Mendelian Genetics and its Extensions

This PPT intends to explore the foundation of genetics with special reference to Mendelian genetics.

1. Mendelian Genetics and its extension
By
N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia ( W.B) India
GENETICS

2. HYBRIDIZATION

3. GENETICS ?
Theproverbgoes-likebegetslike’.Themotherclaimsthe
characteroftheoffspringareidenticaltograndmotherandthe
fatherclaimsthecharactersbearsbytheoffspringidenticalto
grandfather.Isittrue?Questionsrelatingtothenatureandthe
basisfortherelationshiphaveoccupiedthethoughtsofman
sincethedawnofthehumancivilization.Initially,thecredit
goestothealmighty,Godbutsystematicattemptstoseek
answerstothesequestionsbeganonlyinthepost–renessiauof
theEuropeandonlyintheeighteenthcentury,severalscientists
begantoexplorethetruthbehindthetruth.Thestudiesleadthe
foundationofthejourneyoftheanotherdomainofnatural
scienceandthecreditgoestoGregorJohannMendel(1822-
1884).Thebranchofbiologydealswiththecauseand
consequencesalongwiththetransmissionofcharactersare
calledgenetics.

4. TERMINOLOGIES
Factor:Mendelpresumedthatacharacterisdeterminedbya
pairoffactorsordeterminers(hereditaryunits)presentineach
cellsoftheindividual.Theseareknownasgenesinmodern
genetics.
Allelesorallelomorphs:alleleisaGreekwordwhichmeans“
belongingtooneanother”.Itisusedtorefertoonememberof
genepair.AccordingtoMendel,twogenesrepresentingtwo
alternativeofacharacterarepresentontwoseparate
chromosomesbutasthecorrespondingloci.Forexample,ina
genepairTt,Tispresentinonechromosomeandtontheother
homologouschromosomebutatthesamelocus.,Eachofthem
iscalledanalleletotheother.Tisanalleletotandviceversa.
Locus:Thephysicallocationofaparticulargeneina
chromosomeiscalledlocusorloci.

5. TERMINOLOGIES
Dominance:Onememberofanallelicpairofgeneshasthe
abilitytomanifesttoitselfwhiletheexclusionoftheother
member.Thisisknownasdominance.Thetraitbearingthis
characterisknownasdominanttraits.Acapitalletter(T)is
usedtodenoteit.
Recessive:Oneoftheallelicpairofgeneshavingnoabilityto
manifestitselfduringcrossingisknownasrecessive.Thetrait
bearingsuchcharacteriscalledrecessivecharacteras
expressedassmallletter(t).
Genotype&Phenotype:thegeneticmakeupofanorganismis
calledgenotypeandthephenotypeindicatesitsexternal
appearance.Apureroundgenotypeis(RR)orheterozygous
(Rr).
Homozygous&Heterozygous:Twogenesidentical(TT)for
particularcharacteriscalledhomozygousbuttwocontrasting
genepairforparticularcharacter(Tt)iscalledheterozygous.

6. GREGOR JOHAN MENDEL
Bornin1822,MoravianearBrunninAustriainapoorfamily,
Mendelinitiallyjoinedaspriestandthenstudiedphysics,
Mathematics,PhilosophyInViennauniversity.Hereturnedto
Brunn,appointedassubstituteScienceteacheralongwith
priestinalocalchurch.Hebegantocollectpeaseedsforhis
experimentforsevenyears.Hepresentedhisfindingsbefore
theNaturalHistorySocietyOfBrunnattwoofitsmeetings
entitledapaper‘Experimentsinplanthybridization’in1866;
Mendelbecamemuchmoreinvolvedinhisinquisitivenessto
explorethebeautyofthetransmissionofcharacters.Hediedon
1884attheageof62.Heproposedthreeimportantprinciples-
Lawofdominance,Lawofsegregation&lawofIndependent
assortment.Afterhisdeath,threescientists,HugodeVries,
Correns&Tschermakrediscoveredhisfindings.

