The unpaired X chromosome of Locusta migratoria males is facultatively heterochromatic in the spermatocytes and early spermatids, showing an alternating cycle of positive-negative-positive heteropycnosis. Discrimination between facultative heterochromatin and euchromatin was made using a modification of the Feulgen reaction. It was found that the differential stainability of the DNA of the X chromosome is correlated with the electron opacity of its chromatin. The corresponding differential stainability and electron opacity should reflect differences in protein content or in spatial rearrangement since the amount of DNA in the X chromosome that is transmitted by the spermatozoa to the next generation should remain constant.

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