Genetics-Cytoplasmic Inheritance

This PPT intends to explore the basic idea of cytoplasmic inheritance and maternal effects in the transmission of traits.

1. Extra-chromosomal Inheritance :
Chloroplast mutation: Variegation
in Four o’clock plant; Mitochondrial
mutations in yeast; Maternal
effects-shell coiling in snail;
Infective heredity-Kappa particles
in Paramecium

2. PRESENTED BY
N. Sannigrahi, Associate Professor
Department of Botany
Nistarini College, Purulia (W.B) India

3. TheMendelianinheritancepatternmostlyadvocatesthe
characterstransmittancefromparentstooffspringviathe
gametesandthelateronthishasbeenconfirmedbythecourtesy
ofthechromosomespresentinthenucleus.Butinduecourse,
evidenceofthetransmissionofcharacterswasexploredby
CorrenswhiletheinvestigationofcharactersinMirabilisjalapa
andlateronbyBaurinPelargoniumzonale.Theytermedthis
inheritancepatternasPlastidinheritance.Lateron,anumberof
geneticistslikeRhoades,Sonneborn,RuthSagerandRs&Plaut
alsodemonstratedthistypeofinheritancepatternonthedifferent
otherexperimentalmaterials.Thisisnowdefinedascytoplasmic
inheritancepattern.Inthisconsequences,thecharacterofonly
oneofthetwoparents(usuallythefemaleone)istransmittedto
theprogeny.Asaresult,reciprocalcrossesexhibitconsistent
differencesforsuchcharactersandthereislackofsegregationof
traitsinthesubsequentgenerations.

4. Genesinthechromosomeshaveundoubtedlybeenprovedtobe
responsibleforthetransmissionofthevarioushereditary
characterswhichinturnarelocatedinthenucleus.Butinrecent
years,therehavebeenfoundsomeevidenceswhichsuggestthat
inheritanceofcharactersoccurbysomeself-perpetuatingor
replicatingbodieslikeplastidsandmitochondriawhichpossess
theirownequipmentforsynthesizingforDNAandproteins
presentinthecytoplasmandnotinthechromosomespresentin
thenucleus.Thisparticulartypeofmechanisminwhich
cytoplasmicparticlesorinclusionstakepartintransmissionof
charactersfromgenerationtogenerationconstitutescytoplasmic
inheritance.Thetotalselfreproducinghereditarymaterialof
cytoplasmistermedasPlasmonlikethegenome(whichrefersto
thetotalgenecomplementofanhaploidsetofchromosomes)of
chromosomesandsuchunitsofcytoplasmichereditarymaterial
arecalledcytoplasmicgenesorplasma-genesorPlasmons.

5. ThecytoplasmichereditaryunitsaredenotedbyGreekletters-
alpha,beta,gamma,sigmaandsoon,incontrasttothe
chromosomalgeneswhicharedenotedbyRomanletters-a,b,c,
dandsoon.Whileconsideringvariousexamplesofcytoplasmic
inheritanceithasbeenassumedthatthecytoplasminthesperm
cellispresentinveryminutequantityandmostlyitisinlarger
quantityintheegg.So,wecouldexpectthatplasma-genes
mostlywilltransmitonlythroughtheeggcytoplasmratherthan
minutesperm.Thus,plasma-genesforvarioussizesand
charactersarelikelytobesupposedonlyintheeggcytoplasm.
(i)Itismoreorlessmaternalinheritancei.e.,onlyfemale
contributetowardsinheritanceandtherefore.
(ii)Theresultofreciprocalcrossesarenotthesame.Inthese
features,extra-nuclearinheritancecontrastssharplyfromnuclear
inheritance.Onlyinfewcases,mostlyinplants,evidenceshave
beenfoundthatsometraitsorcharactersaretransmittedthrough
cytoplasm.Suchtraitsaretransmittedthroughthefemaleline
only.Eachsetofnucleargenesissometimes

6. designatedasgenomeandallthehereditarymaterialstransmitted
throughthecytoplasmisreferredtoasplasma-genes,cytoplasmic
genes,cytogeneses,extranucleargenesorextrachromosomal
genes.
MATERNALEFFECTS:Thedevelopmentofsomecharactersin
severalorganismsiseithergovernedormarkedlyinfluencedby
thegenotypeoftheparent-knownasmaternaleffects.Such
characters,aregovernedbynucleargenes.Butduetomaternal
effect,theyshowthefollowingfeatures:
1.ReciprocaldifferencesinF1,
2.Which,inmostcases,disappearinF2;
3.AconsiderablesmallervariationinF2ascomparedtothatin
F3.Insomeextremecases,theremaybenosegregationinF2.
Insuchcases,phenotypicsegregationisevidentonlyinF3
gebneration.Manyimportantcharactersofbothplantsand
animalsshowmaternaleffects,ofwhichsomeoftheexamples
arestatedbelowforstrengtheningthisbiologicaluniqueness.

