1. PRESENTATION ON PARTHENOGENESIS

2. ‘No fertilization’ :

3. HISTORY OF PARTHENOGENESIS:
Parthenogenesis was first recognized in 1745 by CHARLES BONNET {SWISS, }.
JACQUES LOEB {German, } stimulated parthenogenesis in sea urchin and frog eggs by artificial means in 1900.
G.PINCUS in 1936 artificially produced the first known parthenogenetic offspring in a mammal {rabbit}.

5. DEFINITION: Parthenogenesis is a natural form of asexual reproduction
Growth and development of embryos occur without fertilization.
It is a component of apomixis.

6. OCCURRENCE:
Parthenogenesis is found in many invertebrates such as rotifers and arthropods.
Crustaceans , insects and arachnids {spider, mites} also exhibit parthenogenesis.
It also occurs in some vertebrates {rock lizards and birds}.

7. TYPES OF PARTHENOGENESIS:
Natural parthenogenesis:
Complete{ obligate } parthenogensis
Incomplete {cyclic} parthenogenesis
Paedogenetic parthenogenesis
Artificial parthenogenesis.
1. Natural Parthenogenesis:
In certain animals the parthenogenesis occurs regularly, constantly and naturally in their life cycles and is known as the natural parthenogenesis.
The natural parthenogenesis may be of two types, viz., complete or incomplete

8. Complete Parthenogenesis:
Certain insects have no sexual phase and no males. They depend exclusively on the parthenogenesis for the self-reproduction.
This type of parthenogenesis is known as the complete parthenogenesis or obligatory parthenogenesis.
EXAMPLES:
Rotifers:
In bdelloid rotifers, females reproduce exclusively by parthenogenesis
In monogonont rotifers, females can alternate between sexual and asexual reproduction .
Caucasian rock lizard:
This lizard from caucasian region of soviet union reproduces only by parthenogensis,always producing females by this process .
There are no males at all.

9. Rotifers:
Rock lizard:

10. Incomplete parthenogensis:
The life cycle of certain insects includes two generations, the sexual generation and parthenogenetic generation, both of which alternate to each other.
In such cases, the diploid eggs produce females and the un-fertilised eggs produce males.
This type of parthenogenesis is known as the partial or incomplete or cyclic parthenogenesis.

11. Aphids :

12. Examples:
Aphids:
Aphids have many successive generations of females develop from unfertilized eggs in spring and summer.
In late summer both sexes are formed by parthenogenesis
Now the females mate with males and lay fertilized eggs that survive the cold winter season and hatch into females in the next spring to continue parthenogenesis.

13. Honey bee :

14. Honey bee:
The queen honey bee is inseminated by a male called drone during her nuptial flight .
The sperms are stored in pouch that communicate with her genetal tract .
She lays fertilized eggs by opening the valves to let some sperms to escape.
The fertilized eggs developed into females {queen and worker bees}.
The unfertilized eggs developed into male bees .
Spermatogenesis in drones is peculiar in lacking reduction division.

15. Life cycle of honey bee :

16. Rotifers:
Certain rotifers lays two types of eggs :amictic and mictic .
The amictic eggs are diploid and can’t be fertilized .
Mictic eggs are haploid .
If mictic eggs are not fertilized they produce males parthenogenetically and if they are fertilized they developed into female.
Birds:
All the chicks produce from unfertilized eggs are males and may be fertile as adults.

17. Birds :

18. Wasps:
Some species of wasps produce alternately a parthenogenetic generation , one which developed from unfertilized eggs.

19. The complete or incomplete type of natural parthenogenesis may be of following two types:
1. Haploid or arrhenotokous parthenogenesis;
2. Diploid or thelytokous parthenogenesis.
1. Haploid or arrhenotokous parthenogenesis:
In the arrhenotokous parthenogenesis, the haploid eggs are not fertilised by the sperms and develop into the haploid individuals.

