The treeʹs horizontal axis is a timeline that extends from 100,000 years ago to the present; the vertical axis represents nothing in particular. The labeled branch points on the tree (V—Z) represent various common ancestors. Letʹs say that only since 50,000 years ago has there been enough variation between the lineages depicted here to separate them into distinct species, and only the tips of the lineages on this tree represent distinct species.

According to this tree, what percent of the species seem to be extant (i.e., not extinct)?

#Question id: 13159

#Unit 4. Cell Communication and Cell Signaling

#Question id: 12086

#Unit 10. Ecological Principles

The herbaceous plant Achillea lanulosa is widespread in the Northern Hemisphere. Phenotypic variation in the species has been extensively studied along an altitudinal gradient from sea level to over 3,000 meters. In California there is conspicuous variation in  height; alpine plants are only several centimeters tall  while  those in  the San Joaquin Valley may reach a height of 1.8 meters. Adaptation to different local environments also results in variation in physiological processes such as photosynthetic rate, resistance to cold, and the timing of dormancy.

The genetic polymorphism found in Achillea lanulosa is most likely maintained primarily by

#Question id: 8689

#Unit 9. Diversity of Life Forms

Which of the following statements best describes the rationale for applying the principle of maximum parsimony in constructing phylogenetic trees?

#Question id: 28239

#Unit 5. Developmental Biology

 In principles of stem cell regulation involve Extracellular mechanisms leading to intracellular changes, for these changes various intracellular regulatory mechanisms include, except? 

#Question id: 21120

#Unit 12. Applied Biology