Chapter One Terms

early-stage embryo consisting of a sphere of cells surrounding an inner fluid-filled cavity, the blastocoel.

a fluid filled cavity that forms in the animal hemisphere of early amphibian and echinoderm embryos, or between the epiblast and hypoblast of avian, reptilian and mammalian blastoderm-stage embyros.

the invagination point where gastrulation begins, in deutrostomes, this marks the site of the anus, in protostomes, this marks the site of the mouth.

a series of rapid mitotic cell divisions following fertilization in many early embryos; cleavage divides the embryo without increasing its mass.

study of how anatomy changes during the development of different organisms.

the series of cell types starting from an undifferentiated, pluripotent stem cell through stages of increasing differentiation, to the terminally differentiated cell type.

embryo made from tissues of more than one genetic source

the process of progressive and continuous change that generates a complex multicellular organisms from a single cell, development occurs throughout embryogenesis, maturation to the adult form, and continues into senescene.

refers to the two-layer animals of certain phlya, such as the proiferans (sponges) and ctenophores (comb jellies), that lack a true mesoderm, in contrast to triploblastic animals

abnormality or congenital defect caused by exogenous agents (teratogens) such as plants, chemicals, viruses, radiation, or hyperthermia.

the study of animal development from fertilization to hatching or birth

the view supported by Aristotle and William Harvey that the organs of the embryo are formed de novo ("from scratch") at each generation.

meaning outside; the cells that remain on either the outside (amphib) or dorsal (avian, mammal) surface of the embryo following gastrulation. Of the 3 germ layers the ectoderm is the one that forms the nervous system from the neural tube and neural crest and also generates the epidermis covering the embryo.

meaning within; the innermost germ layer; forms the epithelial lining of the respiratory tract, the gastrointestinal tract, and the accessory organs (liver, pancreas) of the digestive tract. In the amphibian embryo, the yolk-containing cells of the vegetal hemisphere become endoderm. In mammalian and avian embryos, the endoderm is the most ventral of the three germ layers, continuous with the yolk sack epithelium.

fusion of male and female gametes followed by fusion of the haploid gamete nuclei to restore the full complement of chromosomes characteristic of the species and initiation in the egg cytoplasm of those reactions that permit development to proceed.

the haploid nucleus of the egg.

diagrams that follow cell lineages from specific regions of the embryo in order to "map" larval or adult structures onto the region of the embryo from which they arose, the superimposition of a map of "what is to be" onto a structure that has yet to develop these organs.

compounds, such as fluorescein and green fluorescent protein (GFP), that emit bright light at a specific wavelength when excited with ultraviolet light.

a specialized reproductive cell through which sexually reproducing parents pass chromosomes to their offspring; sperm or an egg.

the complete DNA sequence of an individual organism.

a process involving movement of the blastomeres of the embryo relative to one another resulting in the formation of the three germ layers of the embryo.

a stage of the embryo following gastrulation that contains the three germ layers that will interact to generate the organs of the body.

a group of cells set aside from the somatic cells that form the rest of the embryo for reproductive function, consists of the cells of the gonads (ovary and testis) that undergo meiotic cell divisions to generate the gametes.

the production of gametes.

one of the three layers of the vertebrate embryo, ectoderm, mesoderm, and endoderm, generated by the process of gastrulation, that will form all of the tissues of the body except for the germ cells.

meaning "complete", refers to a cell division (cleavage) pattern in the embryo in which the entire egg is divided into smaller cells, as it is in frogs and mammals.

structures and/or their respective components whose similarity arises from their being derived from a common ancestral structure, for example, the wing of a bird and the forelimb of a human.

the sexually immature stage of an organism, often significantly different appearance that then adult and frequently the stage that lives the longest and is used for feeding or dispersal.

changing from one form to another, such as the transformation of an insect larva to a sexually mature adult or a tadpole to a frog.

the haploid nucleus of the sperm.

a unique division process occuring only in germ cells, to reduce the number of chromosomes to a haploid complement, all other cells divide by mitosis, meiosis differs from mitosis in that (1) meiotic cells undergo two cell divisions without an intervening period of DNA replication, and (2) homologous chromosomes (each consisting of two sister chromatids joined at a kinetochore) pair together and recombine genetic material.

