HUMAN SEX CHROMOSOME ABNORMALITIES IN RELATION TO DNA REPLICATION AND HETEROCHROMATINIZATION

Publisher Website
Google Scholar
Abstract
Tritiated thymidine and autoradlography were utilized to study the sequence of DNA replication in X-chromosomes of the human complement. Five individuals with extra X-chromosomes were found to have one X which replicates with the majority of the complement while all others replicate late. Evidence is presented which indicates that these late-replicating X-chromosomes are heteropycnotic in interphase and their genetic expression is repressed. Two patients with a structurally abnormal X were found to have this chromosome consistently heteropycnotic and late-replicating. These observations are consistent with the "fixed differentiation hypothesis" of X-chromosome behavior.