7. CYTOPLASMIC INHERITANCE

8. CHLOROPLAST INHERITANCE
Inheritanceofplastidcharacterduetoplasmageneslocatedin
theplastidisknownasplastidinheritance.Mostofthestudies
inthisregardbasicallybasedonthestudiesofchlorophyll
variegationinleavesbutrecentstudiesbasedonRFLPand
SEMareextensivelyusedtoexplorethisthought.Variegation
referstothepresenceofwhiteoryellowspotsonthevariable
sizeonthegreenbackgroundofleaves.Mutantplasmagenes
affectingchloroplastsarefoundinthedifferentcultivated
plantslikebarley,wheat,maize,pea,tobaccoandmanyother
ornamentalplantsofeconomicimportance.Thepresentstudy
hasbeendoneontheleavesoffouro’clockplanteithergreen,
whiteorvariegatedleavesasstatedbelowandthiscanconfirm
thematernalinheritancetosupporttheconceptofplasmagenes.

9. Findings of Correns In Mirabilis jalapa
Leaf phenotype of the
branch used as Female
Leaf phenotype of the
branch used as male
Leaf phenotype of the
F1 progeny
Green Green Green
Do White Green
Do Variegated Green
White Green White
Do White White
Do Variegated White
Variegated Green Green. White &
variegated in variable
ratios in each of the case
Do White
do Variegated

10. EXPLANATION
Letuspayaglancetotheprevioustabletoexplorethebeauty
ofthetransmissionoftheleafphenotypeoftheplant,Mirabilis
jalapaasobservedbyCorrens.Hemadereciprocalcrossesin
allpossiblecombinationsamongtheflowersofthesethree
typesofbranches.
1.Whentheflowersfromthegreenbranchusedasfemale,all
theprogenyweregreenirrespectiveofthephenotypeofthe
maleparent.
2.Similarly,whentheflowersfromthewhitebranchusedas
female,alltheprogenywerewhiteirrespectiveofthe
phenotypeofthemaleparent.
3.Inthethirdconsequences,thefemalevariegatedbranches
determinethephenotypeoftheF1irrespectiveofthemale
parentphenotype.Butintheprogenyfromthedifferentcrosses
involvingflowersfromvariegatedbranchesasthefemale
parent,green,whiteandvariegatedplantswererecovered.

11. OBSERVATION & COMMENT
Theresultsconfirmtheplasmagenedirectsthecolor
combinationoftheleafoftheaforesaidplant.Proplastids
generallyproducetheplastids.Proplastidhavingmutant
plasmagenedifferentiateintocolorlessabnormalplastidswhile
thenormalalleledevelopnormalplastid.Thematernal
transmissionofplasmagenesinhigherplantscanbeexplained
onthebasisofunequalcontributionofmaleandfemale
gametestothecytoplasmofzygote.Asperthebiological
mechanismsofthesexualreproduction,eggcellhasa
considerableamountofcytoplasmhavingseveralmitochondria
andproplastidswhilethemalecounterpartsbearseldom
existenceofthetwoorganelles.Severalmechanismsoperated
byinvitrotechniquesofthecellfusionsconfirmsthe
Proplastidoriginfromfemalenotmale.Thisisthebeautyof
thecytoplasmicinheritancefromfemalecounterpart.

12. MITOCHONDRIAL
INHERITANCE IN
Yeast

13. Mitochondria,mostimportantcellorganellesdeservementioning
asitisthepowerhouseofcell&storehouseofenergyalongwith
itsuniquenessasfarastheselfreplicatingnatureduetothe
presenceofselfDNAforitsreplication.Itisoriginatesfrom
preexistingmitochondriaanditbearsmanyplasmagenesinmt-
DNA.Theinformationextractedfromexperimentsconfirmedthat
mitochondriafromonlyoftheparentsaretransmittedtothe
progeny.Therefore,characterscontrolledbythegeneslocatedin
mt-DNAshowscytoplasmicinheritance.CytoplasmicMale
sterility(CMS)indifferentcropslikemaize,jowar,bajraare
someofthetypicalexamplesinthisregard.Mitochondrial
inheritanceinYeastcanenoughtoexplaintheinheritanceof
charactersinthisregardasstatedbelow.Mitochondrialgenomein
Yeastvariesindifferentstrainsupto10000bpintheirgenome
size.ExtensivedeletionscanoccurinmtDNA,incaseofpetite
mutants.Allpetitemutantslackmitochondrialfunctionasitcan
growanaerobicallybutitmaybelethalparticularlyforthe
aerobicplantsandanimals.

