3. HISTORY OF
PARTHENOGENESIS:
• Parthenogenesis was first recognized in 1745 by
CHARLES BONNET {SWISS,1720-1793}.
• JACQUES LOEB {German,1859-1924} 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}.
4.
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. I. 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.
10. II. 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.
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.
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.
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.
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.
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.
26. III. 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.
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.
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.
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.
