Lecture - 5- gametogenesis and syngamy in plants

Gametogenesis and syngamy in plants

1. Lecture 5-Gametogenesis and syngamy in plants
&
Identical and fraternal twins

2. Sexual Reproduction in Plants
•Inhigherplants,therearetwostagesinvolvedinsexual
reproduction-sporogenesisandgametogenesis.
•Sporogenesisistheformationofspores(microspore–anther
andmegaspore–ovule)
•Gametogenesis:Formationofmaleandfemalegametesfrom
themegasporeandmicrospore

3. Microsporogenesis

4. Megasporogenesis

5. Microgametogenesis

6. Megagametogenesis

8. Double fertilization & Syngamy
Doublefertilization-wheretwonuclei(ofsperm)fromeachofthe
pollentubesgoontofertilizetwoothercells(polarnucleiandegg
cell)thatbelongtotheovary
•Syngamy-fusionofgametes-initiatingthedevelopmentofanew
individual
•Here,maleandfemalegametesproducedbygametogenesis
undergofusiontoformadiploidzygote
•Itcanbenotedthatsyngamyisalsoreferredtoastruefusionand
generativefertilization

9. Classification of syngamy –Based on source of
fusion gametes
•Self-fertilizationorEndogamy:
Theincludesthefusionoftwoformsofgametes
originatingfromthesameparentforexample,Taenia
(tapeworm-veryuncommon
•Cross-fertilizationorExogamy:
Whentwofusinggametesarederivedfrom
separateparentsforexampleinhuman,frog,
cockroach,etc-moregeneral

10. Isogamy
•Thisoccurswhenthegametesthatfusearesimilar
•Anadvancedsystemofrecognitionisusedsoastoavoid
self-fertilization.

11. Heterogamy
•Thishappenswhenthegametesareoftwodifferentsizes-
female-largerwhilemalesmaller
•Also,thenumberofmalegametesismoresothatthereis
anincreaseinthecompetitionandmakesfertilization
likely

12. Oogamy
Thistakesplacewhenthemobilityofthe
gametesaredifferent

13. Difference between Syngamyand Triple
Fusion
Syngamy
Definition
•Thefusionofmaleand
femalegametesduringthe
fertilizationisknownas
syngamy
Development
•Zygoteisproducedwhich
formstheembryo
Result
•Diploidistheendresultof
syngamy
Triple fusion
Definition
•Thefusionofthespermcell
withthetwopolarnuclei
during the double
fertilizationisknownas
triplefusion
Development
•Endosperm cellsare
producedwhichdevelops
intoendosperm
Result
•Triploidistheendresultof
triplefusion

14. Identical and fraternal twins
•Identicaltwinsarederivedfromasingle
zygoteduetoanabnormaldivisionofthe
embryoveryearlyinthedevelopment
•Fraternaltwinsarederivedfromtwo
differentzygotesresultingfrom
fertilizationoftwodifferenteggsby
separatesperms