meros meaning "part"; refers to the cell division (cleavage) pattern in zygotes containing large amounts of yolk, wherein only a portion of the cytoplasm is cleaved. The cleavage furrow does not penetrate the yolky portion of the cytoplasm because the yolk platelets impede membrane formation there, only part of the egg is destined to become the embryo, while the other portion--the yolk--serves as nutrition for the embryo, as in incests, fish, retiles, and birds.

mesos meaning "between"; the middle of the three embryonic germ layers, lying between the ectoderm and the endoderm, the mesoderm gives rise to muscles and skeleton; connective tissue; the reproductive organs; and to kidneys, blood, and most of the cardiovascular tissue.

cells containing the pigment melanin, derived from neural crest cells and undergo extensive migration to all regions of the epidermis.

abnormalities caused by genetic events such as gene mutations, chromosomal aneuploidies, and translocations.

a transient mesodermal rod in the most dorsal portion of the embryo that plays an important role in inducing and patterning the nervous system.

refers to an embryo during neurulation (i.e., while the neural tube is forming).

the embryonic precursor to the central nervous system (brain and spinal cord).

a transient band of cells, arising from the lateral edges of the neural plate, that joins the neural tube to the epidermis, it gives rise to a cell population--the neural crest cells--that detach during formation of the neural tube and migrate to form a variety of cell types and structures, including sensory neurons, enteric neurons, glia, pigment cells, and (in the head) bond and cartilage.

interactions between, and rearrangement of, cells of the three germ layers to produce tissues and organs.

the view, supported by the early microscopist, Marcello Malpighi, that the organs of the embryo are already present, in miniature form, within the egg (or sperm), a corollary emboitment, stated that the next generation already existed in a prefigured state within the germ cells of the first prefigured generation, thus ensuring that the species would remain constant.

also called a branchial arches, these are bars of mesenchymal tissue derived from paraxial mesoderm, lateral plate mesoderm, and neural crest cells; found in the pharyngeal region (near the pharynx) of the vertebrate embryo, the arches will form gill supports in fishes and many skeletal and connective tissue structures in the face, jaw, mouth, and larynx in other vertebrates.

soma meaning "body"; cells that form the body, all cells in the organism that are not germ cells.

segmental block or ball of mesoderm formed from paraxial mesoderm adjacent to notocord (the axial mesoderm); differentiates to form, initially, sclerotome and dermamyotome; the latter goes on to form dermotome and myotome; somites will form the axial skeleton, all skeletal muscle, and the dorsal dermis, tendons, joints, and dorsal aortic cells.

meaning "happening together"; several malformations or pathologies that occur concurrently, genetically based syndromes are caused either by (1) a chromosomal event--such as a trisomy--where several genes are deleted or added, or (2) by one gene having many effects.

"three layer" animals containing tissues derived from the three germ layers, ectoderm, mesoderm, and endoderm, as opposed to diploblastic animals that lack mesoderm tissue.

meaning "monster formers"; exogenous agents that cause disruptions in development resulting in teratogenesis, the formation of congenital defects; teratology is the study of birth defects and of how environmental agents disrupt normal development.

the study of birth defects and of how environmental agents disrupt normal development.

the bottom portion of the amphibian egg, containing yolk, which serves as food for the developing embryo; the yolk-filled cells divide more slowly and undergo less movement during embryogenesis (and hence are like plants or "vegetal")

stains used to label living cells without killing them; when applied to embryos, vital dyes have been used to follow cell migration during development and generate fate maps of specific regions of the embryo.

a fertilized egg with a diploid chromosomal complement in its zygote nucleus generated by fusion of the haploid male and female pronuclei.

the discipline that studies embryonic and other developmental processes.

the stages of development between fertilization and hatching.

a diploid formed from the merge of the female pronucleus and male pronucleus.

the study of how changes in development may cause evolutionary change and of how an organism's ancestry may constrain the types of changes that are possible.

animals that are born from eggs such as birds, frogs, and most invertebrates.

animals that give live birth such as placental mammals.

animals that produce an egg that hatches inside the body such as certain reptiles and sharks.

the small region of the egg containing the yolk-free cytoplasm that gives rise to the embryo.

cells that are tightly connected to one another in sheets or tubes.

cells that are unconnected to one another and operate as indepentent units.