Zone of polarizing activity (zpa), Biology

Assignment Help:

Zone of Polarizing Activity (ZPA)

The A-P axis is the 1st axis to be fixed in the presumptive limb mesoderm at a very early stage. On the basis of results of a series of current experiments on chick embryos it has been recommended that determination of the anterior-posterior pattern of wing parts is apparently within the control of a small block of mesodermal cells located at the posterior junction of the wing bud along with the body wall. This mesoderm has been termed as the Zone of Polarizing Activity (ZPA). The usual chick wing has three digits numbered II, III and IV in this anterio- posterior order. In stage 18 or little older embryos an extra ZPA was transplanted within the ectoderm on the anterior side of the bud near or in contact with the AER. This resulted in the creation of a duplicate set of digits in reverse order on the anterior side so the digital formula anterio-posteriorly turns IV, II, II- II, III, IV.

The second set was a mirror image of the original. The normal polarity was kept even in this set as the usually the most posterior digit IV was still nearest to the transplanted ZPA. It was recommended that ZPA secretes some type of substance, a morphogen, whose diffusion creates a gradient of decreasing concentrations along with the A-P axis. The digit IV may be formed in response to the highest concentration and digits III and II in response to in succession decreasing levels of this morphogen. A second such gradient would be established in reverse direction by the morphogen produced by the ZPA transplanted on the anterior side and hence the second set of digits in mirror image of the original set the above suggested role of ZPA is not generally accepted by most biologists. Identical additional set of digits in chick wing is induced by transplantation of mesoderm from another body regions, several different tissues, transplantation of an additional AER and as well by applying retinoic acid (a derivative of Vitamin A) to the anterior side of the bud. Furthermore, removal of ZPA from the posterior side of the bud does not prevent the creation of the normal set of digits while in an experimental situation ZPA does produce a polarizing effect, this role of ZPA in the normal development whereas it is in its usual posterior position in the wing bud is seriously doubled.


Related Discussions:- Zone of polarizing activity (zpa)

How much of solution to add 10ng of dna in a reaction, I dissolve 4µg of DN...

I dissolve 4µg of DNA in 1mL of water. How much of this solution would I need in order to add 10ng of DNA in a reaction?

Terms of incubation time and the generation time, If the generation time (t...

If the generation time (t) is the incubation time (t) per generation (G), or t = t/G, rewrite the formula you derived in question 2 for bacterial population growth in terms of incu

What is waterston shunt in palliative operations, What is Waterston Shunt i...

What is Waterston Shunt in palliative operations? In this, direct anastomosis between the posterior aspect of ascending aorta and anterior aspect right pulmonary artery is done

How is retaining structure used, How is retaining structure used? A ret...

How is retaining structure used? A retaining wall helps in maintaining the surface of the ground at different elevations on either side of the structure. If the retaining wall

Explain oxidative phosphorylation, Explain Oxidative phosphorylation ...

Explain Oxidative phosphorylation Oxidative phosphorylation  : Synthesis of ATP  from ADP  and  Pi  during the passage of electrons in the respiratory chain.

Are there aquatic and flying mammals, Q. Are there aquatic and flying mamma...

Q. Are there aquatic and flying mammals? Sirenians (dugongs, manatees) and Cetaceans (whales, dolphins) are aquatic mammals Chiropterans (bats) are flying mammals.

Describe gastrovascular cavity in detail, Describe Gastrovascular cavity in...

Describe Gastrovascular cavity in detail? The name given to the internal cavity of cnidarians. A blind-ended (incomplete) gut with only one opening. Food is to be digested and

Why greenhouse gases lead to global warming, Explain briefly why 'greenhous...

Explain briefly why 'greenhouse' gases lead to global warming. The greenhouse gases do not interfere with the short-wave radiation reaching the Earth from the sun but take up t

Do bacteria cells have a nucleus, Q. Do bacteria cells have a nucleus? ...

Q. Do bacteria cells have a nucleus? In bacteria the genetic material is dispersed in the cytosol and there is no inner membrane that delimits a nucleus.

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd