What if such abnormal polar bodies developed as parts of the body?Ħ) Why decide differentiated cell type by such active rearrangements as invagination, ingression and other "morphogenetic movements"? either one or both polar bodies would be much bigger, even as big as a quarter or half the oocyte). It is haploid and if it fuses with a sperm it would become diploid.Ĥ) By what evidence might you be able to detect that part of a person's body developed that way? (hint: You wouldn't actually need to see it happen.)ĥ) If the spindle of a meiotic division (of an oocyte) got moved away from the animal pole, then the cleavages would divide to oocyte into more equal parts (i.e. Questions marked with ** will not be on the exam.ġ) Would you expect the first polar body to be haploid, or diploid?Ģ) What about the ploidy of a second polar body?ģ) Suppose that a sperm fused with a second polar body might it then develop into some part of the person who develops from that oocyte? (explain your reasoning, pro or con.)Īnswer: Yes, it might become part of the person's body. I won't ask many such difficult questions. Questions marked with a * are not easy, but you will gain a lot from thinking carefully about them. (There is quite a bit of redundancy in the questions below.) Teleost fish form their neural tube by cavitation, but other vertebrates form their neural tubes by folding. Reorientation of cells to form an epithelial sheet surrounding a water-filled cavity. As this slit elongates, its ends curve downward, and eventually meet each other, forming a circle ("yolk plug stage").Įpithelial fusion Some examples are the fusion of the archenteron with the stomodeum and the fusion of one neural fold with the other neural fold.Ĭavitation (of masses of mesenchymal cells, to form epithelial tubes, or sheets). The blastopore is a curved slit, when formed this way. Involution: A variation of invagination (in frog & salamander gastrulation) in which epithelial cells "roll" into the interior of the embryo. In bird, reptile & mammal embryos, gastrulation is by ingression instead of by invagination. ![]() Partly caused by weakening of cell-cell adhesion, and increased adhesion to extracellular fibers on the side of the epithelium toward which the cells move.įor example, the primary and secondary mesenchyme cells of sea urchin embryos are formed by ingression. Ingression: Movement of epithelial cells out of an epithelium, and change to becoming mesenchymal. In sea urchin gastrulas, it forms near the animal pole. Stomodeum: A small invagination that becomes the mouth. In frog and salamander embryos, the blastopore forms below the equator, on the side of the embryo that will become the posterior. In sea urchin embryos, the blastopore forms at the vegetal pole. Human lungs form by invagination of part of the archenteron.Īrchenteron: The future digestive tract, formed during gastrulation.īlastopore: The opening into the archenteron. Sea urchin gastrulation occurs by invagination. (Caused by contraction of the concave ends of the cells & there are other theories) Invagination: folding inward of part of a epithelial sheet of cells Guess what is meant by "mid-gastrula" and "late-gastrula" stages. Not many cells have moved into the interior, yet. "Early gastrula": An embryo in which gastrulation has just begun. ![]() Gastrulation: Active movement of cells from the surface into the interior of a blastula. (Why not just call them early embryonic cells? It's traditional.)īlastula: A stage of development of a sea urchin or an amphibian in which a hollow cavity has formed inside the embryo (with no connection to the outside)īlastocoel: The hollow (water filled) cavity inside a blastula.īlastocyst: The hollow ball stage of a mammalian embryo. Vegetal pole: The side of an oocyte or early embryo 180 degrees opposite the animal pole.īlastomere: Any cell of a cleavage-stage or blastula-stage embryo It's the location of the polar bodies, and the oocyte nucleus.) Frog eggs rotate with animal pole upward.) I know people who think that yolk density and distribution is what defines the animal pole, but they are wrong. (In most species, yolk is less concentrated here. Polar bodies: Small cells formed on oocytes by the two meiotic divisions.Īnimal pole: The place on an embryo surface where the polar bodies formed. Some special embryological words: Learn to talk like a pro. Review questions for the first hour exam : For every one of the photographs, drawings and diagrams on the lecture web pages, you ought to be able to write what it depicts, label the parts and explain their significance.įor example, can you identify and describe each of the drawings in this diagram?
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