What is Reproduction???
Reproduction (or procreation or breeding) is the biological
process by which new individual organisms – "offspring" –
are produced from their "parents".
Reproduction is a fundamental feature of living organisms
which involves the transmission of genetic material from one
generation to the next ensuring the survival of species over
long periods of time.
Asexual reproduction is a type of reproduction which does not
involve the fusion of gametes or change in the number of
The offspring that arise by asexual reproduction from a single
cell or from a multicellular organism inherit the genes of that
Organisms produced are referred as genetically ‘clone’.
Benefits of Asexual Reproduction
Fission can be simply called as break down.
It is a primitive type of reproduction.
During the fission and organism just divides itself a-mitotically or
mitotically in two almost equal halves giving rise two off-springs.
After the processes the parent cell loses its identity.
On the basis of axis of division, fission can be-
On the basis of number of off-springs produced, fission can be-
When an organism produces more than two cells after fission.
Here the nucleus of the organism replicates first and then the
cytokinesis occurs . at one time more than two daughter cells are
It take place in Plasmodium.
Endogenous or Internal Budding:
Such type of budding is generally common in Sponges like Sycon &
Here the budding take place inside the body of organism.
Such type of buds are called Gemmules and can be defined as tough
coated dormant coated clusters of embryonic cells.
Gemmules of Spongilla and Ephydatia
Differences between Fission and Budding:
• No Buds or external outgrowths
• Buds or external outgrowths
• Two Young ones are formed of
• A single young one forms much
smaller to its parents.
• Parent body loses its identity • Parents body maintains its
• Division of body is symmetrical. • Division of body is
Fragmentation is the process of breaking a piece of organism followed by
cell division of mitosis.
The broken part can become an independent adult.
The reproduction of Spirogyra, a green Algae well-known examples of
Besides Spirogyra this is very common among cyanobacteria, molds, lichens.
The fragmentation capacity depends on the complexity of the organism. It
may or may not be intentional and may occur naturally or by predators.
Regeneration is a modified form of fragmentation. It is known as a process that
makes genomes, cell organs, organisms and ecosystems resistant after
alterations or damage.
All species that live on earth can regenerate, but only a few species use it as a
method of asexual reproduction, thus producing new individuals for their body
Flat planar worms are highly adapted with regeneration capabilities due to their
asexual reproduction methods. Among vertebrates, tail amphibians
(salamanders and newts) and certain lizards (geckos) are highly adapted to
regenerate their limbs, tails, jaws, eyes and certain internal organs.
As they are more complex multicellular animals, they cannot use regeneration
to reproduce or as an asexual reproduction method.
Starfish also have the same ability to regenerate their arm, but unlike
amphibians and tail lizards, the lost arms of starfish could regenerate a whole
Sporulation or Spore formation:
Spore are single celled minute propagules produced by several
organisms specially fungi, which are able to develop into an complete
Spores can be form,
Difference between Fragmentation and
• Take place in multi-cellular
organism having simple body
• Take place in fully-differentiated
multi-cellular organism having
complex body organization.
• Each and every piece of body
produces new organism.
• Each and every piece of body
may not develop in a new
• No specialized cells are
• Specialized cells proliferate and
form a mass of cell. Each cell of
mass differentiate to new cells
Vegetative propagation is a form of asexual reproduction of a
Vegetative Propagation defined as a mode of asexual reproduction
where non-reproductive parts of plants are involved in the
production in new organism.
Cutting Layering Grafting Tissue
Natural Vegetative Propagation
Natural vegetative propagation happens when plants grow and
develop naturally without human interventions.
Vegetative propagation take place with the help of several plant
structures including Roots, Shoots & Leaves.
Vegetative plant structures that arise from plant stems
include rhizomes, runners, bulbs, tubers, and corms.
Tubers can also stretch from roots.
Plantlets emerge from plant leaves.