7. WHAT DID MENDEL DO?
ThemainobjectsofMendelexperimentsbasicallybasedonthe
determinationofpurelinecharactersfollowedbythecross
pollinationofthebisexualplantstoestablishthedesired
outcomesinarepeatedlymanner.Hechosegardenpea,Pisum
sativumwithwelldefinedcharactersforitsdifferent
advantageslikeavailabilityseveralcharactersintwo
contrastingforms,charactersrelativelylarge,plantsbi-sexual,
selffertilizedandhomozygouscharacter,durationofcrop
comprisessingleseason,easytogrowandhandleetc.
i.Crossedtwoparentshavingcontrastingcharactersby
artificialcrosspollinationusingemasculationofbisexualplants
followedbybaggingofthedesignedfemaleone.
ii.Themaleandfemalegametesuniterandomlytoformzygote
iii.Iftwovarietiesarecrossed,onlyonetraitisexpressed
calleddominantandothersremainhiddencalledrecessive.

8. WHAT DID MENDEL DO?
Hegavetheformulaefordeterminingthenumbersofi0
differenttypesofgametesproducedbyF1,ii)different
genotypesinF2,iii)homozygousgenotypesandiv)
heterozygousgenotypesinF2forthesegregationoffactors
anticipatedfortheexpressionofthephenotypictraits.
Hemadeacleardistinctionbetweentheexternalappearance
(Phenotype)andthegeneticmakeup(genotype).Heclassified
theF2individualswithdominantphenotypeintopureand
hybridformsonthebasisoftypesinthesucceedingprogenies.
Onthebasisoftheobservationofthesinglecharacters
crossing(Monohybrid),heexploredthreeimportantoutcomes-
Lawofunitcharacters-Eachcharactercontrolledbyonefactor
Lawofdominance-Phenotypicallyexpressedtreatedas
dominance.
Lawofsegregation-Segregationsofthetwofactorshavingthe
chanceduringgameteformation.

9. MONOHYBRID CROSS
Ahybridthatdifferswithrespectofonepairofgenesiscalled
amonohybrid.InthePeaplant,asmooth(SS)seedflower
plantcrossedwithawrinkledseed(ss)fivesF1hybrid(Ss)that
areallsmoothinseedshape.Suchacrossisknownas
monohybridcross.Ithasinfactageneforsmoothandagene
(allele)forwrinkleseedshape.Smoothseedshapeare
dominantoverwrinkleseedshape.TheSSpeasarepurefor
smoothshapeandwouldproduceallsmoothseedoffspring.
Thesameheldtrueforthesspeasinrespectofwrinklelness.
Thesspeaseedsarephenotypicallysmoothbutcarriedthe
factorforwrinklenessasarecessive.Twoofthesecrossed
wouldagaingiveSS.Ss,Ssandss.The3:1ratioisa
phenotypeandthegenotyperatio(SS:Ss:ss)is1:2:1asshown
inthenextslide.

10. CHECKER BOARD
Male/Female S s
S SS(Homozygous,
dominant)
Ss(Heterozy7gous,
dominant)
s Ss(Heterozygous,
dominant)
ss(homozygous,
Recessive)

11. MENDEL FINDINGS
Fromtheaboveexperiment,Mendelconcludedthreeimportant
principles-
Lawofunitcharacters,
Lawofdominance,
LawofSegregation.
Lawofunitcharacter-Thistheoryadvocatesthepresenceof
factorresponsiblefortheexpressionofaparticularcharacteras
experimentallyprovedbyMendel.Thepodshapeeither
smoothorroughisdeterminedbythepresenceofunitfactors
viz.S&s.IfSSorSs,thephenotypicexpressionwillbe
smoothbutifitbecomesss,thenitwillberoughinpure
recessivehomozygousform.Thus,thelawofunitcharacters
statesthefactorresponsiblefortheexpressionofanyunit
character.

