When an open reading frame (orf) is identified, it may not actually correspond to the amino acid sequence of any polypeptide in the cell. why not? (select all that apply.)
a. the dna may not be transcribed into rna.
b. the amino acid sequence may not match any known sequence.
c. the orf could be due to chance.
d. it may contain one or more stop codons in the middle.

The correct answers are options a and c.

Explanation:

In certain cases, when an ORF or an open reading frame is determined, it may not actually correspond to the amino acid sequence of any polypeptide in the cell. This may have occurred as the ORF could have taken place by chance, or the DNA may not have got transcribed into RNA at all.  

Some of the ORFs are found by mere chance, the ORFs, which codes for sixty amino acids can take place frequently by chance, that is, 5 percent according to the Poisson model.  

Even in some of the cases, the ORFs, which codes for about 150 amino acids could have also taken place by chance in some of the bigger genomes, in which the percentage of occurrence is about 0.05 percent. Also, in some of the circumstances, it can take place as DNA does not get transcribed at all into RNA.  

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