In a laboratory experiment of sexually reproducing plants, a certain trait is determined by a single gene. The dominant allele has complete dominance over the recessive allele, resulting in two different phenotypes. Scientists created a new population of this plant by crossing 51 homozygous dominant individuals with 49 homozygous recessive individuals. The following results are from the first five generations of this population: Generation - Number of individuals with dominant trait - Number of individuals with recessive trait - Total number of individuals 1 - 51 - 49 - 100 2 - 285 - 0 - 285 3 - 270 - 90 - 360 4 - 315 - 105 - 420 5 375 - 125 - 500 On the basis of the data, propose an explanation for the phenotypic changes from generations 1 to 3. Do you think this population is in Hardy-Weinberg equilibrium?

The large ground finch obtains food by cracking seeds. what is its short, strong beak an example? a) tendency toward perfection b) adaptation of a species over time c) selective use and disuse of an organ over time d) scarcity of recourses

What is thought to have caused the mass extinction at the end of the cretaceous period?

Experiments in environmental toxicology can sometimes be manipulative experiments in which the researcher actively chooses and manipulates the independent variable. in hunt's study, for example, dosages of bpa were manipulated and the effects were measured. in manipulative studies, the researcher controls all the other variables in the experiment, so any health effects observed in the test subjects can be attributed to differences in the independent variable. in other cases, researchers use natural experiments in which the dependent variable (typically a measure of organism health) is measured under differing contexts that are not manipulated. say, for example, that an accidental chemical spill contaminates five ponds. to determine the possible effects of the toxic chemical on frogs, a researcher could compare the hatching rate of frog eggs laid in those five ponds to the hatching rate of eggs laid in five uncontaminated ponds nearby. this would be an example of a natural experiment because concentrations of the toxic chemical in the ponds were not controlled by the experimenter, but rather resulted from the chemical spill. drag type of experiment on the left to the example of experiment on the right. blood concentrations of bpa in college students are compared to their recent manipulative consumption of canned food items 2. the feeding behavior of fish in streams that receive acidic runoff from strip mines is compared to the feeding behavior of fish in unaffected streams. the deformity rate in baby birds from nests in pesticide-sprayed fields is compared to the deformity rate in birds from nests in unsprayed fields 4 tumor development is compared in mice exposed to five dosages of a known carcinogen in the laboratory foraging activity levels are compared in tadpoles exposed to four concentrations of toxic metals in the laboratory. growth of corn plants is compared in field plots sprayed with three different dosage: s of weed killer 7 bpa concentrations in the urine of people with diabetes are compared to bpa concentrations in the urine of people without diabetes - natural; manipulative