You are studying the development of a poorly-understood species at the 8-cell stage. You use a laser to zap away a certain one of the eight cells, and discover that part of the gut is missing once the embryos finish development. Your colleague, who is working on a different species, uses the laser to blast away one of the cells in her embryos, zapping each of the possible cells in a set of eight experiments. However, when the embryos finish development, every one is perfectly normal! What can you conclude about the two species?
A. The first species has regulative development, the second has non-regulative development.
B. The first species has non-regulative development, the second has regulative development.
C. Both species have regulative development.
D. Both species have non-regulative development.
Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?
Gather Content
What do you already know about cleavage and developmental pathways? What other information is related to the question?
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
B. The first species has non-regulative development, the second has regulative development.
Clarify Question
What is the key concept addressed by the question?
· The concept addressed here is the nature of the developmental path of two different species.
What type of thinking is required?
· Evaluate level:
o This question is asking you to weigh and judge, or evaluate, the differing developmental pathways of two species.
Gather Content
What do you already know about cleavage and developmental pathways? What other information is related to the question?
· Cleavage stage embryos often look like a simple ball or disc of similar cells.
· In many animals, this appearance is misleading; for example, the unequal segregation of cytoplasmic determinants into specific blastomeres of tunicate embryos commits those cells to different developmental paths. The experimental destruction or removal of these committed cells results in embryos deficient in the tissues that would have developed from those cells.
· In contrast, mammals exhibit highly regulative development, in which early blastomeres do not appear to be committed to a particular fate. For example, if a blastomere is removed from an early eightcell stage human embryo, the remaining seven cells of the embryo will “regulate” and develop into a complete individual if implanted into the uterus of a woman.
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
· The first species has non-regulative development, because the loss of one of its blastomeres causes the loss of a structure in the developing embryo.
· The second species has regulative development, because any of the blastomeres can develop into a complete embryo.
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
· Evaluate level:
o Answering this question correctly depended on your ability to weigh and judge, or evaluate, regulative and non-regulative development. If you got an incorrect answer, did you remember that non-regulative development involves blastomeres that are predetermined to be certain tissues, or blastomeres in a species that exhibits non-regulative development can become complete embryos? Did you have trouble weighing the merits of regulative development relative to non-regulative development to determine the correct answer?
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