Sexual Reproduction in an Organisms
In today's class we will achieve the following learning outcomes :
1.Explain how the gametes are produced in different organisms.
2. Understand the transfer of gametes mechanism.
3. State & Explainthe fertilization events.
4. Distinguish between the zygote formation & Embryogenesis.
5. Define parthenocarpy & parthenogenesis.
SEXUAL REPRODUCTION
Definition : It is fusion of male & female gametes, which results in variation in an offsprings.
Sexual Reproduction is divided into three main phases :
1) Pre- Fertilization Events.
2) Fertilization
3) Post - Fertilization Events.
Pre Fertilization events :-
A) Formation of gamete also called as Gametogenesis -
Gametes are formed through meiosis, in which a germ cell / mother cell undergoes two fission, resulting in the production of four gametes (n).
Gametes may be identical ( isogamy) in certain species of algae, fungi & protozoan ormay be more than one morphological type ( anisogamy) found in many green algae of genus Chlamydomonas.
Gametes in animals, some fungi, algae & all higher plants exhibit an advanced form of Heterogamy called "Oogamy". In this, one male gamete is small & motile while the female gamete is large & non-motile.
B) Transfer of Gametes -
In many simple plants like Algae, Bryophyta & Pteridophyta, water serves as the media for gamete transfer.
In higher organisms male gamete is motile & female gamete is stationary. In angiosperms pollen grain are carried to the stigma by agents of pollination. There they germinate to produce pollen tubes
In animals, they follow oestrus cycle/ menstrual cycle, where sperms are ejaculated in the vagina of females
B) Fertilization :
Fusion of nuclei of male & female gamete is called syngamy / fertilization. This process results in formation of a diploid ZYGOTE (2n).
There are various types of fertilization - External & Internal Fertilization.
Exogamy & Endogamy. Differences given already in hand written notes shared to you all earlier).
C) Post Fertilization Events :-
In fungi & algae ---- zygote develops a thick wall which is resistant to destination & damage. It undergoes a period of rest before germination.
In Organisms with Haplontic Life Cycle ------
Zygote undergoes Meiosis to form 4 haploid spores. The spores then grow into haploid individuals
Embryogenesis---- the process of development of embryo from the zygote is called embryogenesis.
Zygote undergoes mitosis & cell Differentiation to form 2.4.8.16....celled embryo. Cell differentiation results in formation of different types of tissues & organs which eventually results in formation of an Organisms.
SPECIAL Cases ---
Parthenogenesis - the female gamete in some organisms develop to form a new organisms without fertilization. Eg: some lizards, rotifers, honeybees, turkey etc.
Parthenocarpy - in plants sometimes natural / artificially induced production of fruits without fertilization of ovules takes place. This results in seedless fruits. Eg:cucumber, bananas, watermelon etc.
With this we come to an end of our first Chapter.
I would like you all to complete your notes further & answer the following Assignment questions in your copy.
1.Explain how the gametes are produced in different organisms.
2. Understand the transfer of gametes mechanism.
3. State & Explainthe fertilization events.
4. Distinguish between the zygote formation & Embryogenesis.
5. Define parthenocarpy & parthenogenesis.
SEXUAL REPRODUCTION
Definition : It is fusion of male & female gametes, which results in variation in an offsprings.
Sexual Reproduction is divided into three main phases :
1) Pre- Fertilization Events.
2) Fertilization
3) Post - Fertilization Events.
Pre Fertilization events :-
A) Formation of gamete also called as Gametogenesis -
Gametes are formed through meiosis, in which a germ cell / mother cell undergoes two fission, resulting in the production of four gametes (n).
Gametes may be identical ( isogamy) in certain species of algae, fungi & protozoan ormay be more than one morphological type ( anisogamy) found in many green algae of genus Chlamydomonas.
Gametes in animals, some fungi, algae & all higher plants exhibit an advanced form of Heterogamy called "Oogamy". In this, one male gamete is small & motile while the female gamete is large & non-motile.
B) Transfer of Gametes -
In many simple plants like Algae, Bryophyta & Pteridophyta, water serves as the media for gamete transfer.
In higher organisms male gamete is motile & female gamete is stationary. In angiosperms pollen grain are carried to the stigma by agents of pollination. There they germinate to produce pollen tubes
In animals, they follow oestrus cycle/ menstrual cycle, where sperms are ejaculated in the vagina of females
B) Fertilization :
Fusion of nuclei of male & female gamete is called syngamy / fertilization. This process results in formation of a diploid ZYGOTE (2n).
There are various types of fertilization - External & Internal Fertilization.
Exogamy & Endogamy. Differences given already in hand written notes shared to you all earlier).
C) Post Fertilization Events :-
In fungi & algae ---- zygote develops a thick wall which is resistant to destination & damage. It undergoes a period of rest before germination.
In Organisms with Haplontic Life Cycle ------
Zygote undergoes Meiosis to form 4 haploid spores. The spores then grow into haploid individuals
Embryogenesis---- the process of development of embryo from the zygote is called embryogenesis.
Zygote undergoes mitosis & cell Differentiation to form 2.4.8.16....celled embryo. Cell differentiation results in formation of different types of tissues & organs which eventually results in formation of an Organisms.
SPECIAL Cases ---
Parthenogenesis - the female gamete in some organisms develop to form a new organisms without fertilization. Eg: some lizards, rotifers, honeybees, turkey etc.
Parthenocarpy - in plants sometimes natural / artificially induced production of fruits without fertilization of ovules takes place. This results in seedless fruits. Eg:cucumber, bananas, watermelon etc.
With this we come to an end of our first Chapter.
I would like you all to complete your notes further & answer the following Assignment questions in your copy.
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