In contrast to vertebrates, there is very little DNA methylation in the genomes of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. Indicate whether you expect each of the following statements to be true (T) or false (F) regarding 5?-CG-3? dinucleotide sequences in the genome. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT.
( ) On average, approximately one dinucleotide out of every 16 in the human genome is a CG dinucleotide.
( ) On average, approximately one dinucleotide out of every 256 in the D. melanogaster genome is a CG dinucleotide.
( ) The proportion of CG dinucleotides in the human genome is more than that of C. elegans.
( ) The proportion of CG dinucleotides in the human genome is more than that expected by chance.

Question

In contrast to vertebrates, there is very little DNA methylation in the genomes of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. Indicate whether you expect each of the following statements to be true (T) or false (F) regarding 5?-CG-3? dinucleotide sequences in the genome. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTT.
(  )	On average, approximately one dinucleotide out of every 16 in the human genome is a CG dinucleotide.
(  )	On average, approximately one dinucleotide out of every 256 in the D. melanogaster genome is a CG dinucleotide.
(  )	The proportion of CG dinucleotides in the human genome is more than that of C. elegans.
(  )	The proportion of CG dinucleotides in the human genome is more than that expected by chance.

Quizplus · Accepted Answer

In a random DNA sequence, one out of every 16 dinucleotides is a CG. However, these dinucleotides are found at a much lower frequency in the human genome, which is probably related to the fact that cytosine methylation at these sites (which has a role in transcription regulation) can be followed by deamination to cause a C-to-T substitution. Consistent with this notion, the CG frequency in D. melanogaster and C. elegans is close to the expected value.

In Contrast to Vertebrates, There Is Very Little DNA Methylation