Chromosome Organization and Heterochromatin Elimination in Parascaris

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Abstract
A cytological analysis by modern banding techniques of gonial metaphases in two Parascaris forms that have been considered varieties but now seem to be two species [P. univalens (karyotype 2n = 2) and P. equorum (karyotype 2n = 4)] reveals a different chromosome organization in each. Parascaris univalens chromosomes contain only terminal heterochromatin, while P. equorum chromosomes also contain intercalary heterochromatin. In the somatic cells of both species during early embryogenesis, chromatin diminution occurs in and consists of the elimination of all heterochromatin independent of its localization in the chromosomes.