The expression "chemical modifications, such as methyl groups" appears not accurate enough. For modification is an action of modifying, so "such as methyl groups" is not a case of modification.
Should it be written as "such as methylation in which methyl groups tag DNA"? (Sorry here you need some knowledge about methylation)
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Marks of life
The epigenetic clock relies on the body’s epigenome, which comprises chemical modifications, such as methyl groups, that tag DNA. The pattern of these tags changes during the course of life, and tracks a person’s biological age, which can lag behind or exceed chronological age.
Source: Nature 05 SEPTEMBER 2019
First hint that body’s ‘biological age’ can be reversed
Should it be written as "such as methylation in which methyl groups tag DNA"? (Sorry here you need some knowledge about methylation)
**************************************
Marks of life
The epigenetic clock relies on the body’s epigenome, which comprises chemical modifications, such as methyl groups, that tag DNA. The pattern of these tags changes during the course of life, and tracks a person’s biological age, which can lag behind or exceed chronological age.
Source: Nature 05 SEPTEMBER 2019
First hint that body’s ‘biological age’ can be reversed