Following are certain statements regarding

morphogen gradients and cell specification.

A. Morphogens are always transcription factors

B. Morphogens can be paracrine factors that are produced in one group of cells and travel to another population of cells

C. When the concentration of a morphogen drops below a certain threshold, cells stop differentiating and never get determined to another fate

D. Morphogen gradients are involved in conditional specification

Which combination of the above statements is true?

#Question id: 5138

#Unit 5. Developmental Biology

When presomitic mesoderm (PSM) that would ordinarily form thoracic somites is transplanted into a region in a younger embryo (caudal to the first somite) that would ordinarily give rise to cervical (neck) somites, the grafted mesoderm differentiates according to its original position and forms ribs in the neck. This phenomena is called as:

#Question id: 5139

#Unit 5. Developmental Biology

There are two broad categories of receptors that activate tyrosine kinases: (1) those in which the tyrosine kinase enzyme is an intrinsic part of the receptor’s polypeptide chain, called the_________ and (2) those, in which the receptor and kinase are separate polypeptides, encoded by different genes, yet are bound tightly together, called the __________.

#Question id: 5140

#Unit 5. Developmental Biology

Following statements regarding to the Ectodermal competence and the ability to respond to the optic vesicle inducer in Xenopus.

A. The optic vesicle is able to induce lens formation in the posterior portion of the ectoderm but not in the anterior portion.

B. If the optic vesicle is removed, the surface ectoderm forms either an abnormal lens or no lens at all.

C. Only head ectoderm is competent to respond to the signals from the optic vesicle by producing a lens.

D. The head ectoderm appears to secrete two paracrine factors BMP 4 and FGF8, which involves in the activation of lens-specific genes such as crystallin.

Which of the following combination is incorrect?

#Question id: 5141

#Unit 5. Developmental Biology

Which of the following statement not describe the concept of morphogenetic gradient?

#Question id: 5142

#Unit 5. Developmental Biology

The D set of blastomeres is the “organizer” of snail embryos. Experiments have demonstrated that the non-diffusible polar lobe [cortical] cytoplasm that is localized to the D blastomere is extremely important in normal molluscan development.  Which of the following is incorrect?

#Question id: 5143

#Unit 5. Developmental Biology

Select the correct sequence of events in photoreceptor induction in drosophila.

A. Morphogenetic furrows moves across eye disc

B. Eyeless gene expression

C. R8 photoreceptor cells develop

D. R7 photoreceptor cells develop