In the case of the French flag model. we assume a source of morphogen at one end and a sink at the other and that the concentrations of morphogen at both ends are kept constant but are different from each other. If the cells can respond to threshold concentrations of the morphogen, Thresholds can represent the

a. amount of morphogen that must bind to receptors to activate an intracellular signaling system. 

b. concentrations of transcription factors required to activate particular genes.

c. concentration at any point effectively provides positional information.

d. amount of morphogen that must bind to receptors to inactivate an extracellular signaling system.

#Question id: 4984

#Unit 11. Evolution and Behavior

A hypothetical mutation in a squirrel population produces organisms with eight legs rather than four. Further, these mutant squirrels survive, successfully invade new habitats, and eventually give rise to a new species. The initial event, giving rise to extra legs, would be a good example of

#Question id: 4985

#Unit 11. Evolution and Behavior

The loss of ventral spines by modern freshwater sticklebacks is due to natural selection operating on the phenotypic affects of Pitx1 gene

#Question id: 4986

#Unit 11. Evolution and Behavior

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (i.e., halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap. If these fly species lost the ability to fly independently of each other as a result of separate mutation events in each lineage, then the flightless condition in these species could be an example of

#Question id: 4987

#Unit 11. Evolution and Behavior

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (i.e., halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.In each fly species, the entire body segment that gave rise to the original flight wings is missing. The mutation(s) that led to the flightless condition could have

#Question id: 4988

#Unit 11. Evolution and Behavior

If the foods preferred by each species are found on different parts of the island, and if the flies mate and lay eggs on their food sources, regardless of the location of the food sources, then the speciation events involving these fly species may have been driven, at least in part, by which of the following?

#Question id: 4989

#Unit 11. Evolution and Behavior

If the malesʹ halteres have species-specific size, shape, color, and use in courtship displays, and if the speciesʹ ranges overlap, then the speciation events may have been driven, at least in part, by which of the following?