The document discusses the concepts of ontogeny and phylogeny. Ontogeny refers to the development of an individual organism from fertilized egg to adult form, while phylogeny refers to the evolutionary history and relationships between groups of organisms. It describes Ernst Haeckel's inaccurate biogenetic law which stated that ontogeny recapitulates phylogeny, or that development replays evolutionary history. While some connections exist, ontogeny does not generally recapitulate phylogeny as was once believed.

1. SUBMITTEDTO,
DR.S.VISWANATHAN
HEAD DEPARTMENT
OF MICROBIOLOGY
SUBMITTED BY
ARULTHIVYA K
I M.SC MICROBILOGY

2.  A famous but scientifically inaccurate phrase, “ontogeny
recapitulates phylogeny,” was coined by German biologist Ernst
Haeckel (1834–1919) in the 1860s.
 Ontogeny, from the Greek for “origin of being,” is the growth of
any multicellular (many-celled) living thing from fertilized egg to
adult form.
 Phylogeny, from the Greek for “origin of a tribe or kind,” is the
evolutionary history of a group, often pictured as a family tree.
 Therefore, the saying “ontogeny recapitulates phylogeny,” also
called the biogenetic law, can be restated as “the growth of an
individual replays the evolutionary history of its species.”

3.  The biogenetic law asserts, for example, that if all vertebrates
(animals with spinal columns) evolved from fish, then early in their
development all vertebrate embryos should resemble fish.
 If the next stage in the evolution of mammals was amphibian, all
mammal embryos should next resemble amphibians.
 This replay of ancestral forms would continue until the adult form
of each animal is reached. The process described by the biogenetic
law is referred to as recapitulation.
 For over a century, biologists have known that the biogenetic law
is at best a partial truth. There are many connections between
ontogeny and phylogeny, but the biogenetic law is too simple.
Ontogeny does not, in general, recapitulate phylogeny.

4.  Ontogeny (also ontogenesis) is the origination and development
of an organism (both physical and psychological, e.g., moral
development, usually from the time of fertilization of the egg to
adult.
 The term can also be used to refer to the study of the entirety of
an organism's lifespan.
 Ontogeny is the developmental history of an organism within its
own lifetime, as distinct from phylogeny, which refers to
the evolutionary history of a species.
 Another way to think of ontogeny is that it is the process of an
organism going through all of the developmental stages over its
lifetime.

6. Gametogenesis:
Formation and maturation of sperm and egg.
Fertilization:
Fusion of sperm and egg to produce diploid(2N) zygote
Cleavage:
Mitotic cell division of early embryo , eventually forming a blastula or
blastodisc.
Gastrulation:
Migration and displacement of single layer of surface cells , still
mitotically active , so that three distinct layers are usually formed

7. Migration and displacement of single layer of surface cells , still mitotically active , so
that three distinct layers are usually formed
Ectoderm = external layer. Gives rise to skin and nervous system
Mesoderm = middle layer. Gives rise to muscles , circulatory system , most of the
skeleton , excretory and reproductive systems , etc.
Endoderm = innermost layer. Gives rise to digestive tract and derivatives ( lungs , liver ,
etc..)

8. Organogenesis
continuous masses of cells in the 3 primary germ layers become split
into smaller groups of cells – each of which will develop into a specific
organ or body part of the animal.
Growth and differentiation
growth of organ rudiments and acquisition of structure and
physiochemical properties allowing them to function as adult
structures
Neurulation
In developing vertebrate offspring , a neural tube is formed through
either primary or secondary neurulation. Some species develop their
spine and nervous system using both primary and seconddary
neurulation , while others use only primary or secondary neurulation.
In human fetal development , primary neurulation occurs during weeks
3 and 4 of gestation to develop the brain and spinal cord
Then during weeks 5 and 6 of gestation , secondary neurulation forms
the lower sacral and coccygeal cord

10.  Phylogeny is the evolutionary history of a species or group.
There are about 100 million species living on earth today.
 The morphological and biochemical evidence suggests that
all the organisms are genetically related.
 The genealogical relationships of the organisms can be
represented in the form of an evolutionary tree known as the
phylogenetic tree. In this, the species or groups are
organized in such a way that helps to know how they evolved
from the common ancestors.
 Phylogeny helps us know how the genes, genomes and
species evolve. It is useful for fundamental and numerical
applications.

11.  The phylogenetic tree is also known as the cladogram. The species or
the groups are found at the tips of the lines known as the tree
branches.
 The evolution of species evolved from a common ancestor is
exhibited by how the branches connect.
 The branch points represent the most recent common ancestor of all
the groups descended from that common point.
 Some cladograms are blocky, while the others are diagonal. However,
the orientation of the tree does not change the information.
 In a phylogenetic tree, if two species have the more common recent
ancestor, they are more related than those with a less recent
common ancestor.

13. Classification
 The Linnaean classification of species is known with the help
of phylogeny. Based on the sequence data, more accurate
descriptions of patterns of relatedness are available.
Forensics
 The DNA in case of a crime scene or paternity disputes is
assessed by phylogeny.
Identification of the origin of Pathogens
 Phylogenetic approaches can be used to know about a new
pathogen outbreak. It helps to know the species the
pathogen is related to and the source of its transmission.

14. Conservation
 Phylogeny helps the conservation biologists to
make decisions about which species they should try
to prevent from extinction.
Computing and Bioinformatics
 The algorithms developed for phylogenetics are
also used in software development in other fields.

16.  https://en.m.wikipedia.org/wiki/ontogeny
 https://en.m.wikipedia.org/wiki/ontogeny-and-
pylogeny
 https://pediaa.com/difference-between-
ontogeny-and-pylogeny/