ISSN:
1432-0886
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The pattern of labelling over the chromosomes, the chronology of chromosome duplication and the duration of the S and G 2 periods in the leukocytes from 6 normal females and 5 normal males, have been studied by using a combination of pulse and continuous tregtments with thymidine-H3. According to the criteria used to analyse the results it is suggested that the S period begins 15 to 20 hours and finishes 5 to 3 hours before the cells reach the metaphase stage. The S period could be subdivided into the four phases S1 to S4. The first chromosomes to replicate were Nos. 1, 3, 5 and X followed by the Nos. 2, 4 and several chromosomes of groups 6–12, 13–15 and 19–20. Later the pairs 16, 17, 18 and the chromosomes of group 21–22 replicated. Chromosome Y in the male was the last to replicate, beginning its duplication when all the other chromosomes had reached the intermediate S stage. The earliest chromosomes to finish the duplication were Nos. 19, 20 and 21 followed by Nos. 16, 17, 18, 22 and the chromosomes of group 13–15. Afterward and at about the same time the replication of pairs 2, 4, 6, 8, the X and Y chromosomes in the male and one X chromosome in the female concluded. The other X chromosome in the female was the last to end its duplication appearing totally labelled until the final stage of the S period. Replication of the long and medium size chromosomes begins at localised regions, then extends over the total length of the chromosome and at the end of the S stage takes place only in small zones different from those replicating early. Asynchrony between homologous chromosomes was observed at the beginning and at the end of the S period.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00283604
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