12. DETERMINATION OF
HOMOZYGOUS OR HETEROZYGOUS
Astoldearlier,thecharacterhavingphysicalmanifestationis
knownasphenotypiccharacterandthehiddenfactor(gene)
responsiblefortheexternalmanifestationiscalledgenotypic
character.Buthowitbecomesconfirmsthehomozygousor
heterozygousnatureoftheexpressionbecausethisisvery
importantcluesbeforeconductinganytypeofhybridization
programmeirrespectiveorplantsoranimalhybridization
programme.Thetestwhichisconsultedinthisregardknown
asthetestcrossanditisalsoatypeofbackcrossasthe
crossingisdoneinbetweenthetraitsofwhichthetesting
individualderivedfromtheparentone.So,itisusuallycalled
thatalltestcrossesarebackcrossinotherhand.Nowquestion
comesthedefinitionofthetestcrossandhowitisconductedto
havetheresultinthisregard.

13. TEST CROSS
AcrossbetweentheF1hybridandastrainhavingtherecessive
formofcharacterisknownastestcross.Thepurposeofthetest
crossistoobtainevidencethatsegregationfortheallelesasa
singlegeneintheF1hybridproducestwotypesofgametesin
equalfrequencies.Accordingtothelawofsegregation,theF1
(Tt)fromacrossbetweenTT&ttseededpeavarietieswould
producegametesofT&tinequalfrequencies.Thestrainwith
recessivetrait(tt,dwarf)usedintestcross,wouldproduceonly
onetypeofgametesi.et.UnionofthegametesfromF1with
thosefromthetestcrossparent,therefore,isexpectedto
producetwotypeofseeds.Tt(tall)andtt(dwarf).The
frequenciesofthesetwotypesofseedsareexpectedtobe
equal.Mendeldevisedandmadesuitabletestcrossinthis
study.Hefoundthattheratiointestcrossprogenywasalways
1dominant:1recessivethatindicatetheappearanceof
characterinequalfrequencies.

14. TEST CROSS

15. ALL TEST COROSS ARE BACK CROSS BUT
NOT VICE VERSA
Amethodofverificationofanunknowngenotypeisthe
behaviorofitsallelesintestcrosses.Itisacrossingthe
genotypebacktothehomozygousrecessiveparent.Generally,
whenF1iscrossedwithanyoftheparentirrespectiveto
dominantorrecessiveiscalledbackcross.So,inthislogic,all
testcrossesarebackcrossbutallbackcrossesarenottestcross
unlesstheF1iscrossedwithhomozygousrecessiveparent.To
testthevalidityofthetheoryofinheritance,Mendelusedatest
crossinwhichtheF1plantswerematedtorecessive
homozygous.TheF1plantheterozygousforasinglepairof
allelesshouldproducetwotypeofgermcellsinequalnumbers
followingmeiosisandsoyieldshalfofthedominantprogeny
andhalfoftherecessiveprogenyasfoundintheaforesaid
crossbutifitisdonewithhomozygousdominant,allwillhave
dominantcharacters.

16. LAW OF INDEPENDENT ASSORTMENT
Accordingtothislaw,thesegregationoftwoormore
charactersinthesamehybridisindependenttoeachother.
Thusanyalleleofonegeneisequallylikelytocombinewith
anyalleleoftheothergeneandpassintothesamegamete.
Independentsegregationoftwogenesproducesfourdifferent
typeofgametesinequalproportion.Arandomunionamong
thesegametesgiveriseto16possiblezygotes.Thezygotes
yieldaphenotypicrationof9:3:3:1whichisknownastypical
dihybridratio.Thegenotypicratiois1:2:2:4:1:2:1:2:1.Asthe
twodifferenttraitswereconsideredinthiscontext,itiscalled
dihybridtest.Theindependentsegregationoftwogenesmeans
thatoneofthetwoallelesofonegenecancombineanyoneof
thetwoallelesoftheothergeneandpassintothesamegamete.
Thefrequenciesofallsuchcombinationsareequal.Theresult
wasconfirmedbythehybridizationoftheconsiderationoftwo
charactersasfollows.

