Developmental Biology Terms Starting With F
Developmental Biology Glossary: F
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Fate Map
/ FAYT map / · Old English ft, result; Latin mappa, cloth
Fate Map is a diagram showing which regions of an early embryo are expected to give rise to particular tissues or organs in the mature animal.
Fate maps are constructed by labeling specific regions of an early embryo with fluorescent dyes, radioactive markers, or genetic reporters, then tracking where those labeled cells and their descendants end up in the older embryo or adult. Amphibian fate maps revealed that cells from distinct blastula regions contribute to neural tissue, notochord, mesoderm, endoderm, and other structures in largely non-overlapping territories. These maps show typical outcomes rather than fixed destinies, since embryonic regions retain some developmental plasticity, with the degree varying among species and cell types.
Modern approaches combine single-cell transcriptomics with live imaging to track cell lineages at a resolution Walter Vogt could not have imagined when he pioneered the technique in the 1920s.
Walter Vogt created the first comprehensive fate maps of amphibian embryos in the 1920s by pressing small pieces of colored agar paste against specific regions of frog blastulae, a method so gentle it left development undisturbed while marking thousands of cells at once.
A fate map assigns a fixed destiny to every cell in the embryo. Fate maps record statistically typical outcomes, and many embryonic cells retain the capacity to change fate if transplanted to a new position.
In zebrafish (Danio rerio), researchers labeled individual blastomeres at the 32-cell stage with fluorescent dye and found that a single dorsal blastomere contributes descendants to roughly 30 percent of the neural tube. Ventral blastomeres at the same stage contributed almost no cells to neural tissue, demonstrating the predictive power of positional fate mapping.
Fertilization Envelope
/ fer-TIL-ih-ZAY-shun EN-veh-lope / · Latin fertilitas; envoloper, to wrap
Fertilization Envelope is a protective barrier that rises around the egg of sea urchins and other marine animals within seconds of sperm entry, blocking additional sperm from reaching the egg membrane.
The fertilization envelope forms when cortical granules beneath the egg surface undergo exocytosis, releasing enzymes and structural proteins that lift the vitelline layer away from the plasma membrane. This elevated envelope creates a physical and biochemical barrier that prevents additional sperm from penetrating and fusing with the egg, a process called blocking polyspermy. Enzymes released into the perivitelline space harden the envelope by cross-linking its proteins, a reaction that completes within about 60 seconds of sperm entry in sea urchins (Strongylocentrotus purpuratus).
Mammals rely less on envelope elevation and more on zona pellucida modification, in which cortical granule enzymes alter sperm-binding glycoproteins to prevent secondary sperm attachment.
A single sea urchin egg contains roughly 15,000 cortical granules arranged just beneath the plasma membrane, and all of them fuse with the membrane and release their contents within about one minute of fertilization.
Reproductive System Fun Facts →The fertilization envelope forms slowly over several minutes after sperm entry. The envelope begins rising within 10 to 15 seconds of sperm entry in sea urchins, driven by a wave of cortical granule exocytosis that sweeps across the egg surface from the point of sperm contact.
In the purple sea urchin (Strongylocentrotus purpuratus), the fertilization envelope lifts approximately 10 micrometers from the egg surface within 15 seconds of sperm contact. Experiments blocking cortical granule exocytosis with calcium chelators leave the vitelline layer flat and allow multiple sperm to fuse with the same egg, confirming that envelope elevation is the primary polyspermy block in this species.
Fetal Development
/ FEE-tul deh-VEL-up-ment / · Latin fetus, offspring
Fetal Development is the period of prenatal growth that begins after the major body structures have been established, during which the fetus increases dramatically in size and its organ systems mature toward functional independence.
Fetal development begins around week 9 in humans, when major organ systems are already present, and continues until birth as fetal mass increases from less than 5 grams to over 3 kilograms. Facial structures become recognizable, limbs acquire distinct fingers and toes, and external genitalia differentiate during the first half of this period. Lung maturation depends on the progressive production of pulmonary surfactant, which begins around week 24 but reaches adequate levels only near week 36, explaining why infants born before 28 weeks require respiratory support.
The nervous system expands rapidly throughout the fetal period, with the cerebral cortex generating most of its neurons between weeks 12 and 20 at a rate estimated at 250,000 new neurons per minute.
Fetal taste buds are functional by week 14, and studies of amniotic fluid composition show that fetuses swallow more fluid when it contains sweet compounds introduced experimentally, suggesting flavor preferences begin forming months before birth.
All body parts first appear during the fetal stage. The basic plans for major organs, including the heart, brain, and limb buds, form during the embryonic period, which ends at week 8 in humans, before the fetal period begins.
In human fetuses, the kidneys begin producing urine by week 10 and contribute the majority of amniotic fluid volume by the second trimester. By week 20, fetal urine output reaches approximately 7 to 14 milliliters per hour, making the fetal kidney a major regulator of amniotic fluid balance well before birth.
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