An isolated colony on a selective medium is not considered a pure culture because inhibited organisms might be masked by the colonies. This statement is true.
On the basis of their constitution or usage, culture media can be classified into various groups; these include defined, complex, selective, as well as enrichment medium.
A selective medium consists of dyes or noxious substances/chemicals which inhibit the growth of specific microorganisms but promote the growth of other microbes.
A pure culture is a laboratory culture which contains a single species of microorganism. It is free from other microorganisms.
Since selective media affects the growth of distinct organisms differently, therefore, an isolated colony formed in such type of medium is not considered a pure culture.
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Lyases
Lyases are class of enzymes that catalyzes reactions involving the formation of double bonds.
Lyases are class of enzymes that catalyzes the joining of C-C ( carbon to carbon), C-O (carbon to oxygen), and C-N (carbon to nitrogen) bonds by hydrolysis or oxidation. These bonds are usually held by the process of elimination which leads to the formation of new double bonds or cyclical molecules. Examples of lyases include; aldolase and adenylate cyclase.
It would be 75% because that is 3/4, the chances of dominant offspring.