1.)what do the differently written term 'Cry' and 'cry' represent ?
2.) how does the gene of an enzyme a-galactosidase can be used as selectable marker? how is it better then other traditional marker like antibiotic resistance genes?
@Nivedita: For first part part of your question you may refer to the answer provided by your friend.
β galactosidase acts as a selectable marker as it can be used for insertional inactivation which leads to selection of recombinant DNA. Recombinant colonies are white in colour because of inactivation of β galactosidase while non recombinants are blue in colour. Colour makes it easy to distinguish between recombinant and non recombinant cells.
Antibiotic resistance method requires a lot of screening and since number of recombinants is very low, this process becomes very tedious as there is no colour difference and naked eye cannot differentiate between recombinant and non recombinant DNA.
@Archana: Good! Keep it up.