Question

A sequence, TTGCTGCGCTAAA, may be methylated at one or more of the cytosine residues. After bisulfite sequencing, the following results are obtained:

Bisulfite treated: TTGCTGTGCTAAA
Untreated: TTGCTGCGCTAAA
Write the sequences showing the methylated cytosines as Cᴹe.

Answer 1

Methylated cytosines in the DNA sequence are identified as the ones that remain unchanged after bisulfite treatment. Comparing the treated and untreated sequences, we pinpoint the methylated cytosine at one CG site. The sequence with methylated cytosines labeled as Cᴇe is TTGCTGCᴇeGCTAAA.

Step-by-step explanation:

The sequence you provided underwent bisulfite treatment, which converts unmethylated cytosines to uracils (later read as thymines after PCR), but leaves methylated cytosines unchanged. Comparing the bisulfite treated DNA sequence (TTGCTGTGCTAAA) to the untreated sequence (TTGCTGCGCTAAA), we can find where the methylated cytosines are. Methylated cytosines are the ones that did not change after bisulfite treatment.

In the untreated DNA sequence, when we locate a cytosine followed by guanine (CG), we need to see if these cytosines remain the same in the treated sequence to confirm methylation. The sequence showing the methylated cytosines as Cᴇe would be: TTGCTGCᴇeGCTAAA.