Embryo Project Encyclopedia Images

In the 1930s, George Beadle and Boris Ephrussi discovered factors that affect eye colors in developing fruit flies. They did so while working at the California Institute of Technology in Pasadena, California. (1) They took optic discs (colored fuchsia in the image) from fruit fly larvae in the third instar stage of development. Had the flies not been manipulated, they would have developed into adults with vermilion eyes. (2) Beadle and Ephrussi transplanted the donor optic discs into the bodies of several types of larvae, including those that would develop with normal colored eyes (brick red), and those that would develop eyes with other shades of red, such as claret, carmine, peach, and ruby (grouped together and colored black in the image). (3a) When implanted into normal hosts that would develop brick red eyes, the transplanted optic disc developed into an eye that also was brick red. (3b) When implanted into abnormal hosts that would develop eyes of some other shade of red, the transplanted optic discs developed into eyes that were vermilion. Beadle and Ephrussi concluded that there was a factor, such as an enzyme or some other protein, produced outside of the optic disc that influenced the color of the eye that developed from the disc.

Fruit flies of the species Drosophila melanogaster develop from eggs to adults in eight to ten days at 25 degrees Celsius. They develop through four primary stages: egg, larva, pupa, and adult. When in the wild, female flies lay their fertilized eggs in rotting fruit or other decomposing material that can serve as food for the larvae. In the lab, fruit flies lay their fertilized eggs in a mixture of agar, molasses, cornmeal, and yeast. After roughly a day, each egg hatches into a larva. The larva eats the material it finds itself in, and for four days it grows into stages of increasing size, called first-, second-, and third-instar stages. This figure shows a third-instar larva. Each larva has sections of tissue called imaginal discs, from which various parts of the adult anatomy develop. This figure shows the imaginal discs that will develop into antennae (colored purple), eyes (colored red), brain (colored blue), and wings (colored green). After four days, the larva turns into a pupa by making a casing, similar to caterpillars, and grows within the casing. After a four-day metamorphosis, the adult fly then emerges from its pupal casing. Adult males look somewhat different from adult females, as the males have darker rear abdomen segments than do females. The warmer the temperature around the eggs, the faster the flies develop to adults.

From a developing embryos three primary germ layers, ectoderm (green), mesoderm (pink) and endoderm (yellow), a variety of differentiated cell types and organ systems arise, far more than are shown here. The three primary germ layers are shown during the gastrula stage because they become distinct at the gastrula stage. The germ cells (blue) are pre- cursors to sperm and egg cells, and they are set aside early in development, and are thought to arise from the ectoderm.

This image shows a chicken (Gallus gallus) embryo undergoing gastrulation in stage four (18-19 hrs after laying) according to the Hamburger-Hamilton staging series. At this point in time the chicken embryo is a blastoderm (shown in blue). The first magnification of the embryo shows that the blastoderm cell layers have thickened to form the primitive streak and Hensen's node. The primitive streak extends from the posterior (P) region to the anterior (A) region. The second rectangular magnification shows the blastoderm cross-sectioned through the primitive streak. The cross-section shows the blastoderm's two cell layers, the epiblast and the hypoblast. The fluid filled cavity between the two cell layers is the blastocoel. The space left between the hypoblast cell layer and the yolk is called the subgerminal cavity.

A 3-D fate map of the chicken (Gallus gallus) embryo with the prospective point of ingression and yolk. The area where the primitive streak will form during gastrulation is shown. The anterior- posterior axis is shown by labeling the anterior and posterio ends (A) and (P). Different colors indicate prospective fates of different regions of the epiblast after gastrulation. The turquoise shaded region represents the prospective ectoderm, the lavender shaded region represents the prospective mesoderm, the dark blue shaded region represents the prospective endoderm, and the white shaded region represents the prospective extraembryonic area.

Illustration of the movement of the three hemispheres of cells, the animal cap (dark green) the marginal zone (lime green) and the ventral cap (yellow) during frog gastrulation. The external view column (images a.1-a.6) shows gastrulation as it occurs on the outside of the embryo. The cross-section view column (images b.1-b.6) shows the internal view of gastrulation. The cross-sections are through the middle of the embryo.

In 1935, George Beadle and Boris Ephrussi developed a technique to transplant optic discs between fruit fly larvae. They developed it while at the California Institute of Technology in Pasedena, California. Optic discs are tissues from which the adult eyes develop. Beadle and Ephrussi used their technique to study the development of the eye and eye pigment. (1) The experimenter dissects a donor larva, which is in the third instar stage of development, and removes the optic disc (colored red) with a micropipette. Because the antenna disc is attached to the optic disc, they are often removed and transplanted together. (2) The experimenter then implants the optic disc into a host larva, in the part of the host that will develop into an adult abdomen. As the host larva matures to adulthood, the implanted optic disc develops into an eye inside the body cavity of the adult. (3) The adult host has an eye within its body, which Beadle and Ephrussi found by dissecting the adult hosts. If the antenna disc was also transplanted, sometimes the resulting eye developed with an antenna attached.