Question 1

In the famous Spemann-Mangold experiment,what detail was crucial to understanding the result?

Accepted Answer

The use of genetically different donor and host frogs allowed researchers to distinguish between the cells of the donor and the host, demonstrating that the transplanted dorsal lip cells could induce the formation of a second embryonic axis.

Question 2

What is critical to the development of neural crest cell derivatives?

Accepted Answer

Regulation of N-cadherin is critical for the development of neural crest cell derivatives because it plays a key role in the process of epithelial-to-mesenchymal transition (EMT), which is essential for the migration of neural crest cells to their various target locations in the embryo.

Question 3

What human organ is formed from two genetically-different tissues?

Accepted Answer

The placenta is formed from both fetal tissues (derived from the trophectoderm) and maternal tissues (derived from the endometrium). The fetal portion contains cells of the chorion, while the maternal portion contains cells of the decidua. These tissues have different genetic origins, with the fetal tissue containing DNA from the developing embryo and the maternal tissue containing DNA from the mother.

Question 4

400 micrograms a day of folic acid are recommended for all women of child-bearing age.Folic acid helps prevent neural tube defects in the first weeks of pregnancy,before most women even realize they are pregnant (and almost half of pregnancies in the U.S.are unintended).Knowing that folic acid promotes proper neural tube closure,which disease can be prevented by this supplement?

Accepted Answer

Folic acid helps prevent neural tube defects in the first few weeks of pregnancy, which includes spina bifida.

Question 5

What prevents menstruation from occurring in the 10^th week when the corpus luteum regresses?

Accepted Answer

The placenta takes over secretion of estradiol and progesterone, which maintains the endometrial lining and prevents menstruation from occurring in the 10th week when the corpus luteum regresses. The follicle does not secrete hCG or take over secretion of estradiol and progesterone. The cervix does not secrete oxytocin or prostaglandins that affect menstruation.

Question 6

In a normal mammalian birth,how does the body guarantee that birth proceeds to completion?

Accepted Answer

During mammalian birth, the body guarantees that birth proceeds to completion via positive feedback. The stretching of the uterus by the descending fetus induces release of oxytocin from the posterior pituitary, which causes even stronger uterine contractions. This positive feedback loop continues until the baby is born.

Question 7

What basic developmental challenge is solved by the organizer?

Accepted Answer

The organizer plays a crucial role in early embryonic development by inducing the formation of the dorsal-ventral axis from a spherical ball of cells, guiding the spatial organization necessary for proper development.

Question 8

In blind cave fish,eyes do not form.However,transplantation of the lens from a closely-related aboveground fish into the optic cup of the cave fish induces eye development.What does this suggest about the loss of vision in the cave fish?

Accepted Answer

The transplantation experiment suggests that the lens from the aboveground fish contains a necessary signal for eye development that the cave fish lens lacks. This indicates that the process of secondary induction (where one tissue influences the development of another) is failing in the cave fish due to the absence of a critical signal from the lens, not because the optic cup cannot receive the signal.

Question 9

The snakes include some rather short and some incredibly long species,with a variation from about 100 to over 300 vertebrae.What developmental mechanism is the best candidate for changing the number of vertebrae in evolution?

Accepted Answer

The somitogenesis clock is responsible for the segmentation of vertebrate embryos, which leads to the formation of vertebrae. Changes in this clock could result in changes in the number of vertebrae in evolution.

Quiz 52: Animal Development