Neurulation refers to the early formation of the nervous system in vertebrate embryos.  It begins when the notochord, a rodlike mesodermal structure, induces neural tube and neural crest cell formation in a different germ layer called the ectoderm.Neural tube defects (NTDs) arise from abnormalities in the development of the neural tube and can range from mild to severe, depending on which portion of the tube is affected.  Spina bifida, a form of NTD, is divided into three categories.  The most serious subclassification of spina bifida is myelomeningocele, which occurs when the lower spine fails to close and leaves the spinal cord and nerve roots in the lower back damaged and exposed.NTDs are thought to be caused in part by folate deficiency.  Folate plays a critical role in normal cell division and growth as it is a necessary coenzyme for DNA synthesis and methylation.  Mutations in several genes involved in folate metabolism have been associated with an increased risk for NTDs.  It has been hypothesized that folate decreases NTD risk by ameliorating oxidative stress, thereby reducing damage to developing cells in the embryo.  Certain maternal conditions, such as high blood glucose, increase the risk of NTD development by enhancing embryonic oxidative stress during crucial developmental periods.A study was conducted to examine how supplementation with folic acid, the dietary form of folate, affected pregnant women who were identified with preexisting diabetes, pregestational obesity (another risk factor for NTD), or no preexisting conditions (control group).  Higher folic acid intake decreased the incidence of embryonic NTDs among pregnant women with diabetes but no significant effect was found for pregnant women who were obese.Adapted from Parker, S.E., Yazdy, M.M., Tinker, S.C., Mitchell, A.A., & Werler, M.M. (2013). The impact of folic acid intake on the association among diabetes mellitus, obesity, and spina bifida. American journal of obstetrics and gynecology, 209(3), 239.e1–239.e2398. Question 27Undifferentiated gastrula cells presumed to give rise to neural tissue were transplanted from a donor frog embryo into a host frog embryo.  The cells were transplanted among undifferentiated host gastrula cells presumed to give rise to epidermal tissue.  Both host and donor embryos were allowed to develop following the transplant and gave rise to two normal embryos.  What was the purpose of this experiment?A.To determine which cells in the gastrula ultimately give rise to epidermal tissueB.To determine if cell specialization is influenced by communication between cellsC.To determine how developmental fates of cells are determined during blastula formationD.To determine whether cell differentiation could be reversed based on embryonic location