What is Parthenogenesis ?
Parthenogenesis is the development of female gamete into embryo without
any gamete contribution from the male gamete.
It works widely in a large number of plant kingdom, but in animal
kingdom it is not widely established.
It occurs frequently in certain orders of insect eg. Hymenoptera
(bees & wasp) ,Homopteran, Coleopteran (beetles), Rotiferal and
lower crustaceans.
Parthenogenesis occurs as a regular process in some groups, while in
some groups it alternate with sexual generation. It may occurs by
artificially as well as naturally.
Induced Parthenogenesis
In many animals which usually reproduce sexually, the egg of that
animals can be activated or induced by artificial method. Such type of
method to start the development without fertilization. Such type of
parthenogenesis is called artificial or induced
parthenogenesis.
eg. Sea Urchin can be induced successfully if it is treated with some
salt solution or organic acid, electric shock or shacking them in sea
water.
Stimulation Of Induced Parthenogenesis
A variety of agents can activate the egg to develop into embryo. This
are:
1. Physical Stimulus- It is provided by breaking the egg with the help of fine
needle.
2.Temperature- Stimulus may be provided by temperature
shocks.
3.Chemical Stimulus- The unfertilized eggs may be induced to divide by treating them
with chemical .Such as Lactic acid, Butyric acid, Ether and Acetone
etc. can be used for induction of egg to divide .Hypo and Hyper-tonic
sea water and foreign blood serum can also initiate the egg to
divide.
4.Stimulus Provided By The Sperm Entry- The entry of sperm can
also initiate divisions in the egg without contributing it's nucleus.
eg. When sperm from Annelids are allowed to enter the egg of Echinoderms
(Sea Urchin),The nuclei of sperm and the egg do not fuse but the egg
starts dividing.
Significance Of Artificial Parthenogenesis
1.Means Of Reproduction- It ensures the continuity of race
when sexual reproduction fails to develop into embryo.
2.A Device For High Multiplication- In some species like
Aphids ,bees and wasp parthenogenesis is alternate with the sexual
generation. The multiplication rate varies fast during
Parthenogenesis life cycle, indicating that it affords a rapid mode
of multiplication.
3.Advantageous Combination Of Genes- Parthenogenesis
encourages combination of characters of genes originated by
mutation.
4.Disadvantageous Combination Of Genes- All the mutagenic
changes and their combination are not useful to the organism, So
natural selection in the Parthenogenetic form will lead to the
elimination of non-adaptive combination of genes.
5.Elimination Of Diverse In Population - The offspring which
are developed Parthenogenetically are more alike to the parents,
where as sexually developed offspring exhibit differences from their
parents, So their is elimination of diverse in population.
Natural / Obligatory Parthenogenesis
It is a regular mode of reproduction in some colonial insect like
Honey Bee (Apis indica). Fertile Queen produces two types of eggs, The
fertilized and the unfertilized egg.
The larva from fertilized eggs develop either in fertile Queen when it
feed into royal jelly or into workers when it feed on mixture of
pollen and nectar. The unfertile eggs develop into Drawn male
parthenogenetically. Natural Parthenogenesis may be of two type-
1. Complete/ Cyclic Parthenogenesis- Some insect have no sexual
phase i.e. no male individual. They depend exclusively on
parthenogenesis for reproduction .
This type of parthenogenesis is called as Complete Parthenogenesis. eg.
Epiperipatus imthurni.
2. Incomplete / Non-Cyclic Parthenogenesis- The sexual generation alternate with parthenogenetic generation.In such
cases the fertilized eggs gives female and unfertilized eggs gives male.
eg. Apis indica.
Haploid Parthenogenesis
In this parthenogenesis the haploid eggs are not fertilized by sperm and
developed into a haploid individual. In this case all haploid individuals
are always male and the diploid individuals are always female.
This is seen in the male honey bees and some flowering plant. Rather than
that it is also found in four groups of insect
Haploid Parthenogenesis-
1. Hymenoptera
2. Homopteran
3. Coleopteran
1. Hymenoptera
2. Homopteran
3. Coleopteran
4. Thysanoptera- Arachnids likes ticks, mites and certain spiders and
rotifers.
Diploid Or Thelytokous Parthenogenesis
Chromosome reduction occurs in normal manner and the diploid chromosome
number is restored by the fusion of two haploid nuclei. In the
parthenogenesis the young individual developed from the unfertilized egg.
Diploid parthenogenesis may be of two types-
1. Amitotic Parthenogenesis- Some times during the oogenesis first meiotic or reduction division
does not occurs but second meiotic division occurs. Such eggs contain
diploid number of chromosome and develop into new individuals without
fertilization. This type of parthenogenesis can be seen in long horn
grasshopper ,weevils, Crustacean (Daphnia pulex) etc.
2. Meiotic Parthenogenesis- Certain eggs developed by the usual process of oogenesis but at
certain stages of life cycle diplosis or doubling of chromosome number
occurs. Such eggs developed into diploid individual.
Process Of Diplosis
1.Auto fertilization- In certain cases the oocytes divides meiotically up to the formation of ova. But the ovum unite together to form a diploid egg which develop into new individual. eg. Artemia salina ( Crustacea).
2.Restitution- Sometimes in primary oocytes karyokynesis forms a
nucleus of secondary oocyte. But the karyokinesis is not followed by
cytokinesis.
The chromosomes of both daughter nuclei are arranged on the equator and
undergo second meiotic division to form a diploid ovum.
The Diploid ovum develops into parthenogenetic diploid individual. eg.
Insects of Hymenoptera ,Nematids.
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