Key Concepts & Study Questions for BIOL 303 (F2013) Lecture Set 1
• gastrulation and germ layers
• fate maps
1. What do we mean when we refer to the “development” of an organism?
The “development” of an organism is the process of progressive and
continuous change that generates a complex multicellular organism from a
single cell Development occurs throughout embryogenesis, maturation to the
adult form, and continues into senescence.
2. Define the following terms: gamete, zygote, cleavage, blastomere, morula, blastula,
blastocoel, gastrulation, gastrula, germ layer, triploblastic, diplobasltic, ectoderm,
mesoderm, endoderm, organogenesis, germ cells, somatic cells.
Gamete: A specialized reproductive cell through which sexually reproducing
parents pass chromosomes to their offspring; a sperm or an egg.
Zygote: A fertilized egg with a diploid chromosomal complement in its zygote
nucleus generated by fusion of the haploid male and female pronuclei.
Cleavage: A series of rapid mitotic cell divisions following fertilization in
many early embryos; cleavage divide the embryo without increasing its mass.
Blastomere: A cleavagestage cell resulting from mitosis.
Morula: Vertebrate embryo of 1664 cells;, precedes the blastula or
Blastula: Earlystage embryo consisting of a sphere of cells surrounding an
inner fluidfilled cavity, the blastocoel.
Blastocoel: Fluidfilled cavity of a blastula.
Gastrulation: 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.
Gastrula: A stage of the embryo following gastrulation that contains the
three germ layers that will interact to generate the organs of the body.
Germ Layer: One of the three layers of the vertebrate embryo generated by
the process of gastrulation, that will form all of the tissues of the body except
for germ cells.
Triploblastic: Having a body derived from three germ/embryonic cell layers
(ectoderm, mesoderm, endoderm, most animals).
Diploblastic: Having a body derived from two germ/embryonic cell layers
(ectoderm, endoderm, sponges).
Ectoderm: The cells that remain on either the outside (amphibian) or dorsal
(avian, mammalian) surface of the embryo following gastrulation. Of the
three germ layers, the ectoderm is the one that forms the nervous system
from the neural tube and the neural crest and also generates the epidermis
covering the embryo
Mesoderm: 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.
Endoderm: The innermost germ layer; forms the epithelial lining of the
respiratory tract, the gastrointestinal tract and the accessory organs (e.g.,
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.
Organogenesis: Interactions between, and rearrangement of, cells of the
three germ layers to produce tissues and organs. (Many organs and tissues
are composed of cells derived from different germ layers. Some cells undergo
extensive migration from place or origin to final location).
Germ Cells: 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 testis) that undergo meiotic cell divisions to generate the
gametes. Somatic Cells: Cells that form the body; all cells in the organism that are not
3. What is h