The diagram below represents a hypothetical operon in the bacterium E. coli.  The operon consists of two structural genes (A and B), which code for the enzymes A-ase and B-ase, respectively, and also includes P (promoter) and O (operator) regions as shown.

 When a certain compound (X) is added to the growth medium of E. coli, the separate enzymes A-ase and B-ase are both synthesized at a 50-fold higher rate than in the absence of X.  (X has a molecular weight of about 200.)  Which of the following statements is true of the operon decribed above?

#Question id: 7181

#Unit 5. Developmental Biology

Following graph represents Inhibition of L1-mediated cell adhesion by alcohol.

If L1 is mutate, which of the following graph is correct?

#Question id: 7182

#Unit 5. Developmental Biology

Suppose a flower had normal expression of genes A and C and expression of gene B in all four whorls. Based on the ABC hypothesis, what would be the structure of that flower, starting at the outermost whorl?

#Question id: 7183

#Unit 5. Developmental Biology

Following graphs (A and B) represents establishment of a maternal gradient in Hunchback protein.

which of the following statements are correct according to graphs?

#Question id: 7184

#Unit 5. Developmental Biology

The figure above represents a late zebrafish gastrula. The following concepts may be proposed during further development of the embryo.

A. The concentration of FGF decreases from the yolk towards the epidermis, along with the increase of BMP activity from the dorsal to the ventral axis.

B. Increase in FGF activity in the epidermis with concomitant decrease in BMP activity towards the ventral axis.

C. Neural induction in zebrafish is independent of the organizer and depends on activation of BMP signalling.

D. In comparison, both Xenopus and chick embryos require activation of FGF for neural induction to occur in addition to BMP inhibition.

Which of the above statements are incorrect?

#Question id: 7185

#Unit 5. Developmental Biology

Following statements are regarding to establishing the three separate cell lineages in the mouse blastocyst.

A. The first two cell types to be specified are the inner cell mass and the trophectoderm. This involves progressive restriction of expression of the genes that code for transcription factors Oct4 and Cdx2.

B. At the eight-cell stage, all the cells express both genes at low levels, but by the late morula/early blastocyst stage, Cdx2 expression has increased in, and eventually becomes restricted to, the cells on the outside of the embryo, and these will form trophectoderm. Oct4

expression becomes restricted to the inner cell mass cells at early blastula stage.

C. Within the inner cell mass, two separate cell types arise: the epiblast cells, from which the embryo will develop; and the primitive endoderm, which will form extra-embryonic structures. This involves a progressive restriction of expression of the genes for the transcription factors Nanog and Gata6.

D. At the early blastula stage, some of the inner cell mass cells apparently at random start to express higher levels of Nanog, whereas the other cells express higher levels of Gata6.

E. By the late blastula, the cells expressing the two different transcription factors have sorted out within the inner cell mass so that cells expressing high levels of Nanog form an outer epithelial layer of primitive endoderm enclosing the epiblast cells expressing high levels of Gata6.

Which of the following statements are correct?

#Question id: 7186

#Unit 5. Developmental Biology

In dictyostelium stalk and spore cell maturation depends on cAMP level. Which of the following statement is incorrect regarding to this process?