Ochre and amber are two distinct nonsense mutations. Before the genetic code was worked out, Sydney Brenner, Anthony O. Stretton, and Samuel Kaplan applied different types of mutagens to bacteriophages in an attempt to determine the bases present in the codons responsible for amber and ochre mutations. They knew that the ochre and amber mutations were suppressed by different types of suppressor mutations, which demonstrated that each is a different stop codon. They obtained the following results: (1) A single-base substitution could convert an ochre mutation into an amber mutation. (2) Hydroxylamine induced both ochre and amber mutations in wildtype phages. (3) 2-Aminopurine caused ochre to mutate to amber. (4) Hydroxylamine did not cause ochre to mutate to amber. These data do not allow the complete nucleotide sequence of the amber and ochre codons to be worked out, but they do provide some information about the bases found in the nonsense mutations. a. What conclusions about the bases found in the codons of amber and ochre mutations can be made from these observations? b. Of the three nonsense codons (UAA, UAG, UGA), which represents the ochre mutation?
Ochre and amber are two distinct nonsense mutations. Before the
genetic code was worked out, Sydney Brenner, Anthony O. Stretton, and
Samuel Kaplan applied different types of mutagens to bacteriophages in
an attempt to determine the bases present in the codons responsible for
amber and ochre mutations. They knew that the ochre and amber
mutations were suppressed by different types of suppressor mutations,
which demonstrated that each is a different stop codon. They obtained
the following results:
(1) A single-base substitution could convert an ochre mutation into an
amber mutation.
(2) Hydroxylamine induced both ochre and amber mutations in wildtype
phages.
(3) 2-Aminopurine caused ochre to mutate to amber.
(4) Hydroxylamine did not cause ochre to mutate to amber.
These data do not allow the complete
and ochre codons to be worked out, but they do provide some
information about the bases found in the nonsense mutations.
a. What conclusions about the bases found in the codons of amber and
ochre mutations can be made from these observations?
b. Of the three nonsense codons (UAA, UAG, UGA), which represents the
ochre mutation?
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