Over Evolutionary History, Many Groups of Organisms That Inhabit Caves

question 19

Essay

Over evolutionary history, many groups of organisms that inhabit caves have lost the organs of sight.For instance, although surface-dwelling crayfishes have functional eyes, several crayfish species that are restricted to underground habitats lack eyes.Opsins are a group of light-sensitive proteins known to have an important function in vision (see Chapter 45), and opsin genes are expressed in eye tissues.Opsin genes are present in the genomes of eyeless, cave-dwelling crayfishes.Two alternative hypotheses that might explain the presence of opsin genes in an eyeless organism are: (1) the genes are no longer experiencing purifying selection because there is no longer selection for function in vision; and (2) the genes are experiencing selection for a function other than vision.How would you investigate these two hypotheses, using the sequences of the opsin genes in various species of crayfishes?

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Definitions:

Dividend Yield

A ratio, computed by dividing the annual dividends paid per share of common stock by the market price per share at a specific date, that indicates the rate of return to stockholders in terms of cash dividend distributions.

Par Value

A dollar amount assigned to each share of stock.

Unusual Items

Non-recurring or rare expenses or revenues that are not expected to happen regularly and are outside the ordinary activities of a business.

Income from Continuing Operations

The profit or loss generated from a company's regular business activities, excluding extraordinary items or discontinued operations.