Teratogenesis refers to abnormal development resulting in congenital malformations, affecting about 2.5% of infants. Factors causing teratogenesis, known as teratogens, can be genetic or environmental, involving infections, drugs, malnutrition, and immunization issues. The critical period for teratogenesis occurs during the formation of germ layers and organogenesis, with potential for environmental influences to mimic genetic phenotypes (phenocopies).

1. TERATOGENESIS
By Miss Iram

3. INTRODUCTION
• Normal ontogenetical development resulting into a
normal individual depends upon normal
morphogenesis.
• If there is a deviation from the normal morphogenesis
due to abnormality in the genotype, abnormality in
the differentiation process , abnormality in the
external mileu (environment), morphogenesis
becomes abnormal resulting in a chaotic
development and producing an abnormal embryo
called monster or terata.

4. TERATOGENESIS
• Teratogenesis is made up of greek word Terata- monster & genesis-
formation.
• Teratogenesis is an abnormal development which form an abnormal
organism.
• It is also called as congenital malformation .
• It is a gross structurally deformity present at birth .
• Its incidence is about 2.5% in an infant.
• The term congenital anomaly is reserved for minor congenital disorder
such as deformed fingers

5. TERATOGENS
• Factors which cause teratogenesis are called teratogens.
• Teratogens may be due to genetical factors or environmental agents

6. GENETIC TERATOGENESIS
• Abnormal genes may be inherited from one or both parents .
• They may be dominant or recessive .
• The abnormality merely occur more frequently among relatives than in
general population .
• They play a role that in each generation a recessive characters become
dominant in hierarchy.
• For example club foot ,down syndrome ,Anencephaly and hydrocephalus

7. TYPES OF GENETIC TERATOGENESIS
• There are basically two types of genetic teratogenesis
1. Gene Phene
2. Autophene

8. GENE PHENE
• Several different genes can causes the same terata .
• For example there are more than 20 jeans which affect eye colour in
Drosophila melanogaster.
• The mutant causing the same effect may be either recessive or
dominant .
• In some cases the same mutation maybe either recessive or dominant .
• Ex in mice the fused gene is dominant is mus musculus musculus but
recessive. in mus musculus

9. AUTOPHENE
• Autophene means acting on cells other than those possessing them.
• Not all genetic terta are the result of intrinsic action of gene in the
affected tissue.
• Eg Creeeper mutation in Fowl affected the and the eyes . The embryo
does not survive till hatching . Therefore the creeping gene intrinsically
effect the limb development and it is called autophene but only
indirectly affect the eye development is called Allophene

10. ENVIRONMENTAL TERATOGENESIS
• The environmental factors may be biological or non biological.
1. Teratogenesis due to infection.
• The most dangerous known territogenic organisms is virus of
German measles Rubella contraction of the disease by the mother
during the first month of pregnancy appear to carry about 50% race
of producing congenital abnormality.
2 Teratogenesis due to drugs.
• Drugs like Thalidomide, a sedative may cause amelia (no limbs), and
phocomelia so hands or feet attached directly to the trunk.
• Moreover, aminopetrin (a folic acid antagonist) quinine busulphan
and chlorambusil reported teratogenic in man.
• Pregnant women working in operation theaters (such as
anesthetists, operating nurses) have an increased risk of giving birth
to malformed babies.

11. • 3. Teratogenesis due to Malnutrition .
• Deficiency of various vitamins causes a number of diseases in
man. For example. deficiency of vitamin A-causes night
blindness, of vitamin D leads to abnormal development of bone
and teeth and of vitamin K causes abnormalities in blood
clothing.
• 4. Teratogenesis due to immunization.
• Infant Bond without thyroid gland may have antithyroid
antibodies in their blood and may cross the Placenta and in
using maternal production and the antibodies May return

12. SENSITIVE PERIOD FOR
TERATOGENESIS
• In general very early stages of development not much affected
by teratogen because or regulatory capacity of the embryo.
• Similarly, later stages are also resistant to teratogens.
• The main teratogenic period starts with the formation of germ
layers and upto organogenesis
• . For example, in rat trypan blue and actinomycin D are
maximally teratogenic on 8th and 9th day of gestation, but
ineffective after 10th day and only minimally teratogenic before
6th day of gestation.

13. PHENOCOPIES
• An environmental teratogenesis can cause a normal genotype to produce a
phenotype resembling and allready known mutant
• Phenocopy means mimics of genotype.
• It is not a type of mutation, as it is non-hereditary.
• The term was coined by Richard Goldschmidt in 1935.
Languiser has proposed that a true phenotype fully satisfy two criteria
1. The developmental stages affected by the mutant gene and environmental
teratogens must be same .
2. Modification in genetic background should have similar effect and all the
incidence inexpressibility of both mutant gene and the environmental
teratogens

14. PHENOCOPY
:
• A phenocopy is a non-heritable, environmental phenotype that is
analogous to a genotype-determined phenotype in another
person.
• To put it another way, the phenotype induced by environmental
circumstances resembles the phenotype induced by a gene.
• Vanessa butterflies are an example of phenocopy because their
phenotypic changes depending on the temperature of the
environment. Himalayan rabbits can also do phenocopy.
• When grown in mild circumstances,Himalayan rabbits are white
with black tails, noses, and ears, making them phenotypically
distinct from genetically black rabbits.
• When subjected to cold conditions, Himalayan rabbits develop
black colouring in their coats, making them look like genetically
black rabbits. The Himalayan rabbit has a genetically black

15. • The mechanisms of teratogenesis fall into two broad categories based
on the etiology of the congenital malformations: (a) errors in genetic
programming based on deviations in the genotype of the embryo or the
low probability for error of a normal genotype; and (b) environmental
agents or factors that interact with an embryo during the period of
development (drugs, chemicals, radiation, hyperthermia, infections,
abnormal maternal metabolic states, or mechanical factors).