14. Allthepetitemutantslackmitochondrialfunctionandtheyareof
threetypes.
1.Nuclearpetites-Producedbynucleargenemutationandthey
abolishmitochondrialfunctionandfollowMendelian
inheritance,
2.NeutralPetites-CharacterizedbytheabsenceofmtDNA,
representanextremesituationandarerecessiveininheritance,
3.Suppressivepetites-Thesemutantshavemuchsmaller
mtDNAs,complexityoftheirgenomerangingfrom0.2%to
36%ofthenormalgenome.Thesepetitemaycontainany
sequenceofmtDNAandthesecopiesmaypresentasseparate
circles,orasamultimericmoleculeinwhichthecopiesare
arrangedintandemasdirectorinvertedrepeats.someofthe
petitesarestablewhileothersareunstableandfurther
rearrangementsoftheirsequenceoccur.
Whenasuppressiveorrhopetiteiscrossedwithawildstrain,in
certainportionofthepetiteisfoundandthewildDNA
disappearsfromthem–suppression.

15. Theproportionoftheprogenyinwhichsuppressionoccur
constitutesthedegreeofsuppressiveness.Thecauseofthe
suppressionishighlysuppressivepetitesisapreferential
replicationofthepetitegenome.Thismaybeduetopresenceof
agreaterconcentrationoforigin-likesequencescalledrep
regions,inpetitemtDNAthaninawildtypemtDNAs.Yeast
mtDNAhasspecificsequencesinvolvedinthereplication
initiationbutpetitemtDNAslackingthissequence.This
indicatesthatallsegmentsofmtDNAinyeastcanbe
independentlyreplicatedsinceanysequenceofmtDNAcanbe
presentinapetite.
NotpnlyinYeast,mitochondriaanditsmutationinmtDNahas
verysignificantroleinhigheranimalslikehumanbeings.
Leber’sHereditaryOpticNeuropathy(LHON),asuddenlost
blindnessinadultsisassociatedwiththemutationofmtDNA
causedopticnervedeathandit’saconsequenceofmaternal
transmission.PearsonMarrow-Pancreassyndromeisalsocaused
bythistypeofmtDNAmutationinhumans.

16. MITOCHONDRIAL INHERITANCE

17. MATERNAL EFFECTS:
SHELL COILING IN SNAIL

18. Yourheartismostlyintheleftsidewhileyourliverisonthe
rightside.Howdoesithappen?Dothereversesituation
happen?Ifyoulookatsnail’sshell,thechancesareof
coilingisattherightdirectionbutveryoftenyoucanfindan
unluckyonethattwistsintheoppositedirection.Thechilarity
ofsnailshellsisanoutwardmanifestationofleft-right
asymmetryandthishasbeenexploredwiththehelpofthe
maternaleffectsoftheinheritancepatternasexperiencedby
thebiologicalworldasfarastheinheritanceofcharacters
patterninthelongpassageofevolution.Anextremeexample
ofthiskindofmaternaleffectsisknowninthesnail,
Limnaea.Inthissnail,thedirectionofthecoilingofitsshell
iscontrolledbyasinglegeneD/d.ThedominantalleleD
producesroght-hande4d(=dextral)coilingwhileitsrecessive
alleledproduceslefthanded(=sinestral)coiling.The
directionofshellcoilinginanindividualisgovernedbythe
genotypeofthefemaleparentandnotbyowngenotype.

19. Oneoftheclassicalexamplesofintricaterelationshipbetween
maternalgenotypeandeggcytoplasm“phenotype”wasstudied
insnailsbySturtevant.Heshowedthattherearetwostrainsof
watersnails(limnaeaperegra)thatdiffereachotherinthe
directionofcoilingofshell.
Lookingintotheopeningoftheshellitcanbeseenthatinone
straintheshellalwayscoilstotheleft(sinistral)whereasinthe
otherstraintheshellalwayscoilstotheright(dextral).Inthe
crossdextral♀xsinistral♂alltheF,progenyhavedextialcoils
implyingthatdextralisdominantoversinistral.However,inthe
F
1,xF
1,cross(i.e.,inbreeding),alltheF
1snailsarealsodextral.
Thereciprocalcross(dextral♂xsinistral♀)producesF
1,
progenythatareallleftcoiler.InthiscaseF
1,xF
1,crossalso
yieldsonlydextralcoils.
Fromtheseexperimentsitbecomesclearthatcoilingofsnailsis
notdeterminedbyindividuals’owngenesbutbythoseofmother.