Vegetative propagation may occur
naturally through the development of
Rhizomes are modified stems that
typically grow horizontally along the
surface of or beneath the ground.
Rhizomes are storage sites for growth
as Protein and Starches.
As rhizomes extend, roots and shoots
may arise from segments of the rhizome
and develop into new plants.
Certain grasses, lilies, irises, and
orchids propagate in this manner.
Edible plant rhizomes include ginger
Rhizome of Ginger
Runners or Stolon
Similar to rhizomes in that they exhibit
horizontal growth at or just below the soil's
surface. Unlike rhizomes, they originate
from existing stems.
As runners grow, they develop roots from
buds located at nodes or their tips.
Intervals between nodes (internodes) are
more widely spaced in runners than in
New plants arise at nodes where shoots
develop. This type of propagation is seen in
strawberry plants and currants.
Runners of Strawberry
These are vegetative organs that may
develop from stems or roots.
Stem tubers arise from rhizomes or
runners that become swollen from
The upper surface of a tuber produces
a new plant shoot system (stems and
leaves), while the bottom surface
produces a root system. E.g., Potatoes
Root tubers originate from roots that
have been modified to store nutrients.
These roots become enlarged and may
give rise to a new plant. E.g., Sweet
potatoes and Dahlias
Shoot Tuber of Potato
These are the round, swollen parts of a
stem that are typically found underground.
Within these organs of vegetative
propagation lies the central shoot of a new
Bulbs consist of a bud that is surrounded
by layers of fleshy, scale-like leaves.
These leaves are a source of food storage
and provide nourishment to the new plant.
Examples of plants that develop from
bulbs include onions, garlic, shallots,
hyacinths, daffodils, lilies, and tulips.
Bulb of Garlic
These are enlarged bulb-like underground
These vegetative structures store nutrients in
fleshy, solid stem tissue and are typically
externally surrounded by papery leaves.
Due to their physical appearance, corms are
commonly confused with bulbs.
The major difference is that corms contain
solid tissue internally and bulbs have only
layers of leaves.
Corms produce adventitious roots and possess
buds that develop into new plant shoots. Plants
that develop from corms include crocus,
gladiolus, and taro.
Corm of Gladiolus
Artificial Vegetative Propagation
Artificial vegetative propagation happens when plants grow
and develop naturally with human interventions.
Human beings exploits the properties of plants of being
There are several methods that can be applied for Vegetative
Propagation in Plants
A part of a plant, typically a stem or leaf, is cut off and
Adventitious roots develop from the cuttings and a new
Cuttings are sometimes treated with hormones before being
planted to induce root development.
Example- Rose plants are generally planted by cuts of their
It is simply a method of
joining the vascular tissues of
two different plants one over
In grafting, a desired cutting
or scion is attached to the
stem of another plant that
remains rooted in the ground.
The tissue systems of the
cutting become grafted into or
integrated with the tissue
systems of the base plant over
Types of Grafting
This method involves bending
plant branches or stems so
that they touch the ground.
The portions of branches or
stems in contact with the
ground are then covered with
Adventitious roots or roots
that extend from structures
other than plant roots develop
in the parts covered by soil
and the attached shoot (branch
or stem) with new roots is
known as a layer.
Types of Layering
These are vegetative structures that
develop on some plant leaves.
These miniature, young plants arise
from meristem tissue located along
leaf margins. Upon maturity,
plantlets develop roots and drop
They then take root in the soil to
form new plants. An example of a
plant that propagates in this
manner is Kalanchoe.
Plantlets may also develop from
the runners of certain plants such
as spider plants.
Leaf of Bryophyllum
This technique involves the
culturing of Plant cells that
may be taken from different
parts of a parent plant.
The tissue is placed in a
sterilized container and
nurtured in a special medium
until a mass of cells known as
a callus is formed.
The callus is then cultured in a
hormone-laden medium and
eventually develops into
plantlets. When planted, these
mature into fully grown
Steps of Tissue
Sexual reproduction involves formation of the male and
female gametes, either by the same individual or by
different individuals of the opposite sex.