17. DIHYBRID EXPERIMENT
Acrossbetweentwoparentsdifferingintwotraitsorinwhich
onlytwotraitsareconsideredcalleddihybridcross.Mendel
raisedseparatelytwopurevarietiesofgardenpeas,onewith
yellowcotyledon,roundseedandanotherwithgreen
cotyledon,wrinkledseed.Fromthecrossbetweenthesetwo
parental(P)generationplants,theoffspring’sintheF
1
generationwereallwithyellowcotyledonandroundseed.
WhentheseF
1plantswereself-fertilized,theoffspring’sofF
2
generationwereoffourtypesintheratio9:3:3:1–
(a)Yellowcotyledon,roundseed(b)Yellowcotyledon,
wrinkledseed(c)Greencotyledon,roundseedand(d)Green
cotyledon,wrinkledseed.Theoffspring’sshowedthattwo
pairsofcontrastingcharacterscombinedineverypossibleway.
Mendelcarriedoutdihybridexperimentswithallthechosen
charactersindifferentcombinationsandgotthesimilarresults.

18. DIHYBRID CROSS

19. EXPLANATION
1.Astheparentalplantswerepure,sotheirgenotypeswillbe
homozygous–YYRRandyyrrproducingYRandyrgametes
respectively.
2.TheF
1dihybridwillbeheterozygousforboththetraits
(YyRr).
3.AsalltheF
1plantswerewithyellowcotyledonandround
seed,soalleleYforyellowcotyledonisdominantoveralleley
forgreencotyledonandalleleRforroundseedisdominant
overallelerforwrinkledseed.
4.Theappearanceofallthefourpossiblephenotypic
combinationsinF
1intheratio9:3:3:1ispossibleifthetwo
pairsofcharactersarebelievedtobehaveindependentofeach
other.Eachpairofcontrastingcharactersbearnopermanent
associationwithparticularothercharacter.

20. EXPLANATION
5.IftheF
1plant(YyRr)producesonlyparentalgametes(YR,
yr),theninF
2onlytwotypesofphenotypes(parental)are
expected.ButtheappearanceoffourtypesofphenotypesinF
2
(twoparentalandtwonewtypes)confirmstheproductionof
fourtypesofgametes(YR,Yr,yR,yr)inequalfrequency.
Theappearanceoftwonewtypesofphenotypiccombinations
–yellowcotyledon,wrinkledseedandgreencotyledon,round
seedinadditiontoparentalphenotypiccombinationsrequires
theproductionofYrandyRgametesinadditiontoYR,yr
gametesbyF
2plants.
6.ThusthealleleYmaybeassociatedwiththealleleRaswell
asrinequalfrequency,givingrisetoYRandYrgametes
respectively.Similarly,thealleleymaybeassociatedwiththe
alleleRaswellasrinequalfrequencygivingrisetoyRand

21. EXPLANATION
yrgametesrespectively.Thusfourtypesofgametesviz.’,YR,
Yr,yRandyrwillbeproducedintheratio1:1:1:1.
7.Thesefourtypesofgametes(bothmaleandfemale)will
uniteinsixteenpossiblecombinationstoproduceninetypesof
genotypesintheratio1:2:1:2:4:2:1:2:1andfour
typesofphenotypesintheratio9:3:3:1.
8.Thesimilarratioswillresultevenifthecharactersare
presentindifferentparentalcombinations:yellowcotyledon,
wrinkledseedXgreencotyledon,roundseed.Thisfurther
provesthattheinheritanceofindividualcharacteris
independentoftheothercharacteristics.
Mendelwasfortunateinselectinghisexperimentalmaterial.It
isself-fertilizingspeciesbutfertilehybridscanbeproduced
andallthesevencharacterschosenbyhimshowedindependent
assortmentwithoutanylinkage.

