Embryonic Induction

Embryonic Induction
Definition
An embryonic tissue influences upon the other embryonic tissue through transmitted some chemical stimulus. This phenomena is called Embryonic Induction.
Experiment Or Mechanism of Embryonic Induction
Introduction
Hans Spemann, a classical embryologist, who got Nobel Prize in 1935 performed an experiment of embryonic induction in 1924.
Experiment 1
Han Spemann separated the tissue frm presumptive nervous system present above the nerve cord and transplanted into the belly region of the embryo.
Conclusion
He observed that these tissues of nervous system failed to develop at ectopic site.
Experiment 2
In another experiment, they separate the presumptive notochord tissue and then transplanted into presumptive belly ectoderm.
Conclusion
Nervous tissues started germination and they developed into neural tissues.
Result
From these experiments they concluded that an embryonic tissue influence upon the other embryonic tissue through transmitting some chemical stimulus the primary organizer. They help in embryonic induction.
Regeneration
Definition
The ability to regain or recover the lost or injured part of the body is called Regeneration.
Regeneration in Invertebrates
Regeneration is very common in most of the invertebrates, such as Sponges, Coelentrates, Pranarians, Annelids, Nematodes, Molluscans, Arthropods and Echinoderms.
In hydra a small piece of the body can be changed into a complete animal. In earthworm and planaria when the body divides into two or more fragments each fragment can develop into a new animal.
Regeneration in Vertebrates
In vertebrates many groups have the ability of regeneration for example Salamander and Lizard regenerate their limb and tail. Birds and Mammals have very poor regenerative ability. In human the skin has this capability.
Abnormal Development
Deviation in the normal structure and functions of an organisms occur under favourable conditions during embryological development are called abnormal development. The study of such abnormalities is called Teratology.
Causes
The main reasons for the abnormal development are as follows
Mutation
Change in number of chromosome
Ultra voiled rays
Strong medicines
Abnormal functioning of certain glands.
Following are the some abnormal conditions in human
i. Microcephaly
In this condition, individual with very small skull are born.
ii. Clef Lip and Palate
Upper lip has a cleft and there is a gap between the palate.
iii. Polydactyle
Number of digits exceeds normal number.
iv. Dextrocardia
Heart towards the right side of the chest.
v. Sickle Cell Anemia
R.B.C become sickle shaped due to abnormality.
vi. Turner’s Syndrome
Female sexual defect in which there is one less sex chromosome.
vii. Klinefelter’s Syndrome
Male sexual defect in which one more sex chromosome is present.
viii. Down’s Syndrome
Mental and physical retardation
ix. Haemophilia
Decreased ability of the blood to clot.
x. Thalassemia
Formation of fragile (weak) R.B.C which break down and cause haemolytic anemia.
Role of Cytoplasm in Development
Cytoplasm is also important of embryo. To show the importance of cytoplasm experiment was performed on frog’s embryo.
Experiment
The unfertilized egg of frog has an upper pigmented half and a lower non-pigmented yolk half. After fertilization a third region called Gray Crescent appears just opposite to the point of entry of the sperm. As a result of first cleavage the embryo divides into two daughter cells each receiving exact half of the Gray Crescent. When the two daughter cells were separated each grow into normal tad pole larva. In experiment Has Spermann separated the two cell in such a way that one cell received all the Gray Crescent and the other cell got none. It was seen that only that ceil developed into tadpole which had the cytoplasm from the Gray Crescent while the other turned into undifferentiated mass of cells while later died.
Conclusion
It can be concluded that although both cells had similar genes, cytoplasm of both was different. This shows that cytoplasm has some regulatory effect on the expression of genes.
Role of Nuclues in Development
Nucleus is a part of cell which acts like a brain. It also play an important role in reproduction. The role of nucleus in regulating the activities of cytoplasm was studied in a unicellular alga.
Experimental Material
Hamerling used alga plant named Acetabularia, which has a long stalk and at the tip a cap like structure. The cap is of two types one is umbrella shaped and another is irregular-shaped. The nucleus is present in the lower region of the plant.
Experiment
When caps of both types were removed each plant again produced cap of its own type. When cap and stalk were grafted on the bases of the plant of other types. In this experiment it was observed that each type produced the cap of its own shape inspite of having separate-stalks.
Conclusion
Hence it is concluded that the development of cap was regulated by the nucleus rather than the cytoplasm.