Alarge population of laboratory animals has been allowed to breed randomly for a number of generations. after several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. the rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.

what is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?

a) the population is undergoing genetic drift.
b) the two phenotypes are about equally adaptive under laboratory conditions.
c) the genotype aa is lethal.
d) there has been a high rate of mutation of allele a to allele a.
e) there has been sexual selection favoring allele a.

b) The two phenotypes are about equally adaptive under laboratory conditions.

Explanation:

According to the given information, the frequency of homozygous recessive genotype and the recessive allele is not changed over generations and is maintained at a constant level. A population maintains allele frequencies over generations without any changes when the environment is not changing and the existing allele frequencies are beneficial in terms of survival and reproductive success of the individuals.

In the given breeding program, both the recessive and dominant genotypes should impart beneficial adaptive traits to the organisms resulting in no change in their frequencies over several generations.

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.