22. GENETIC EXPLANATION
Theroundyellow&wrinkledgreenvarietiesusedasparents,
maybeassignedasRRYY&rryy
TheroundyellowwillproduceallRYgametes&green
wrinkledwillproducerygametes,
TheunionbetweenRY&rygametesfromtwoparentswill
produceRrYyprogenyinF1,
IntheF1,bothRr&Yywillsegregateatthesametimeand
thesegregationwilltakeplaceindependentlytoeachother.
IntheF2generation,theselfinginbetweenthetwoF1will
producefourdifferentkindofgametes-RY,Ry,rY&ryand
thecrossinginbetweenthe4gameteswillproduce16different
typeofcombinationhaving4altogetherphenotypictraitsas
toldearlier.Itindicates,thatthetwopairsofcharactersmay
staytogetherbutcanbeassortedindependentlyiftheyhavethe
pleasuretodoso.

23. DIHYBRID TEST CROSS
MendeltestedhistheorybycrossingtheF1(double
heterozygous)toacompletelyrecessivei.ewrinklegreen.If
Mendel’shypothesiswascorrect,theprogenywouldbeoffour
kinds:roundyellow,roundgreen,wrinkleyellowandwrinkle
greeninarationof1:1:1:1asexpectedfromdihybrid
backcrosstothedoublerecessiveparent.Mendelobtained,in
thetestcrossprogeny,55roundyellow(RRYY),51round
green(RrYy),49wrinkleyellow(rrYY)and53wrinklegreen
(rryy).Thisisapproximatelythepredictedratioof1:1:1:1.The
frequenciesoffourclasseswas¼,¼,¼&¼yieldingthe
aboveratio.Dihybridtestcross(involvinggenessegregate
independently)doactuallyyieldfourtypesofprogenyinthe
ratioof1:1:1:1.Thistestalsousedtoknowthegenotypeofthe
dominantpairoftraits-eitherhomozygousorheterozygousat
theonsetofbreedingprogrammeindesigningAnd
development.

24. DIHYBRID TEST CROSS

25. CHROSOMAL BASIS OF INHERITENCE
Mendelfindingswasinthemiddleofthe19
th
centurywhenthe
experimentalgeneticswasnotintherighttrackduetolackof
modernappliancesandknowhows.Intheearlyofthe20
th
century,
Mendelfindingswasrediscoveredbyanumberofhisfollowersand
thedarknessabouttheinheritanceoftheacquiredcharacterandits
transmissionbecamecrystalclear.Nowadays,Mendeldiscoveryhas
beenexplainedonthebasisofthechromosomalbasisofinheritance
pattern.
Thephenomenonofsegregationhasbeenexplainedonthebehavior
ofchromosomesduringmeiosis.AccordingtoMendelism,thetwo
allelesseparateandgotodifferentgametes.IntheF1hybrid,one
alleleofonegeneislocatedinonechromosomeandtheotherallele
ispresentintheothermembersofhomologouschromosomes.
Duringnormalcelldivision.Twohomologouschromosomespair
duringzygoteneandeachsplitlongitudinallytoformtwochromatids
beingjoinedwitheachotherindifferentpoints.

26. PHYSICAL BASIS OF SEGREGATION
Thetwobivalentshomologouschromosomeseachcarrying
oneofthetwoalleles,startmovingtooppositepolesat
anaphaseI,asaresult,eachpolehashaploid(N)numberof
chromosomes.Thetwosisterchromatidsofeachchromosome
separateandmigratetooppositepolesinanaphaseII.Thecell
dividesintotwohalvesbutdonotseparateafterthefirst
meioticdivision.BytheendofthetelophaseII,theoneparent
cellproducesfourdaughtercells(tetrad).Eachhavingone
chromatidfromeachhomologouspairofchromosomes.Two
ofthefourcellsreceivethesisterchromatidsfromoneofthe
twohomologueswhiletheothertworeceivethesister
chromatidsfromotherhomologues.So,thetwoofthefour
cellsreceivethesamealleleofthegene,whiletheremaining
twocellscontainotheralleleoftheallelepair.Thus,eachof
thetwonucleiformedafterthemeioticdivisionhasonlyoneof
thetwoallelesofeverygene.