These gametes fuse to form the zygote which develops to
form the new individual.
Advantages of Sexual Reproduction:
Reproductive Cycle in Plants:
Annual Plants: These plants complete their life cycle in one year and then
must start from seeds or cuttings the next year. Look for annuals near the
beginning of the frost-free planting season. E.g.,
Biennial Plants: These plants have a two-year life cycle, and this category
is lesser known category. Biennial plants grow leaves, stems and roots the
first year, then go dormant for the winter. In the second year the plant will
flower and produce seeds before dying. E.g.,
Perennial Plants: These plants live for at least three years assuming wild
animals and poor weather don’t kill them first. They will come back year after
year from their own overwintering roots even though their foliage may die to
the ground after frost. Perennials are sold throughout and often beyond the
growing season. E.g.,
Breeding in Animals:
Seasonal Breeders: They reproduce at particular period of the year such as
frog, lizards, most birds, deer, etc.
Continuous Breeders: These animals can breed or mate throughout the
year. This includes humans and apes (chimpanzees, gorillas, orangutans, and
gibbons), who can have a child at any time of year.
Among continuous breeders, the majority of mammals become sexually-
receptive (express estrus) and ovulate spontaneously at defined intervals. The
female will only allow the male to mate during a restricted time coinciding with
The females of placental mammals exhibit cyclical changes in the activities of ovaries
and accessory ducts as well as hormones during the reproductive phase.
Hence, Mammals can exhibit either-
Oestrus Cycle Menstrual CycleOR
Differences between Oestrous Cycle & Menstrual
Oestrus Cycle Menstrual Cycle
• It occurs in non-primates such as
cows, dogs, etc.
• It occurs in primates (monkeys, apes
and human beings) only.
• It consists of a short period of
oestrous or heat (e.g., 12-24 hours in
cow) followed by anoestrous or
• This cycle consists of menstrual
phase, proliferative phase and the
• Blood does into flow in this cycle. • Blood flows in the last few days of
• The broken endometrium is
• The broken endometrium is passed
out during menstruation.
• Sex urge is increased during
• Sex urge is not increased during
• Female permits copulation only
during oestrous period.
• Female does not permit copulation
during menstrual phase of the cycle.
Events of Sexual Reproduction:
Events in Sexual
Gametogenesis refers to the formation of male and female gametes, (Gametes;
Gametes can be defined as a mature haploid male or female germ cell which is able to unite with
another of the opposite sex in sexual reproduction to form a zygote.
Gametes can be:
• Homo-gametes or Isogamous: Gametes are similar in appearance and size,
and can not be categorized into male and female gametes. E.g., Cladophora
• Hetero-gametes: Gametes are not identical in size, shape and appearance, and
hence can be categorize into male and female gametes.
1. Gametogenesis contd..
Hetero-gametes can be:
Anisogamous- Both the male and female gametes are motile but female
gametes are greater in size. E.g., Chlamydomonas and members of
Oogamous- Here male gametes are motile and female gametes are non-
motile, female gametes are usually greater in size. E.g., Human beings
Here, male gametes are called as antherozoid or sperm while female
gametes are called ovum or egg.
Sexuality in organisms: Phenomenon of occurrence of male
and female sex organs in same or different body.
Homothallic & Monoecious:
Represent bisexual condition.
Heterothallic & Dioecious:
Represent unisexual condition.
• There is another condition too called Hermaphrodite, that represent
condition when a organism is bisexual but exchange their gametes
• In unisexual flowers, Male is called staminate and female is called
Cell division during Gametogenesis:
In an organism having haploid type of parental body
gametogenesis take place by the Mitotic Division. For
example, Monera, fungi, algae and bryophytes.
In an organism having diploid type of parental body
gametogenesis take place by the Meiotic Division. For
example, Gymnosperms and Angiosperms and in Animals
and Human Beings.