20. COILING PATTERN & INHERITANCE

21. Infective heredity-Kappa
particles in Paramecium

22. Asstatedearlier,therearethreedistinctclassesofnon-
Mendelianinheritance:
1.Inheritanceofstructureandpatterns,
2.Inheritanceduetoparasites,symbiontsandviruses,
3.Cytoplasmicinheritance.
Anumberofcaseswereonceregardedasclassicalcasesof
cytoplasmicinheritancebutactuallytheyareduetothe
presenceofparasites,symbiontsandviruses.TheKappa
particlesofParameciumisoneofthemostinteresting
episodesdeservementioninginthisregardtoexplorethe
beautyofthebiologyofinheritanceasstatedbelow.
Parameciumisaunicellular.Eukaryoticciliateswidespreadin
freshwaterandthebodyiscoveredwithciliates,contains
twonuclei-micronucleiandmacronucleiandpossess
intracellularbacteriacalledkappaparticlesthatbearhuge
significanceinthisregard.

23. Sonnebornandhisassociateshaveexploredthetransmissionof
cytoplasmicparticlesandtheirrelationtonucleargenesin
Parameciuminfusoriain1943.StrainsofP.aureliacanharbor
some10differentGram(-)bacteriaspeciesincytoplasm,thebest
knownbeingcalledkappaparticles.Maintenanceofeach
bacterialspeciesrequiresaparticularnucleargenesofthehost
paramecium.Thebacteriamaybetransferredfromonetoother
cellbyconjugation.Certainstrainsareknownaskillerstrains,
secreteintothewaterinwhichtheylive,atoxicsubstance
paramecinwhichinjuresandkillsindividualofthesensitive
strainsofthesamespecies.Killerstrainscontainincytoplasm
largeamountsofDNAparticleswhicharecalledKappaparticles.
Kappaparticlesarecalledeither-brightornon-brightdepending
upontheirappearanceunderthelightmicroscope.Brightoneare
believedtoproducethetoxin.AllParameciumcellslacking
kappaaresensitivetoparamecin.Brightkappaisasymbionts
livinginthecytoplasmofParameciumandthenormal
componentofParameciumcells.

24. Kappaparticlesshowcytoplasmictransmissionlikeplasmagenes.
Generally,thereisnocytoplasmicexchangeaccompanyingthe
exchangeofnucleiduringconjugationinParamecium.Therefore
,duringconjugationbetweenonekillerandonesensitive
Paramecium,thesensitivecelldoesnotreceiveanykappa
particles.Asaconsequence,thesensitivecellremainssensitive
aftertheconjugationandproducessensitiveprogeny.But
occasionally,cytoplasmicexchangedoesoccurduring
conjugation;insuchcases,bothanimalsthatparticipatedin
conjugation(exconjugants)receivekappa.Butsubsequent
propagationofkappadependsontheirnucleargenotypesofthese
animals.Kappaparticles,likeotherbacteria,multiplythrough
fission.Howeverkappaparticlesareabletomultiplyonlyin
animalshavinggenotypesKKorKk.Inkkanimals,kappaare
unabletomultiply.Asaresult,theyareeliminatedfromsuch
animals.Thekilleranimalswithkkgenotypeultimatelybecome
sensitiveduetolossoftheirkappaparticles.

25. KAPPA PARTICLES TRANSMISSION

26. Wehavelearnedthemeaningofcytoplasmicinheritance.
CytoplasmicDNAisfoundincertaincellorganellesandcanbe
passedontooffspringstrictlyfromthefemale,male,oramixture
ofbothparents.CytoplasmicinheritanceexamplesareIojapin
maize,pokinessinNeurospora,Oenothera,etc.Therearetwo
typesofcytoplasmicinheritance-Plastidandmitochondrial
inheritance.Cytoplasmicinheritanceisusefulinmanywayssuch
asinexplainingtheroleofvariouscytoplasmicorganellesinthe
transmissionofcharacters,facilitatingtheproductionofhybrid
seeds,andmanymore.Mendelforthefirsttimetriedtoexplore
thecauseandconsequencesofthecharactersofbiologicalentities
alongwiththeirmodeoftransmission.Heproposedthethreeset
ofprinciplesinthisregardandthiskindoftransmissionwas
recognizedasthenucleartransmissionbutMendelneverthought
aboutthecontributionofcytoplasmincharacterstransmissionand
hedidnotinitiallythoughtaboutthematernaleffectsincharacters
transmission.Butpost-Mendelianresearchofferedarecipeof
thoughtinthisregardanditbecomesanawesomeingredients.

27. References:
1.Googleforimages,
2.PrinciplesofGenetics-Basu&Hossain,
3.AtextbookofBotany(VolIII)Ghosh,Bhattacharya,
Hait
4.FundamentalsofGenetics-B.D.Singh,
5.ATextbookofgenetics-AjoyPaul
DISCLAIMER:
Thispresentationhasbeenmadetoenrichopensourceof
informationwithoutanyfinancialinterest.Thepresenter
acknowledgesGoogleforimagesandotheropensources
ofknowledgetodevelopthisPPT.