17. You learned that exposure to the toxin cyclopamine from the corn lily cause

Question

17. You learned that exposure to the toxin cyclopamine from the corn lily cause sheep to develop with only one eye. Which of the following is true of cyclopamine rhythms and affects the 24 hour cycle of the sheep. A) it interferes with the circadian B) it inactivates the HOXA1 gene causing it not to be expressed. inducer of cell fate determination C) it acts as an D) it interferes with an inducer that is part of the hedgehog signaling pathway. 18. Positive feedback differs from negative feedback in that A) the positive feedback effector responses are in the same direction as the initiating stimulus rather than opposite B) positive feedback benefits the organism, whereas negative feedback is detrimental C) the effector's response increases some parameter (such as body temperature), whereas in negative feedback it can only decrease the parameter D) positive feedback systems have only effectors, whereas negative feedback systems have only receptors 19. (1 pt The body's automatic tendency to maintain a constant and optimal internal environment is termed A) static equilibrium B) homeostasis. C) homeopathy D) physiological chance 20. In an NPR radio clip and in lecture you learned about the consequences of mutating the human HOXA1 gene. Which of the following is FALSE regarding the human HOXA1 gene? A) mutations disrupt brainstem, inner ear, cardiovascular and cognitive development B) HOXA1 is expressed in the human head C) mutations cause unusual eye movements D) mutations are common in human populations 21. How did Nobel Laureate Edward Lewis discover Hox gones in the fruit fly Drosophila melanogaster? A) by screening for mutations that affect the embryos dorsal-ventral pattern by looking in the genome sequence for genes encoding transcription factors C) by screening for mutations that cause body parts to appear in unusual D) by searching for homeobox sequences in the genome 22. (1 pt) You have a cube of modeling clay in your hands. How can you change the shape to DECREASE its surface area relative to its volume? A) Round the clay up into a sphere. B) Pinch the edges of the cube into small folds. C) Stretch the cube into a long, shoebox shape. D) Flatten the cube into a pancake shape 23. In the context of development and patterning. transplantation experiments have demonstrated that patterning does not depend on unequal distribution throughout the embryo of extracellular ligands B) the transplanted tssue can generate signals that affect the cell fate of the cells receiving them C) patterning can only result from the active induction of particular cell fates, not repression of default cell fates patterning genes are highly conserved at the DNA sequence level 24. Embryonic induction, the influence of one group of cells on another group of cells, plays a critical in embryonic development. In 1924. Hans Spemann and Hilde Mangold transplanted a piece of that ventral side of another of the and tube the dorsal lip of an embryo to the embryo. induction occurred, which of the following observations justifies the claim of embryonic induction? induced the formation of a second notochord and neural tube on the ventral side of the A) the transplanted tissue By the transplanted tissue inhibited normal cell division on the dorsal side of the recipient embryo that ead to the transplanted tissue multiple develop on the ventral side of the recipient embryo D) transplanted had no effect either the the embryo it continued Page 3 of 22

Explanation / Answer

17. A

18. A. the positive feedback's effector responses are in the same direction as the initiating stimulus rather than opposite to it.

19. B. homeostasis

20. C

21. D.

22. A.

Explanation:-the sphere is the shape with minimal surface area among all bodies of the same volume, by the isoperimetric inequality.

23. C.

24. A.

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