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Unit 7: Genetics of Development
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Animations

CyclopamineCyclopamine
The normal Hedgehog signaling pathway is blocked by the receptor antagonist cyclopamine.
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Hedgehog GradientHedgehog Gradient
The level of Hedgehog protein a cell binds during development can influence its fate.
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Hedgehog SignalingHedgehog Signaling
The Hedgehog signaling pathway triggers expression of other developmentally important genes.
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HomeoboxHomeobox
The color-shaded regions represent homeotic genes called Hox genes. The dark band within each gene represents a 180-base-pair region called the homeodomain.
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HomeodomainHomeodomain
A 3-D model of a protein with a homeodomain, a "helix-turn-helix" motif that acts as a transcription factor by binding directly to DNA to turn on other genes.
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Retinoic Acid Retinoic Acid
A retinoic acid gradient controls the activation of many developmentally important genes. Disruptions in the embryo's retinoic acid levels can lead to malformation of the embryo.
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Spatial and Temporal ColinearitySpatial and Temporal Colinearity
Hox genes display spatial colinearity — genes at one end of the chromosome are expressed at the head end of an embryo while genes at the other end are expressed toward the tail end. Vertebrate Hox genes also show temporal colinearity — genes at the head end are expressed before those at the tail end.
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Images

Chick embryo Blastula
A photograph of an early stage blastula from the Xenopus laevis frog.
Chick embryo Chick embryo
A microphotograph of a chick embryo.
Colinearity Colinearity
Genes that are expressed at the anterior end of an animal are located at the more anterior region of the chromosome. Likewise, posteriorly expressed genes reside on the posterior end of the chromosome. This is referred to as spatial colinearity.
Coordinate, gap, pair-rule, and segment polarity genes Coordinate, gap, pair-rule, and segment polarity genes
The cascade of developmental genes in segmentation in Drosophila. Maternal effect/ coordinate genes set the anterior-posterior axes. The embryo is subdivided into progressively smaller regions by the actions of each class of segmentation genes.
Corn lilly Corn lilly
A substance found in the corn lilly plant, Californicum veratrum, called cyclopamine, is the cause of birth defects in lambs.
Cyclopic lamb Cyclopic lamb
This lamb's mother ate a poisonous plant, the corn lilly, which contains a compound called cyclopamine. This compound inhibits the action of the Sonic Hedgehog protein, which is involved in the formation of the neural system.
Deformed zebrafish embryo Deformed zebrafish embryo
This embryo was treated with retinoic acid, which causes neurological damage.
Drosophila embryo with bicoid protein stain Drosophila embryo with bicoid protein stain
This is a 2-hour-old drosophila embryo that shows the expression of the bicoid protein. The bicoid protein forms a gradient with the highest expression at the anterior end (left side in this photo) of the embryo.
Drosophila eye Drosophila eye
Electron microscope image of a fly eye (Drosophila melanogaster)
Drosophila with antennapedia mutation Drosophila with antennapedia mutation
When Drosophila has a mutation in the antennapedia gene, legs will grow out of its head.
Fate map Fate map
Left: A photograph of an early stage blastula from the Xenopus laevis frog. Right: A representation of a fate map.
Fruit fly With extra eyes Fruit fly with extra eyes
The head of a fruit fly, Drosophila melanogaster, viewed by scanning electron microscope (380x magnification). Targeted expression of the eyeless gene induced the formation of the eye facets on the antenna (to the lower-right of the eye), which are very similar to the facets of the normal eye. This dentifies eyeless as the master control gene of eye morphogenesis.
HEP-2 cells in culture HEP-2 cells in culture
Hep-2 cells in culture (200x magnification, crystal violet stain, high density)
Maternal inheritance Maternal inheritance
Reciprocal F1 crosses involving maternal effect genes can produce different phenotypes.
Monkey kidney cells in culture Monkey kidney cells in culture
Monkey kidney cells in culture, showing a typical patch of monolayer cells (100x magnification)
Pancreatic islets Pancreatic islets
The endocrine portion of the pancreas takes the form of many small clusters of cells, called islets of Langerhans, or, simply, islets. Humans have roughly one million islets. In standard histological sections of the pancreas, islets are seen as relatively pale-staining groups of cells embedded in a sea of darker-staining exocrine tissue. This image shows three islets in the pancreas of a horse.
Transcription factor Transcription factor
The triangle represents a transcription factor binding to DNA in the nucleus to affect transcription and translation of new proteins.
Undifferentiated embryonic stem cells Undifferentiated embryonic stem cells
Microscopic (5x magnification) view of a colony of undifferentiated human embryonic stems cells. The embryonic stem cell colonies are the rounded, dense masses of cells. The flat, elongated cells in between the embryonic stem cell colonies are fibroblasts that are used as a "feeder layer" on which the embryonic stem cells are grown.
Undifferentiated embryonic stem cells Undifferentiated embryonic stem cells
Microscopic view of a colony of undifferentiated human embryonic stems cells. The embryonic stem cell colonies are the rounded, dense masses of cells. The flat, elongated cells in between the embryonic stem cell colonies are fibroblasts that are used as a "feeder layer" on which the embryonic stem cells are grown.
Whorls Whorls
The tissues that will become floral organs are arranged in concentric whorls of a developing flower.
Zebrafish embryo Zebrafish embryo
This 18-hour-old zebrafish embryo is labeled with a probe that shows the expression of sonic hedgehog mRNA.
Zebrafish embryo with Sonic Hedgehog protein stain Zebrafish embryo with Sonic Hedgehog protein stain
Zebrafish embryo with a stain that shows the gradient of the hedgehog protein.
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