CSIR NET 2022 | Life Science: Developmental Biology |7 November

The following demonstrates proposed functions of different genes which determine the decision to become either trophoblast or inner cell mass (ICM) blastomere during early mammalian development:

Based on the above figure, which oneof the following assumptions is correct?

The anterior-posterior compartment of each segment of Drosophila is defined by wingless and engrailed genes. The following statements are given towards explaining their regulation:

i. Wingless is a secretory factor

ii. Engrailed is a secretory factor and forms a long-range concentration gradient

iii. Engrailed regulates Wingless through Hedgehog which forms a short-range concentration gradient

iv. β-catenin homologue is the signaling molecule upstream of Engrailed, which gets cleaved by GSK3 homologue

v. Cubitus interruptus is an intracellular signaling molecule in the Engrailed expressing cells.

Which one of the following options has all the correct statements towards the regulation of anterior-posterior compartment of segments?

Following statements are being made regarding specification/ determination during animal development:

i. During the course of commitment, the cell may not appear different from its nearest or most distant neighbors in the embryo and show no visible signs of differentiation; but its developmental fate is restricted.

ii. At the stage of specification, cell commitment is not labile.

iii. A cell or tissue is determined when it is capable of differentiating autonomously even when placed into another region of the embryo, or a cluster of differently specified cells in a petridish.

iv. Cytoskeletal arrangements maintain positioning of nuclei in the syncytium, which enables specification of these nuclei by opposing morphogen gradients namely Bicoid and Caudal in Drosophila.

v. Capacity for “mosaic” development allows cells to acquire different functions as a result of interactions with neighboring cells.

Which of the above statements are correct?

A “morphogen” can determine the fate of a cell by its concentration. Given below are some statements on the experiment performed to study the gradient-dependent effect of the morphogen, activin on cell fate by placing activin (4 nm) – secreting beads on unspecified cells from an early Xenopus embryo:

i. Beads without activin did not elicit expression of either Xbra or goosecoid genes.

ii. Cells nearest to the beads getting highest concentration of activin induced goosecoid gene whose product is a transcription factor, specifies the frog’s dorsal-most structures.

iii. Cells nearest to the beads getting highest concentration of activin induced Xbra gene whose product is a transcription factor, specifies the frog’s dorsal-most structures.

iv. Cells farthest from the beads getting negligible activin activate Xbra gene and become blood vessels and heart.

v. Cells farthest from the beads getting negligible activin, activated neither Xbra nor goosecoid and the ‘default’ gene expression instructed the cells to become blood vessels and heart.

Which of the above observations and conclusions drawn are correct?

A specialized area of teratogenesis involves the mis regulation of the endocrine system. Which one of the following statements regarding endocrine disruptors is true?