Fossils are the remains and traces of past life that have been preserved in the Earth's crust. What type of fossils is most important in supporting the principle of evolution? Explain your answer and give examples.
What will be an ideal response?
Transitional fossils are important evidence for evolution, as they allow us to trace the descent of organisms. Transitional fossils bear a resemblance to two groups that in the present are classified separately. They often represent the intermediate evolutionary forms of life in transition from one type to another, or a common ancestor of these types. An example of a transitional fossil is Archaeopteryx, which is an intermediate between dinosaurs and birds. A series of transitional fossils allow scientists to document the origin of new forms of life. In addition to Archaeopteryx, intermediate fossils such as Sinornis, Confuciusornis, and Iberomesornis, possess various characteristics of birds and reptiles that show how the species of today evolved. Ambulocetusnatans is the terrestrial ancestor of modern day whales. The name, which literally means, "walking whale that swims" is appropriate, as this organism had webbed feet on its limbs that allowed it to walk and swim and had the skull and teeth of early whales. Even younger fossils were found of additional intermediate forms, such as Pakecetus and Rodhocetus, that have allowed us to trace the evolution of the whale.
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A small number of cell surface receptors can ultimately generate a large intracellular response due to activation of kinase cascades. This is referred to as:
A. signal amplification. B. signal transduction. C. signal dampening. D. signal activation.
While it is very difficult to find fossils of the earliest cells, there are some probable early cell characteristics. Four of the five answers represent possible traits that the first cells may have had. Select the exception:
a. prokaryotic b. autotroph c. aerobic d. anerobic e. hetrotroph
When cichlids were present, what was the main selection factor affecting the average number of spots on male guppies?
a. natural selection for a reduction in spot number in order to avoid predation b. natural selection for an increase in spot number to enhance camouflage ability c. natural selection for a reduction in spot number to enhance attractiveness tofemales d. natural selection for an increase in spot number to enhance attractiveness tofemales
Of the following mutations, which are likely to cause cell-cycle arrest? If you predict a cell-cycle arrest, indicate whether the cell will arrest in early G1, late G1, or G2. Explain your answers
A. a mutation in a gene encoding a cell-surface mitogen receptor that makes the receptor active even in the absence of the mitogen B. a mutation that destroyed the kinase activity of S-Cdk C. a mutation that allowed G1-Cdk to be active independently of its phosphorylation status D. a mutation that removed the phosphorylation sites on the Rb protein E. a mutation that inhibited the activity of Rb