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Temperature-Dependent Sex Determination in Reptiles
The sex of a reptile embryo partly results from the production of sex hormones during development, and one process to produce those hormones depends on the temperature of the embryo's environment. The production of sex hormones can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination, also called genetic or chromosomal sex determination, an organism's genes determine which hormones are produced.
Format: Articles
Subject: Experiments
Mitochondria
All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism. The theory for how mitochondria evolved, proposed by Lynn Margulis in the twentieth century, is that they were once free-living organisms.
Format: Articles
Beadle and Ephrussi Show that Something Besides Eye Tissue Determines Eye Color in Fruit Flies
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.
Format: Graphics
Subject: Experiments, Organisms
A Fate Map of the Chick Embryo
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.
Format: Graphics
The Blastoderm in Chicks During Early Gastrulation
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.
Format: Graphics
Neurospora crassa Life Cycle
This diagram shows the life cycle of Neurospora crassa, a mold that grows on bread. N. crassa can reproduce through an asexual cycle or a sexual cycle. The asexual cycle (colored as a purple circle), begins in this figure with (1a) vegetative mycelium, which are strands of mature fungus. Some of the strands form bulbs (2a) in a process called conidiation. From those bulbs develop the conidia, which are spores. Next, (3a) a single conidium separates from its strand and elongates until it forms mycelium.
Format: Graphics
Beadle and Ephrussi’s Technique to Transplant Optic Discs between Fruit Fly Larvae
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.
Format: Graphics
Subject: Technologies, Experiments, Organisms
Fruit Fly Life Cycle
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.
Format: Graphics
The Process of Gastrulation in Frog Embryos
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.
Format: Graphics
Frog Embryo in the Blastula Stage
Illustration of the animal-vegetal gradient in Xenopus laevis ( African clawed frog) eggs after fertilization. During fertilization, the sperm s point of entry determines the future dorsal side (shaded) and ventral side (unshaded) of the embryo. The prospective ventral side of the embryo forms on the side where the sperm enters while the prospective dorsal side forms opposite the sperm s point of entry.
Format: Graphics
1895 Course Photographs, Students & Faculty (Overlay)
Format: Photographs
Subject: People, Organizations