Biology Developmental Biology & Embryology Flashcards

What term describes the series of rapid mitotic cell divisions that occur immediately after fertilization, producing smaller and smaller cells?

Answer: Cleavage

Cleavage refers to the rapid mitotic divisions following fertilization that divide the zygote into blastomeres without significant cell growth between divisions.

What is the inner cell mass (embryoblast) of the blastocyst primarily responsible for forming?

Answer: The embryo proper and some extraembryonic structures

The inner cell mass of the blastocyst gives rise to the embryo proper as well as some extraembryonic membranes, and is the source of embryonic stem cells.

During gastrulation, which three primary germ layers are established?

Answer: Ectoderm, mesoderm, and endoderm

Gastrulation establishes the three primary germ layers—ectoderm, mesoderm, and endoderm—from which all tissues and organs of the body will ultimately develop.

Which germ layer gives rise to the central nervous system, including the brain and spinal cord?

Answer: Ectoderm

The ectoderm, specifically the neuroectoderm, gives rise to the central nervous system through the process of neurulation.

What is neurulation?

Answer: The process by which the neural plate folds and fuses to form the neural tube

Neurulation is the embryonic process by which the flat neural plate (derived from ectoderm) folds at the neural folds and fuses to create the hollow neural tube, precursor to the brain and spinal cord.

What is the primitive streak in early vertebrate development?

Answer: A thickening of the epiblast that marks the site of gastrulation and establishes the body axis

The primitive streak is a thickening and groove along the midline of the epiblast that marks the initiation of gastrulation and defines the anterior-posterior axis of the vertebrate embryo.

Which extraembryonic membrane functions primarily in gas exchange and metabolic waste storage in bird and reptile embryos, and contributes to the umbilical cord in mammals?

Answer: Allantois

The allantois is a sac-like outgrowth of the hindgut that stores nitrogenous waste and facilitates gas exchange in reptiles and birds; in mammals it contributes blood vessels to the umbilical cord.

What is embryonic induction?

Answer: The ability of one group of cells to signal adjacent cells to adopt a specific developmental fate

Embryonic induction occurs when an inducing tissue releases signals that cause a responding tissue to change its developmental trajectory, as in the notochord inducing neural tube formation.

Hox genes are critical to animal development primarily because they:

Answer: Determine positional identity along the anterior-posterior body axis by encoding transcription factors

Hox genes encode homeodomain transcription factors that specify segment identity along the anterior-posterior axis; mutations cause homeotic transformations where one body segment adopts the identity of another.

What is the role of apoptosis in normal embryonic development?

Answer: It sculpts structures by removing specific cells, such as the interdigital webbing between developing fingers

Apoptosis (programmed cell death) is essential for normal morphogenesis; it removes cells between developing digits, shapes the nervous system by eliminating excess neurons, and remodels many organ systems.

What are neural crest cells and why are they significant?

Answer: A highly migratory population derived from the dorsal neural tube that gives rise to diverse cell types including peripheral neurons, melanocytes, and craniofacial cartilage

Neural crest cells are a multipotent, migratory population that delaminate from the dorsal neural tube and travel throughout the embryo, contributing to an extraordinary variety of tissues sometimes called the 'fourth germ layer.'

Which term describes the process by which embryonic cells become increasingly structurally and functionally specialized during development?

Answer: Differentiation

Differentiation is the process by which cells acquire distinct molecular, structural, and functional characteristics as they develop from a pluripotent state toward a specialized cell type.

What is a morphogen gradient?

Answer: A concentration gradient of a signaling molecule that provides cells with positional information to guide their developmental fate

Morphogens are signaling molecules that form concentration gradients across a tissue; cells interpret their position in the gradient to adopt different fates, explaining how a field of cells generates diverse cell types.

What is organogenesis?

Answer: The process by which the three primary germ layers differentiate into the specific organs and organ systems of the body

Organogenesis is the embryonic stage following gastrulation during which the three germ layers interact and differentiate to form all recognizable organs and organ systems.

What is the primary function of the amnion in amniotic vertebrates?

Answer: It encloses the embryo in a fluid-filled cavity that cushions it from mechanical shock and prevents desiccation

The amnion forms a fluid-filled (amniotic fluid) compartment around the embryo, providing physical protection from shock and maintaining a moist environment—an adaptation critical for terrestrial reproduction.

The trophoblast cells of the blastocyst are primarily responsible for:

Answer: Implanting into the uterine wall and forming the fetal contribution to the placenta

Trophoblast cells form the outer layer of the blastocyst, invade the uterine endometrium during implantation, and give rise to the chorion and fetal side of the placenta.

What is cellular determination in developmental biology?

Answer: The irreversible commitment of a cell to a particular developmental fate, maintained even if the cell is transplanted to a new location

Determination refers to the irreversible commitment of a cell to a specific developmental pathway; once determined, a cell differentiates along that pathway regardless of its new environment, distinguishing it from earlier, reversible specification.

Which description best defines stem cells in a developmental biology context?

Answer: Undifferentiated cells with the capacity for self-renewal and the ability to differentiate into one or more specialized cell types

Stem cells are defined by two key properties: self-renewal (the ability to divide and produce more stem cells) and potency (the ability to differentiate into specialized cell types), making them fundamental to development and tissue maintenance.

What is hemimetabolism (incomplete metamorphosis) in insects?

Answer: A life cycle consisting of egg, nymph, and adult stages in which the nymph gradually resembles a wingless adult

Hemimetabolism (incomplete metamorphosis) proceeds through three stages—egg, nymph, and adult—where the nymph resembles a miniature wingless adult and undergoes gradual change, unlike holometabolism which includes a pupal stage.

What is the primary developmental significance of the notochord in vertebrate embryos?

Answer: It provides axial structural support and secretes signals that induce the overlying ectoderm to form the neural plate and tube

The notochord is a transient mesodermal rod that defines the body axis, provides structural support, and critically releases Sonic Hedgehog (Shh) and other signals that induce neural tube formation and pattern the surrounding tissues.