Final answer:
The new phenotype observed in only a small fraction of cells compared to the growth of strain A and B on complete media can be explained by the process of transformation, which leads to chromosomal abnormalities and rearrangements in cells. The transformed cells, known as cell lines, can grow indefinitely and exhibit a new phenotype.
Step-by-step explanation:
The term phenotype refers to the observable characteristics or traits of an organism, which are influenced by its genes and interactions with the environment. In this context, the question is asking why only a small fraction of cells have a new phenotype compared to the growth of strain A and B on complete media. This can be attributed to the process of transformation, where cells undergo chromosomal abnormalities and rearrangements, leading to the development of a new phenotype. These transformed cells, known as cell lines, can grow indefinitely in culture and do not require solid support for growth.