First set of review questions for the third hour exam As for the previous exams, questions marked with a * are more difficult, and not many will be asked. Don't panic if you have difficulty answering them. As before, you are responsible for all the figures and illustrations posted on the course web pages, and also for the linked videos. The exam may include one or more pictures on which you will need to label something, identify something, or explain its significance. Pay particular attention to the narrated videos showing computer simulations of chemotaxis (see links for March 6th). You should understand the difference between spatial and temporal chemotaxis, and be able to explain how they can be simulated using these programs. You might also be asked to draw a graph like those in the second video that would produce a particular effect, or to explain why the spirals are seen in the latter part of this video. You should be able to identify each of the following. For each organ or tissue, explain which germ layer (ectoderm, mesoderm, or endoderm), and which subdivision of that layer, it develops from (for example, neural crest ectoderm or lateral plate mesoderm). You should also be able to sketch and describe whatever folding or fusions of cell sheets occur in the formation of each. Neural crest, neural tube, somatic ectoderm, epidermis, hair, feathers, scales of reptiles {Note: reptile scales develop from epidermis; but fish scales are mesodermal!} pigment cells, Schwann cells, lobes of the brain, lens of the eye, optic cup, choroid fissure, pigmented retina, neural retina, ganglion cells, optic nerve, optic chiasm, optic tectum, retino-tectal projection, neural projections, ephrin protein, spinal cord, spinal nerves, sensory nerves, post-ganglionic autonomic nerves {from the neural crest; what else!}, placodes, olfactory nerve, nostril, palatal shelves, neuromast cells, semicircular canals, otoliths, cochlea, lateral line, ameloblasts, enamel, dentine, teeth, pharyngeal pouches, gill slits, eustachian tube, tonsils, parathyroid glands, thymus organ, salivary glands, thyroid gland, lungs, alveoli, pancreas, liver, cloaca, bladder, rectum, cartilage, bone, notochord, paraxial mesoderm, somites, dermatome, myotome, sclerotome, intermediate mesoderm, pronephros, pronephric duct = Wolffian duct = Vas deferens = mesonephric duct, mesonephros, metanephros, ureter, lateral plate mesoderm, genital ridges, ovary, oviduct, Müllerian duct, testis, sperm duct, Fallopian tube, uterus, coelomic cavity, heart, vena cava, ductus arteriosus, inter-ventricular septum, situs inversus, Remember that in the facial area, neural crest cells form all tissues that develop from mesoderm in other parts of the body, including the skeleton. Which organs are formed by infolding placodes of somatic ectoderm? nose, lens, inner ear Which are formed from pharyngeal pouches in the neck? Eustachian tube, tonsils, thyroid, parathyroid gland Name as many differentiated cells as you can that develop from neural crest cells. Why do reptile, bird and mammal embryos develop three pairs of kidneys? (Don't worry about fish and amphibian kidneys.) You should be able to draw a diagram of the pronephros, pronephric duct, mesonephros, metanephros, and ureter. What are some other names for the Wolffian duct? pronephric duct, mesonephric duct, vas deferens The sperm ducts of male mammals, reptiles and birds were used for what purpose during embryonic development, when no sperm were being produced yet? What do the oviducts develop from? outfoldings of the coelomic wall, = inner layer of lateral plate mesoderm Does the future oviduct ever serve as a urine duct? Hint: no The lateral plate mesoderm splits into two layers, with what between them? the coelom, fluid Where do the testes originate in development of mammals, and what happens to them during development? What is another example of organ migration in mammals (in addition to the testes)? kidney moves toward the anterior Contrast the internal histology of the testes (seminiferous tubules) and the ovaries (follicles). Be able to describe or sketch them. Guess why many animals develop two uteruses. By what experimental disturbance could you cause two uteruses to develop in a species that normally forms only one? Human embryos form two oviducts but (normally) only one uterus. Why and how? How can you cause a vertebrate embryo to develop two hearts? In the development of the heart, do we first form a one-chambered embryonic heart, then replace it with a