Teratogenesis.pptx

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 .

1. Teratogenesis By Miss Iram

2. 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 .

3. 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 mal formation . It is a gross structurally deformity present at birth . I ts incidence is about 2.5% in an infant . T he term congenital anomaly is reserved for minor congenital disorder such as deformed f ingers

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

5. Genetic Teratogenesis Abnormal genes may be inherited from one or both parents . T hey may be dominant or recessive . T he abnormality mer e ly occur more frequently among relatives than in general population . T hey play a role that in each generation a recessive characters become dominant in hierarchy . For example club foot , down syndrome ,Anencephaly and hydrocephalus

6. Types of genetic terato Genesis There are basically two types of genetic teratogenesis Gene Phene Autophene

7. Gene Phene Several different genes can causes the same terata . F or example there are more than 20 jeans which affect eye colour in Drosophila melanogaster. T he 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 muscul us muscul us but recessive . in mus muscul us

8. 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

9. Environmental teratogenesis The environmental factors may be biological or non biological. Teratogenesis due to infection. The most dangerous known territogenic organisms is virus of German measles R ubella 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.

10. 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

11. 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.

12. Phenocopies An environmental teratogenesis can cause a normal genotype to produce a phenotype resembling and allready known mutant Pheno copy 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 The developmental stages affected by the mutant gene and environmental teratogens must be same . M odification in genetic background should have similar effect and all the incidence inexpressibility of both mutant gene and the environmental teratogens

13. 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 phenotype as a result of this.

14. 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).