Download Genetic Principles

GeneticPrinciples
AdvancedGenetics
Jan.232017
YangLI
Mendel
• Lawofsegregation
allelessegregatefromeachotherintheformationgametes.
• Lawofindependentassortment
genesfordifferenttraitsassortindependentlyduringthe
formationofgametes.
Q1:Besidespeas…
• Hieracium
• Seedsproducedbyapomixis;ofmaternalorigin
• Mirabilis
• Honeybees
• Mice
• Cirsium
• Geum
• Maize
• Livestocks
• Peaweevil(Bruchus pisi)
Q2:Mendel’sexperimentalapproach
Threenewprocedures
• Definedphenotypes
• Separategenerations
• Quantitativeandstatistical
relationships
Effective,dueto:
• Simpleinterpretationofratios
• Follow-upexperimentstosupporthis
hypothesis
Q3:Fisher:countstoogoodtobetrue?
• e.g.6022:2001istoocloseto3:1
• Theprobabilityofafitthisgoodbychanceis.00007
• PossiblethatMendel’ssamplesizewaslargerthanhereported.
Q4:Chillout,Fisher
• OtherinvestigatorshaverepeatedMendel’sexperimentsandreport
rationscloserandfurtherthanMendel’s
• Overallimpression:resultsfitjustfinewithexpectation.
MutationMuller
Q5:Theoriginsofgenes
• Donewgenesarise(denovomutations)orisall
geneticvariabilitypre-existing?
• The‘presenceandabsence”hypothesisexplained
newlyarisenphenotypesastheresultofgeneloss.
Q6:Typesofmutations
• Autosomalrecessivemutationsareharder
tostudyindiploidorganismsbecauseboth
allelesmustbepresenttoobservethe
phenotype.
• Autosomaldominantandsex-linked
mutations areeasiertostudyindiploid
organisms.
Q7:Muller’sexperimentaldesign
• Establishedaquantitativestudyof
mutationwith
1.anobjectiveindex
2.Aclassofmutationsfrequentenough
togivestatisticallysignificantvalues.
Q7:TheClB chromosome
• AllowedeasiercountingoflethalX-linkedmutations
• Invertedsequence=noCrossingover
• Recessivelethalgene
• Dominant“Bar”mutation
Q8:Ionizingradiationinducesmutations
• MullerusedDrosophila
• X-rays
• Radiationaffectsthe
germline,notonlythe
soma
• Stadler usedbarley
• X-raysandradiumexposure
• Germlineandsoma.
Linearrelationshipbetweendoseandmutationrate(bothgroups)
Sutton:Thechromosomesinheredity
Theconnection
betweenheritability
traitsand
chromosomes.
Q9:Chromosomesandallelemorphs
• Suttonraisesthepossibilitythatallelescorrespondtoa
partofachromosome.
• Ifanallelomorph correspondedtothewhole
chromosome,thenumberofdistinctcharacteristicsof
anorganismcouldnotexceedthenumberof
chromosomes.
Q10:Bateson’s3casesofnon-Mendelian
inheritance
• 1)Blendedinheritance
- Multiplegenesinfluenceatrait.
• 2)Firstcrossesthatbreedtrue
–Allgametesofaself– fertilizingspeciesareidenticalduetothe
absenceofthereductiondivision(noseparationofhomologous
chrmosomes)
• 3)“Falsehybrid”
-Lossofonesetofparentalchromosomesintheoffspring,resulting
inahaploidorganism(parthenogenesis)
Q14:Peacrosses
• F1
• Rr
• red
• F2
• RR:Rr:rr 1:2:1
• Red:white 3:1
Geneticsvocabulary
• Homozygous –
thetwoallelesata
locusareidentical
• Heterozygous – the
twoallelesatalocus
aredifferent
• Aneuploidy –
thepresenceofan
abnormalnumberof
chromosomes
Geneticsvocabulary
• Linkage – theclose
proximityoftwoormore
locionachromosome
• Linkagedisequilibrium–
thenon-random
associationofallelesat
twoormorelocithat
descendfromasingle,
ancestralchromosome
Geneticsvocabulary
• Synteny – theconservationofblocksoforderwithin
twochromosomesthatarebeingcompared,usually
betweenspecies
Geneticsvocabulary
• Expressivity – Thedegreetowhichaphenotypeisdisplayedin
individualsofagivenphenotype
• Penetrance – thepercentageofindividualsofagivengenotypethat
displayaphenotypeabovethecutoff
Geneticsvocabulary
• Pleiotropy – asinglegenemaycontributetomultiple
phenotypes
• Epistasis – agenemayinteractwithormodifythe
phenotypeofanothergene
Geneticsvocabulary
• Epigenetics –heritable(throughmitosisormeiosis)changes
ingeneregulationratherthanchangesintheDNAsequence
itself
Geneticsvocabulary
• Inheritance – thewayin
whichgenesarepassed
tothenextgeneration
• Heritability – the
proportionofthe
parentalphenotypic
variancepassedon
geneticallytothe
offspring
Geneticsvocabulary
• Hardy-Weinberg
equilibrium– inthe
absenceofevolutionary
influences(selection,
drift,migration,etc.),the
genotypeandallele
frequenciesina
populationwillremain
constant
• Evolution – thechangein
thefrequencyofallelesin
apopulationovertime