The H3.H4 tetramers and H2A.H2B dimers each interact with a particular region of the DNA within the nucleosome. Which of the following statement is CORRECT regarding the characteristic binding of histones with the DNA?

I. Of the 147 bp of DNA included in the structure, the histone-fold regions of the H2A.H2B dimer interact with the central 60 bp.

II. Histone H3.H4 tetramers occupy a key position in the nucleosome by binding the middle and both ends of the DNA.

III. The amino-terminal region of H4 most proximal to the histone-fold region forms a fourth alpha helix that interacts with the final 13 bp at each end of the bound DNA.

IV. The H3.H4 tetramer associate with approximately 30 bp of DNA on either side of the central 60 bp of DNA bound by H2A.H2B dimer.

V. The two H2A.H2B dimers form the bottom part of the histone octamer located across the disc from the DNA ends.

#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