Question

You performed Cot analysis using genomic DNA samples obtained from a 2 year-old child and a 76 year-old individual. Results of this analysis show that one of the most rapidly reassociating classes of DNA is substantially reduced in the older individual with respect to the 2 year-old. How can you explain this finding? (hint: think about termination of linear DNA replication)

A) The older individual has enhanced DNA replication termination.
B) The older individual experiences slower DNA reassociation due to replication termination.
C) The older individual has faster DNA reassociation due to replication termination.
D) The older individual's DNA reassociation is unaffected by replication termination.

Answer 1

The reduced class of rapidly reassociating DNA in the older individual could be due to an age-related decline in DNA repair mechanisms and telomere shortening, leading to cumulative errors in DNA, especially in highly repetitive sequences.

Step-by-step explanation:

A Cot analysis examines the rate at which denatured DNA reassociates to become double-stranded DNA again. It has been observed that genomic DNA from a 2-year-old child would contain a higher proportion of rapidly reassociating, highly repetitive DNA sequences compared to an older individual. One explanation for the reduced class of rapidly reassociating DNA in the older individual could be related to the cumulative effect of DNA replication errors, which occurs during the termination phase of DNA replication. As we age, our cells' ability to repair DNA declines, potentially resulting in the loss of highly repetitive DNA sequences. Moreover, the erosion of telomeres, the protective caps on the ends of chromosomes, also occurs with each cell division and is not fully compensated as we age. This telomere shortening could affect the integrity of repetitive DNA sequences, making them less likely to be restored and thus, less abundant as detected by a Cot analysis.