Here is your answer I hope it was useful: a striation is any of a number of tiny parallel grooves such as: the scratches left by a glacier on rocks or the streaks or ridges in muscle tissue. Your answer is yes, there are striation across the width of a muscle.
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The lac repressor protein is bound to the operator region of the lac operon when there is no lactose in the medium. When introduced in lactose, it binds to an allosteric site on the repressor causing its to change conformation and release from the operator. This allows the polymerase that is bound to the promoter region to proceed transcription of the lac operon genes (LacZ, Lac A, and Lac Y). Translation of these genes forms enzymes that enable the organism to break down lactose for energy.
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The variation in beak type enables the different individuals in a population to feed on different food sources.
The shape of the beak is key to determining the primary food source of the bird. Certain birds species have specialized beaks, but within populations of those species, there is a variation in beak shape.
This gives the population the ability to respond to changes in the environment and availability of different food sources.
For example, if because of a dry period there is a shortage of fruit, some individuals in the population have the beaks that enable them to feed on other things, survive and leave offspring.