two chambered fetal heart, which we use to pump blood while we construct the 4-chambered heart that we will use after birth and for the rest of our life? (Hint: no) But what do we do instead? In what way is that imaginary sequence of hearts analogous to what actually happens in the embryonic development of kidneys? A serious birth defect that sometimes occurs is that a hole connects the right and left ventricles of the heart. To what other birth defects in other organs is this analogous? Hint: It isn't called "cardia bifida" but that might have been chosen as a name. (Does it result from something having cut or cleaved a hole through the septum between the ventricles?) Hint: no.) Until birth, blood flow and oxygenation of blood is not abnormal in babies with holes connecting their two ventricles: why not? Please explain why oxygenation of blood then suddenly become very abnormal in these babies, at the time of birth (but worked OK before birth)? Do mammal embryos ever develop a hole connecting their right and left atria? (Trick question!) Yes, a hole always forms - and what shape is this window-like hole? Oval shape of foramen ovale List as many examples as you can in which the boundary between two different tissues or differentiated cell types develops at the location of a sharp fold in an epithelial sheet of cells. (Dozens of examples occur). Can you list examples in which anatomical boundaries do NOT begin as folds? How might the developing Wolffian duct tips be guided toward the cloaca? Maybe by chemotaxis? Maybe by haptotaxis (i.e. an adhesion gradient)? Can you devise experiments to distinguish between alternative guidance mechanisms? * If a diffusible chemical caused localized increases in either the adhesiveness or the contractile strength of parts of crawling tissue cells (i.e. some component cells of our body, or of an embryo) then would concentration gradients of that chemical cause cells to orient their locomotion up concentration gradients of this diffusible chemical? Hint: yes. Would this be chemotaxis? or haptotaxis? or both? Which kind of chemotaxis? Stomodeum is to the palate as cloaca is to the tissue that separates the bladder from what? from the rectum Cleft palate is to the stomodeum as septal defects are to what? the heart Please explain the relationships in both these analogies. Which organs develop from invaginations in the stomodeal ectodermal epithelium? teeth, pituitary gland, some of the salivary glands, thyroid What is a placode? Where do they develop? Sketch a cross section of a placode in the process of forming. The lenses of the eyes develop from what, in what part of which germ layer? somatic ectoderm How does the inner bone-like dentine layers of teeth form? Neural crest cells aggregate on the inner surface of sheets of ameloblasts. Why are alligators able to continue replacing their teeth all during their life? Because a strip of invaginated stomodeal epithelium continues to exist and bud off vesicles of cells that differentiate into ameloblasts. What embryological difference causes birds not to form teeth? Inductive signals are no longer sent from their neural crest cells to induce stomodeal ectoderm to differentiate into ameloblasts. What is the evidence for that explanation? Kollar & Fisher grafted mouse neural crest cells to locations next to stomodeal ectoderm cells from chicken embryos, and teeth developed. What were some other possible genetic changes that could have resulted in evolutionary loss of teeth? Loss or mutation of receptors of the inductive signals that stimulate either ameloblast or odontoblast development. Mutations in genes needed for synthesis of either enamel or dentine. Several other possibilities, that you ought to be able to invent. Imagine the possibility that some of the grafted mouse neural cells changed their differentiated state and became ameloblasts: Explain why the Kollar and Fisher experiment could thave led to erroneous conclusions. What if some mouse stomodeal epithelial cells had accidentally been included among the grafted mouse neural crest cells; how could that have resulted in erroneous results? Suggest how to test for the possibility of such errors of interpretation. For example, what if fossil teeth from prehistoric birds had enamel which differed in some clear way from mammal enamel? What if a green fluorescent marker had been inserted into mouse genes for making enamel? Then, how could you use this to reduce the possibility of misinterpreting the Kollar and Fisher experiment?