4.
if the offspring of a dihybrid cross have a 9: 3: 3: 1 phenotypic ratio, what must be true of the parents’ genotypes?

both parents are heterozygous for only one trait.

both parents express the dominant trait.

both parents express the recessive trait.

both parents are heterozygous for both traits.

The observations of hooke and van leeuwenhoek documenting the existence of microscopic cells formed the basis of what important theory? a. the cell theory stating that all living things are composed of cellsb. the theory of spontaneous generation, which held that life forms could arise spontaneouslyc. the theory of chemotherapy, or use of antimicrobials to destroy pathogenic organismsd. the germ theory of disease and causative agents

Most animal cells membranes have proteins that pump ions out of the cell and potassium ions into the cell

Which statement best describes how the loudness of the sound affects the high-pressure region created by the sound wave? a. a louder sound has no effect on the pressure created. b. a louder sound means a high-pressure region that is higher. c. a louder sound means a high-pressure region that is not as high.