<span>The trait that is ancestral to all chordates is the presence of a notochord...the others are gill slits and nerve chord</span>
As for this problem, the most probable answer and the most likely answer for this one would be D. the effect of pesticides on organisms in the environment.
A toxicologist would only study about chemicals and their effect on organisms in the environment. Pesticides are chemicals made to combat organisms that aren't wanted particular parts of the environment such as crops and rice field. These pesticides don't just affect those organisms that are targeted, but even the users and other organisms that may have come in contact with pesticides.
It is the fraction of all chromosomes in the population that carry that allele.
The answer is "bb" because a gene must have alleles that are both recessive in order for the recessive trsit to take over.
