The Hardy-Weinberg principle asserts that allele frequencies in a population remain constant; for example, if 50% of people have blue eyes, then each successive generation will continue to have 50% of people with blue eyes as long as certain assumptions are met. The Hardy-Weinberg equilibrium assumes that within a population random mating occurs, no migration occurs, no mutations occur, no natural selection occurs, and the population is sufficiently large. If any of these assumptions are not met, the allele frequencies of the population will change, causing the population to evolve. For this question, all of the answer choices except "Random mutations" (remember there must be no mutations) are required assumptions for the Hardy-Weinberg equilibrium to be in effect.

This is a Hardy-Weinberg Equilibrium problem. The question stem gives you the prevalence of the dominant allele, 0.6. The prevalence of the dominant allele and the prevalence of the recessive allele must always add together to equal 1:

So, the prevalence of the recessive allele must be 0.4:

The prevalence of the recessive phenotype is equal to the prevalence of the recessive allele squared:

In this case, black coat color is a recessive trait, so the prevalence of this recessive phenotype is equal to the prevalence of the recessive allele squared, or 0.16.

Let's say that the frequency of the dominant allele ("A") is represented by p, and the frequency of the recessive allele ("a") is represented by q. Since these are the only two alleles for the trait, their frequencies must add up to one:

The frequency of the AA genotype is , the frequency of the Aa genotype is , and the frequency of the aa genotype is .

Hardy-Weinberg equilibrium assumes the absence of external forces like genetic drift and selective pressure. In other words, it is based on the assumption that allele frequency is relatively constant across generations.

All three given properties contribute to water's motion up the xylem of a plant, as transpiration brings up the water through evaporation due to heat and sunlight. However, as water is a polar molecule and has properties of cohesion and adhesion, molecules of water stick together and resist forces that would push the water out of the plant. This dynamic is referred to as the cohesion-tension theory.

The correct answer is "xylem . . . phloem." Water and nutrients move from the roots through plant stem to the rest of the plant. Stems are made from three tissues: ground, dermal, and vascular. Vascular tissue is primarily divided into xylem, which primarily transports water, and phloem, which primarily transports sugars.

The correct answer is hypothalamus. The hypothalamus is made of nervous tissue and is a part of all vertebrate brains, placing it as part of the nervous system. It also secretes a number of hormones that directly affect the pituitary gland, affecting a large number of bodily functions. In this way, the hypothalamus connects the nervous and endocrine systems and is part of both of them.

Lipase and trypsin are enzymes secreted by the pancreas into the duodenum of the small intestine. These enzymes aid in the digestion of food. Salivary glands produce amylase in order to begin digestion in the mouth and the stomach aids in digestion primarily via stomach acid . 

The correct answer is GABA. GABA is the primary inhibitor used to lower the activity of cells in the human central nervous system. Glutamate, serotonin, and dopamine usually increase the activity of cells, and acetylcholine can increase or decrease cell activity depending on what cell receptor is interacting with the acetylcholine.

This question examines your ability to read a graph correctly. The optimal concentration of YTSS for bacterial growth is the concentration of YTSS in the dish that allowed for the most bacterial growth in 24 hours. Looking across the vertical bars, which represent bacterial growth in millimeters, the dish that had the highest amount of bacterial growth was the dish containing a concentration of  YTSS with ~54mm. And so the optimal concentration of YTSS for bacterial growth must be  YTSS.

The correct answer is the "nucleus." Prokaryotes generally do not have membrane-enclosed organelles, and they do not have a nucleus. Plasmids are found in all prokaryotes, as well as in fungi. The other structures are found in both prokaryotes and eukaryotes.