The answer is environmental stress
Plasmids, they are mostly found in bacterial cells and they r the cause of antibiotic resistance in bacteries :)
Remember for a di hybrid cross with two completely heterozygous parents, the phenotypic ratio will always be 9:3:3:1
9 will always display both dominant traits, black and rough hair. 3 will display black hair and smooth hair and 3 will display not black hair and rough hair and 1 will display both receive traits