In these organisms specialized cells called meiocytes or
gamete mother cells under go meiosis to give rise gametes.
To facilitate the events of fertilization it is required that male and female
gametes come to each other.
The purpose is fulfilled by the process called Pollination in the case of
plants while copulation in the cases of animals.
In majority organisms male gamete is motile where as female is
stationary. Exceptions , a few fungi and algae both types of gametes are
Gametes posses flagella for the movement and require a medium.
In algae, bryophytes and pteridophytes, water serve as the medium for
To compensate loss of male gametes during transport, the number of
male gametes produced is several thousand times the number of female
It is a very crucial step of Sexual reproduction.
It is the fusion of male and female gametes to give rise a zygote.
The process is also called as Syngamy.
Fertilization can be:
External and Internal Fertilization
External Fertilization Internal Fertilization
Syngamy occurs outside of the
body of organisms.
Syngamy occurs inside of the
body of organisms.
Large number of gametes (male
& female) are released into
Number of ova are less, but
large number of male gametes
E.g., Bony fish, Amphibians Etc. E.g., Birds, mammals, earthworm
Post- Fertilization Events:
The events after zygote formation is called post-
This include formation of embryo and development
of embryo into a complete organism.
The Zygote and its Fate:
Zygote is a single cell formed by the fusion of two (male and female)
Every organism including human being begin its life from single cell
It is an important link between the previous and next generations.
As gametes are haploid, zygotes are always diploid.
In organisms belonging to fungi and algae, zygote develops a thick
wall that is resistant to desiccation and damage and undergoes in a
period of rest before germination.
In organisms exhibiting haplontic life cycle, zygote undergoes
meiosis and forms meiospores that further propagate to develop
new organisms which are haploid.
In higher organisms it undergoes several mitotic divisions and gives
rise an embryo.
The formation or development of embryo from a single celled
zygote is called embryogenesis.
It take place as result of division mitotic division in zygote and
further rapid multiplication of cells and the differentiation of
Cells are divide to increase their number, while cell
differentiation results in the modification of cells to give rise
specialized group of cells- tissues and organs to form new
Tissues Organs Organisms
Types of Animals on the basis of development of
On the basis of development of zygote inside or outside the body organisms
1. Viviparous- Gives birth directly to a young one. E.g., most of the
mammals including Human Beings.
2. Oviparous- Lay fertilized or unfertilized eggs. The eggs are covered by
a calcareous shell and laid in a safe environment for incubation after which a
young one hatches out. E.g., Birds & reptiles.
o Chances of survival of viviparous organisms are greater because of proper
Post-fertilisation Changes in Flowering
In flowering plants, fertilization and hence formation of zygote
take place inside the ovules.
After fertilization, the sepals and petals of flowers wither (dry) and
fall off. In the members of Solanaceae (E.g., Brinjal) sepals
remain attached with fruit.
As the zygote develop into embryo, the ovules develop into seeds
Ovary develops into fruit and its wall become thick and fleshy and
Seeds may undergo dormant condition and cease their metabolic
activities and during favorable condition germinate into new
Unusual Modes of Reproduction:
Apomixis: It is an asexual reproduction that occurs without
fertilization and not involving meiosis. One example of apomixis is
the apomictic parthenogenesis. It its one in which the egg cell is
produced through mitosis. It then develops directly into an embryo
without the prior fertilization. E.g., Rubus (brambles or blackberries),
Parthenogenesis: Reproduction from an ovum without
fertilization, especially as a normal process in some invertebrates and
lower plants. Cyclic parthenogenesis is well displayed in aphids.
Parthenogenesis never produces viable embryos, though, because
unfertilized eggs lack specific instructions about gene expression from
Neotany: This is the condition in which an organism reaches
maturity without losing all of its juvenile characteristics.
Typical examples would include becoming sexually viable while still in
a larvae stage or retention of gills in an adult. E.g.,