White eyes in drosophila melanogaster result from an x‑linked recessive mutation. occasionally, white‑eyed mutants give rise to offspring that possess white eyes with small red spots. the number, distribution, and size of the red spots are variable. explain how a transposable element, or transposon, could be responsible for this spotting phenomenon. excision of a transposable element out of the eye color locus during eye development produces a patch of cells that produce red pigment. a transposable element is introduced into the regulatory region of the eye color gene and causes gene expression to be reduced, which results in white eyes with red spots. insertion of a transposon upstream of the eye color locus during eye development activates the red pigment production gene in a patch of eye cells. a transposon located within the eye color gene uses reverse transcriptase to produce the normal gene product, which causes white eyes with red spots. transposable elements insert into the eye color locus in the majority of the eye cells, leaving only a patch of eye cells with an active eye color locus that produces red pigment.

Organism, organ system, organs, tissue, cells

Environmental science studies the interactions between the physical, chemical, and biological components of the environment, including their effects on all types of organisms. earth science (also known as geoscience), is an inclusive term for all sciences related to earth (geology, meteorology, oceanogr maphy, etc).  although environmental and earth science cover essentially the same material, environmental science places greater emphasis on the biological realm, while earth science places greater emphasis on the physical realm.    environmental and earth science study the interactions of four major systems or “spheres” (figure 8.6).  the  geosphere  consists of the core, mantle and crust of the earth.the  atmosphere  contains all of the earth’s air and is divided into troposphere, stratosphere, mesosphere, thermosphere and ionosphere.the  hydrosphere  contains all of the solid, liquid and gaseous water on earth, extending from the depths of the sea to the upper reaches of the troposphere where water is found.  ninety-seven percent of the hydrosphere is found in salty oceans, and the remainder is found as vapor or droplets in the atmosphere and as liquid in ground water, lakes, rivers, glaciers and snowfields.  the  biosphere  is the collection of all earth’s life forms, distributed in major life zones known as biomes:   tundra, boreal forest, temperate deciduous forest, temperate grassland, desert, savannah, tropical rainforest, chaparral, freshwater, and marine.although the four systems have their unique identities, there is substantial interaction between them.  environmental scientists study the effects of events in one sphere on the other spheres. for example, a volcanic eruption in the geosphere may cause profound direct and indirect effects on the hydrosphere, atmosphere and biosphere as follows: example 1 (volcano)    on may 18, 1980, mount saint helens, in the state of washington, erupted.  this event altered the surrounding environment, and provided scientists with an opportunity to study the effects of volcanic eruptions on the geosphere, hydrosphere, atmosphere and biosphere.  such studies are vital because volcanic eruptions will continue to occur, and will have increasing impact on humans as people continue to settle lands closer to dormant volcanoes. the following are but a few of the myriad of interactions resulting from a volcanic