GRE Subject Test: Biology : Animal Biology
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Example Questions
Example Question #2 : Understanding Organogenesis
The inner cell mass (or embryoblast) of the blastocyst gives rise to all of the following layers except __________.
the primitive endoderm
the trophoblast
the epiblast
the mesoderm
the trophoblast
The blastula, or blastocyst, is made up of blastomere cells and a fluid-filled cavity called the blastocoel.
There are two regions of the blastocyst: the inner cell mass and the trophoblast. The inner cell mass gives rise to the primitive endoderm and the epiblast, which later gives rise to the three germ layers during gastrulation. The trophoblast is the layer of cells forming the outer ring of the blastocyst. It secretes factors to make the blastocoel and is kept separate from the inner cell mass. All fetal structures eventually develop from the inner cell mass, while the trophoblast helps maintain the fetal environment and placenta.
Example Question #1 : Developmental Physiology
During embryogenesis, the process in which a committed cell develops distinctive functions and characteristics is known as __________.
specification
differentiation
induction
determination
differentiation
Once a committed cell begins to develop specialized functions, it is known as differentiation. Before a cell differentiates, it makes a commitment to a certain cell type, first by specification, which is reversible, and then by determination, which is irreversible. Once a cell is committed to a cell type, it undergoes differentiation to develop specific cell characteristics.
Induction is a process in which cells induce adjacent cells to commit to a certain cell type.
Example Question #4 : Animal Development
What gene expression regulatory proteins control cell type specific genes and define cell identities that are indispensible in differentiation and development?
Mediator
All of these answers
Master transcription factors
Pioneering transcription factors
Chromatin remodelers
Master transcription factors
The correct answer is master transcription factors. The type of master transcription factor expressed in a cell depends on the ultimate cell type it will become. Master transcription factors have higher affinity for cell identity genes. Each cell type has a different profile of master transcription factors that are reliably expressed. Mediator facilitates binding and recuitment of many transcription factors. Chromatin remodelers change the epigenetic state in a cell, and pioneering transcription factors are the first factors to bind DNA, even in heterochromatin regions.
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