Why are identical twins ideal
for studying the impact of the
environment on phenotypes?

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i. e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).

The offspring of two different species

Examine the pedigree below. if curly hair (c) is a dominant trait, what are the genotypes of the parents in the pedigree? a. one parent is homozygous for the curly hair trait (cc), and the other parent is homozygous for non-curly hair (cc). b. one parent is heterozygous (cc) for the curly hair trait, and the other parent is homozygous for the curly hair trait (cc). c. both parents are homozygous (cc) for the curly hair trait. d. both parents are heterozygous (cc) for the curly hair trait.