Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous. The dicynodonts had two large tusks, extending down from their upper jaws; the tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record, these pig-sized organisms were the most common mammal-like reptiles of the Permian. Anatomically, what was true of Lystrosaurus?

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#Question id: 14834

#Unit 5. Developmental Biology

Process by which a spatial and temporal pattern of cell activities is organized within the embryo so that a well-ordered structure develops:

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#Question id: 14835

#Unit 5. Developmental Biology

There are three main ways in which inducing signals may be passed between cells EXCEPT

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#Question id: 14836

#Unit 5. Developmental Biology

In the case of the French flag model. we assume a source of morphogen at one end and a sink at the other and that the concentrations of morphogen at both ends are kept constant but are different from each other. If the cells can respond to threshold concentrations of the morphogen, Thresholds can represent the

a. amount of morphogen that must bind to receptors to activate an intracellular signaling system. 

b. concentrations of transcription factors required to activate particular genes.

c. concentration at any point effectively provides positional information.

d. amount of morphogen that must bind to receptors to inactivate an extracellular signaling system.

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#Question id: 14837

#Unit 5. Developmental Biology

Each of the three major strategies of cell specification summarized in TABLE  offers a different way of providing each embryonic cell with a set of determinants (often transcription factors) that will activate specific genes and cause the cell to differentiate into a particular cell type:

Choose right combinations;

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#Question id: 14838

#Unit 5. Developmental Biology

Sequence of amphibian lens induction postulated by experiments on embryos of the frog Xenopus laevis ; EXCEPT

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#Question id: 14839

#Unit 5. Developmental Biology

Given are certain facts which define ‘specification’ of a developing embryo.

 A. At the specification stage, commitment to cell identity is labile.

 B. At the specification stage, cell is capable of differentiating autonomously.

 C. The cell “knows” very early what it is to become without interacting with other cells.

 D. A phase where inductive signals trigger cell to determines their fate.

 Which of the above statements best define specification?