27. CROSSING OVER FOR SEGREGATION
Atprophasestage,eachhomologouschromosomesofthepair
hastwosisterchromatids.Occasionally,non-sisterchromatids
ofahomologouspairofchromosomesexchangesimilar
portionsoftheirchromosome,aphenomenoncalledcrossing
over.Whensuchcrossingovertakesplacebetweenthegenes
andcentromere,thesisterchromatidsofthechromosomeasa
resultnowcarrydifferentallelesofthegeneinquestion.
Therefore,aseparationofthetwochromosomesofa
homologouspairatanaphaseIdoesnotleadtosegregateofthe
twoallelesofthegene.Thetwoallelesofthegene,however,
segregateatanaphaseIIwhenthesisterchromatidsofeach
chromosomemovestotheoppositepoles.Insuchsituation,
thetwoallelesofagenesegregateduringsecondmeiotic
division.Thus,thesegregationofthehomologous
chromosomesduringmeiosisisthereasonbehindthe
segregationofthetwoallelesofagenelocatedinidentical
positioninthehomologouschromosomes.

28. CROSSING OVER

29. PHYSICAL BASIS OF INDEPENDENT
ASSORTMENT
Independentassortmentfortwogenescanbeexplainedby
assumingthatthetwogenesarelocatedintwodifferent
chromosomes.Thetwoallelesofagenewillbelocatedinthe
twohomologuesoftheconcernedchromosome.Independent
separationofthesetwopairsofchromosomesatanaphaseIof
meiosiswillleadtotheindependentassortmentofthegenes
locatedinthem.Twoallelesofageneoccupythesameposition
intwohomologuesofachromosome.Thefixedlocationofa
geneinaspecificlocationiscalledlocus(loci).During
prophase–I,thetwochromosomespairscontainingrlocus(R
&r)andy(Y&y)locusformtwobivalents.Randrwillbe
presentinonebivalentwhileYandywillbepresentinanother.
Iftheorientationsofthetwohomologuespairsareindependent
atmetaphase-I,therewillbe4fourpossiblecombinationsofthe
twochromosomepairs-RY,Ry,rY,ryin1:1:1:1.

30. PHYSICAL BASIS OF INDEPENDENT
ASSORTMENT
Thus,anindependentmovementofthetwopairsof
chromosomes,eachcarryingallelesofonegene,leadstoan
independentsegregationandassortmentoftheallelesofthe
twogenesinquestion.Theindependentorientationand
movementofchromosomescanbeevidencedunder
microscopebyheteromorphichomologuespairsof
chromosomesinwhichthetwomembersdifferfromeachother
intheirmorphologyandformheteromorphicbivalent.Such
heteromorphicpairofunequalsizewasdiscoveredby
Carothersin1913inaninsectBrachystola.Thus,an
independentseparationoftwopairsofchromosomes,eachpair
carryingallelesofoneofthetwogenes,willleadtoan
independentsegregationoftheallelesofthetwogenes.

31. LIMITATIONS OF MENDEL’S LAWS
1.Mendelassumedthatcharacterscontrolledbyasinglepair
ofgenes.Butgeneinteractionsresultanewtraitormodify
trait.Multiplecharacterscontrolquantitativetraits.
2.IneachofthesevencharactersasstudiedbyMendel,
dominanceofonealleleovertheotherwasrule.However,in
somecases,theF1heterozygouswasintermediateinbetween
thetwohomozygote.Thisshowsincompletedominance.The
idealexampleistheflowercoloroffouro’clockplant-
Mirabilisjalapa;redflowercrossedwithwhiteflowerappears
pinkcolorthatdoesnotfollowtheMendelianrule.
3.Mendelpredictedofonlyonealternativeformsofeach
characterhestudied.Heassumedonlytwoallomorphsofeach
locus.-onedominantandotherrecessive.Butmultiplealleles
existencerejectthisconcept.
4.Mendelsevencharacterswrenfortunatelydistributedin
sevendifferentpairsofchromosomesbutinothercases,

