeding individuals
to the strains he used within his garden
plot below.
The more control you have over its
ecology, you decrease the influence
of chance effects of the environmenton inheritance and expression.
But, there are always other levels of
chance variation.
B) Statistics One of Mendels
conceptual breakthroughs in dealingwith this variation was his statistical
approach, the larger the sample size
(statistical) , and the more factors
you control (experimental), the
smaller the influence of chance
effects on the experimental
outcome.
Foundations Experimental Control and Statistics
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Inbred,pure breeding (selfed or bred withan individual from the same strain),
colored (Purple ish), Psium sativumParental line
X
X
Inbred Strain
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X
X
Second (white) pure breeding,inbred Parental line
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Alternative Hypotheses:(1)Discrete categorical inheritance or
(2) Blending continuous inheritance
Test: crossing inbred white and purple-floweredpea strains, are colors retained in hybrids,
through several generations or are they lost,changed or otherwise altered (blended) indifferent offspring generations?
Methods:(1) define the character-flower color(white, purple with no intermediates), then
(2) the breeding design.
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Controlfor differences
in the cross of pure-breeding parentalstrains
Reciprocal CrossesMale purple pollen to
white stigma (shown),and male white pollentopurple stigma (notshown).
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XParentals
(F1)
Discrete or Blending Inheritance?
Breeding design: Reciprocal Monohybrid Cross
Inbreed or self fertilize the (F1).
In the first generation: there was no blending butthere was evidence of possible character loss.
first filial generation
50% 50%
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Parental Cross
F1:observations?Interpretation
X
X
Count224 white (0.24 total)705 purple (0.76 total)
(1: 3.15)
F2:observations
Odd fact -the ratiochanged from 50/50 in the
parentals, 100% purple inthe F
1 to 3:1 in the F
2?
Interpretation
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F2
225 white, 705 purple or 3:1
Test the particle variation by inbreeding F2plants
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F2
F3
Inbreed (self)
(pp) (pP) (PP)
Dominance hides the frequency of different particles,gametes or alleles -actually 50% p /50%P
Dominance is an empirical description, anempirical fact without a specific mechanism.
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Causality of phenotypic variation inMendel s experiment is best described as:
a)Genetic determination
b)
Environmental determination
c)
Gene-environment interaction
d) Developmental noise
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Mendels other hybrid crosses confirm the 3:1 characterorphenotype ratio in inbred dominant and recessive charactercrosses
Mendels data demonstrates that genetic facts are
statistical facts. You can not predict a exact phenotypebut in a breeding design you can assign an expected
probability .
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MENDELS FIRST LAW: EQUAL SEGREGATION OF ALLELES
Mendels Model
(1)
Inherited germinal or pollen particles for each character orgenesmayhavegenes in different states calledalleles(variation)
(2) Individuals have 2 copies of each gene (gene pairs). If thestates of each gene are the same they are calledhomozygotes(pp or PP), if alleles are different they are calledheterozygotes(Pp).
(3) Each parental gene segregatesrandomly into a gamete(spermor eggs) or individuals in a pair are segregated into different
gametes.(4) Parental sex causesgene copies to recombineforming the F1and F2 offspring, which have allele pairs from both parents.
(5) Individual offspring have two copies of each allele, either oneof which may or may not be dominant (P) or recessive (p).
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P
p
0.5 purple gametes inbreeding population
P: Monohybrid Cross : white (pp) and purple (PP)flowers
0. 5
wh
ite g
am
et e
sin
b re
ed
ing
p o
p u
latio
n
Punnett SquareModel of equal segregation andrandom recombination
The breeding population consists of equal numbersof white and purple parents, hence,
you expect 50% p alleles, 50 % P in the F1
F1
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0.5 P
0.5 p All Ppdiploids
purple gametes in thebreeding population
P: Reciprocal monohybrid cross (pp x PP)
whi t
ega
m e
tes
b re
ed
ing
p o
p u
latio
n
Punnett SquareModel
F1 Offspring Expectationbased on equal segregationand random recombination. All heterozygotes
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P p
P
p
0.5 1/2
0.5
1/2
Pp x Pp
F1 PunnettSquare
Inbreed (heterozygote)individuals
F2expected
values
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P p
P
p
PP1/4
Pp1/4
Pp1/4
pp1/4
0.5 1/2
0.5
1/2
Pp x Pp
F1 PunnettSquare
Inbreed (heterozygote)individuals
F2
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Terms to define: Monohybrid cross, genes, alleles, allele
frequency, dominance, monohybrid, homozygote,heterozygote genotype, breeding design, inbreeding andoutbreeding.
Know: genetic models (I-IV);Mendel 1: the monohybrid cross breeding design, includingthe meaning of inbreeding and outbreeding, first and secondfilial crosses; Mendels first law -what it means, PunnettSquare.
Monohybrid breeding design - Parentals, expectations F1, F2