20. Haploid and diploid

21. Examples:
a. Insects:
(i) Hymenoptera (bees and wasps),
(ii) Homoptera,
(iii) Coleoptera (Micromalthus debilis),
(iv) Thysanoptera (Anthothrips verbasi).
b. Arachnids:
Arachnids, e.g., ticks, mites and certain spiders (Pediculoides ventricusm)
c. Rotifers:
Rotifers, e.g., Asplanchne amphora.

22. 2. Diploid or thelytokous parthenogenesis:
In the diploid parthenogenesis, the young individuals develop from the un-fertilised diploid eggs.
Types:
(i) Ameiotic Parthenogenesis:
Sometimes during the oogenesis, first meiotic or reduction division does not occur but second meiotic division occurs as usual.
Such eggs contain diploid number of chromosomes and develop into new individuals without the fertilisation.
This type of parthenogenesis is known as apomictic or ameiotic parthenogenesis and occurs in weevils and long-horned grasshoppers.

23. (ii) Meiotic Parthenogenesis:
Certain eggs develop by the usual process of oogenesis but at certain stages diplosis or doubling of chromosome number and production of diploid eggs occur.
Such eggs develop into the diploid individuals and this phenomenon is known as the meiotic parthenogenesis.

24. Diplosis:
The diplosis of the diploid thelytoky may occur by the following methods:
(i) By Autofertiiisation:
In certain cases, the oocyte divides meiotically up to the formation of ootid or ovum and secondary polocyte.
The ootid and the secondary polocyte unite together to form a diploid egg which develops into a new individual, e.g.,Crustacea.
(ii) By Restitution:
Meiosis 1 lacks cytokinesis.
The chromosome of both the nuclei formed by meiosis go over the spindle of meiosis 2 forming a diploid ovum and diploid polar body.
The diploid ovum developed into a diploid individual parthenogenetically.

25. Diplosis:

26. Paedogenetic parthenogenisis:
Larvae of some insects lays eggs which develop parthenogenetically into new generation of larvae.
Such parthenogenesis among larvae is termed as paedogenetic parthenogenesis.

27. Paedogenetic parthenogenesis:

28. 2.Artificial parthenogensis:
The eggs which always develop into the young individuals by the fertilisation sometimes may develop parthenogenetically under certain artificial conditions. This type of parthenogenesis is known as artificial parthenogenesis. The artificial parthenogenesis may be induced by various chemical and physical means.

29. Illustrating artificial parthenogensis:

30. A. Physical means:
The following physical means cause the parthenogenesis:
(i) The range of temperature {30°C to 0-10°C } may induce parthenogenesis in the eggs.
(ii) Electrical shocks can cause parthenogenesis.
(iii) Ultraviolet light can cause parthenogenesis.
(iv) When the eggs are pricked by the fine glass needles the development of young ones takes place parthenogenetically.

31. B. Chemical means:
The following chemicals have been found to cause parthenogenesis in the normal eggs:
1.Chloroform;
2. Hypertonic and Hypotonic sea waters;
3.Chlorides of K+, Ca++, Na+, Mg++, etc.;
4.Acids such as butyric acid, lactic acid, oleic acid and other fatty acids;
5.Fat solvents, e.g., toluene, alcohol, benzene and acetone;
6. Urea and sucrose.

32. Experimental parthenogenesis:

33. Significance of Parthenogenesis:
1. The parthenogenesis serves as the means for the determination of sex in the honey bees, wasps, etc.
2. The parthenogenesis supports the chromosome theory of inheritance.
3. The parthenogenesis is the most simple, stable and easy process of reproduction.
4. The parthenogenesis eliminates the variation from the populations.
5. The parthenogenesis is the best way of high rate of multiplication in certain insects, e.g., aphids.

34. {Cont.}
6.The parthenogenesis causes the polyploidy in the organisms.
7. The parthenogenesis encourages advantageous mutant characters.
8. The parthenogenesis checks the non-adaptive combination of genes which may be caused due to the mutation.
9. Due to the parthenogenesis, there is no need for the organisms to waste their energy in the process of mating.
10. The parthenogenesis avoids the sterility in the races.

36. Thanks