32. LIMITATIONS OF MENDEL ’S LAWS
thisdoesnothappen.Hedidnotfacetheconsequencesof
linkageandcrossingover-thetwomagicofreality.Hadhe
studiedmorecharactershewouldhavecomeupwithmore
complicatedphenomenonoflinkageandcrossingover.So,he
wasquitefortunateenoughtohavetheseinferencesfromhis
experimentandthiswasoneofthecauseandconsequencesof
hisoutstandingperformances.
Mendelassumedthatfactorwasparticulatebuthehadnoidea
aboutitsbiochemicalnatureandthiswasquiteobviousinhis
contemporary.NeitherDNAnorthegeneanditsexistencewas
explored.
Contrastingcharacters,mathematicalknowledge,experiment
withcareandelaboratenessaresomeofthefeaturesforhis
successinthisendeavor.
ThelimitationsofMendelwasanopportunitybyhis
successorstounfoldofnewchapterofinthisdomain.

33. SOME PROBLENS CAN BE ADDRESSED
1.Alltestcrossesarebackcrossesbutnotallbackcrossesare
testcrosses-justify.
2.Determinethedifferentgametesproducedbythefollowing:
a)Aabb,ii)AABbiii)AaBbDdiv)TtrR
3.Inman,browneyes(B)aredominantoverblue(b)anddark
hair®tored(r).Amanhasbrowneyesandredhair.He
marriesawomanwithblueeyesanddarkhair.Givethe
genotypesandphenotypesoftheparentandchildren.
4.Adwarfpeaplantwithyellowseedsiscrossedwithtallplant
withgreenseeds.GivethegenotypesandphenotypesofF1,the
gametesproducedbyF1andthegenotypesandphenotypes
withcheckerboard.
5.Anindividualhavingthreepairsofchromosomeshas
receivedthecentromeres.A,B,andDfromhisfatheranda,b,
anddfrommother.Listthevariouscombinationsof
centromeresobtainingitsgametes.(Considerthecentromeres
asgenes)

34. CONCLUSION
Mendelwasconsideredas“fatherofgenetics’duetohisurge
toexplorethecauseandconsequencesaboutthecauseofthe
biologicalcharactersanditsmodeoftransmissionfollowing
theruleofmathematicsininheritancepattern.WilliamBatson(
1909)stated“Thestudyofhereditythusbecomesanorganized
branchofphysiologicalscience,alreadyabundantinresults,
andinpromiseunsurpassed”.Althoughtheprinciplesof
Mendellaidthefoundationsofgenetics,still,itdevelopedalot
ofquestionsafterthepost-Mendelianresearchoutcomes.
Irrespectiveofmonohybrid,dihybridortrihybridexperiments,
differentotherissueslikeincompletedominance,lethalfactor,
multiplealleles,pleiotropy,co-dominance,complementary
geneinteraction,supplementarygeneaction,epistasis,
hypostasisetcarenowbecomecrystalclearasfarasthecause
andconsequencesthattobeexploredinthenextPPT.

35. THANKS FOR YOUR JOURNEY
References:
1.Googleforimages,
2.PrinciplesofGenetics-Basu&Hossain,
3.AtextbookofBotany(VolIII)Ghosh,Bhattacharya,Hait
4.FundamentalsofGenetics-B.D.Singh,
5.ATextbookofgenetics-AjoyPaul
Thispresentationhasbeenmadewithoutanyfinancialinterest,
toenrichopensourceofinformation.Thepresenter
acknowledgesthefollowingstodevelopthisPPT.