AP Bio Chapter 47 – Animal Development
Review Guide
Fertilization and Beyond, the Three Stages that Develop
the Animal Body
Organogenesis
Overview:
The organs of the animal body develop from specific portions of the three embryonic
germ layers. Early events in organogenesis in vertebrates include formation of the
notochord by condensation of dorsal mesoderm, development of the neural tube from
infolding of the ectodermal neural plate, and formation of the coelom from splitting of
lateral mesoderm.
Vocab:
Notochord - A longitudinal, flexible rod that runs along the dorsal axis of an animal's
body in the future position of the vertebral column
Neural Tube - A tube of cells running along the dorsal axis of the body, just dorsal to
the notochord. It will rise to the central nervous system
Neural Crest - A band of cells running along the border where the neural tube pinches
off from the ectoderm. The cells migrate to various parts of the embryo and form the
pigment cells in the skin, bones of the skull, the teeth, the adrenal glands, and parts of
the peripheral nervous system
Somites -Paired blocks of mesoderm just lateral to the notochord of a vertebrate
embryo
Developmental Adaptations of Amniotes
Overview:
The embryos of birds, other reptiles, and mammals develop within a fluid–filled sac
that is contained within a shell or the uterus. In these organisms, the three germ layers
give rise not only to embryonic tissue but also to the four extraembryonic membranes:
the amnion, chorion, yolk sac, and allantois.
Vocab:
Amniote - Member of a clade of tetrpods that have an amniotic egg containing
specialized membranes that protect the embryo, including mammals and birds and
other reptiles
Extraembryonic Membranes - Four membranes (yolk sac [1st site of blood cells and
circulatory system function], amnion [innermost extraembryonic membrane, encloses a
fluid-filled sac in which the embryo is suspended], chorion [contributes to the formation
of the mammalian placenta], allantois [serves as a repository for the embryo's
nitrogenous waste] ) that support the developing embryo in mammals and birds and
other reptiles
Mammalian Development
Overview:
The eggs of placental mammals are small and store few nutrients. They exhibit
holoblastic cleavage and show no obvious polarity. Gastrulation and organogenesis,
however, resemble the processes in birds and other reptiles. After fertilization and early
cleavage in the oviduct, the blastocyst implants in the uterus. The trophoblast initiates
formation of the fetal portion of the placenta, and the embryo proper develops from a
single layer of cells, the epiblast, within the blastocyst. Extraembryonic membranes
homologous to those of birds and other reptiles function in intrauterine development.
Vocab:
Blastocyst - An embryonic stage in mammals; a hollow ball of cells produced one week
after fertilization in humans
Inner Cell Mass - A cluster of cells in a mammalian blastocyst that protrudes into one
end of the cavity and subsequently develops into the embryo proper and some of the
extraembryonic membranes
Trophblast - The outer epithelium of the blastocyst, which forms the fetal part of the
placenta
The Developmental Fate of Cells
Fate Mapping
Overview:
Experimentally derived fate maps of embryos have shown that specific regions of the
zygote or blastula develop into specific parts of older embryos.
Vocab:
Fate Maps - Territorial diagram of embryonic development that reveals the future
development of individual cells and tissues.
Developmental Potential - The range of structures that it can give rise to
Establishing Cellular Asymmetries
Overview:
In non–amniotic species, unevenly distributed cytoplasmic determinants in the egg cell
are important in establishing the body axes and in setting up differences between the
blastomeres resulting from cleavage of the zygote. Cells that receive different
cytoplasmic determinants undergo different fates. In amniotes, local environmental
differences play the major role in establishing initial differences between cells and later
the body axes. As embryonic development proceeds, the potency of cells becomes
progressively more limited in all species.
Vocab:
Totipotent - Describing a cell that can give rise to all parts of an organism
Cell Fate Determination and Pattern Formation by Inductive Signals
Overview:
Cells in a developing embryo receive and interpret positional information that varies
with location. This information is often in the form of signal molecules secreted by cells
in special “organizer” regions of the embryo, such as the dorsal lip of the blastopore in
the amphibian gastrula and the AER and ZPA of the vertebrate limb bud. The signal
molecules influence gene expression in the cells that receive them, leading to
differentiation and the development of particular structures.
Vocab:
Induction - The switching on of a set of genes that make the receiving cells differentiate
into a specific tissues
Pattern Formation - The ordering of cells into specific three-dimensional structures, an
essential part of shaping an organism and its individual parts during development
Positional Information - Signals to which genes regulating development respond,
indicating a cell's location relative to other cells in an embryonic structure.
Apical Ectodermal Ridge (AER) - A limb-bud organizer region consisting of a thickened
area of ectoderm at the tip of a limb bud
Zone of Polarizing Activity (ZPA) - A limb-bud organizer region consisting of a block of
mesoderm located where the posterior of the bud is attached to the body