When in U. S, history did pollution start to become an issue? Explain why pollution was not an issue prior to this time period. Answer in at least 3 complete sentences.

Guinea pig coat color is determined by a single gene. the allele for black coat color is dominant to brown. in a cross between twoblack-haired guinea pigs, 20 offspring are born. if both parents were heterozygous, probability would predict that approximately howmany of the 20 offspring would have brown hair?