The Differential Activity of X Chromosomes in Mammals

Distance, Diameter Diameter Ratio Hind legs Anal lobes 

Linear dimensions are given in microns and are based on 50 measurements. Spines from anal lobes with three spines were not measured 

In some tissues of the male, deheterochromatization occurs during a certain period of development. It is precisely these tissues which do not develop normally if the individual has either an irradiated paternal genome or the genome of another species. Decondensation does not take place in all cells and, as a result, these tissues are functionally mosaics. 

To explain the mechanism of paternal genome inactivation in Pseudococcus, Nur (1973) postulated that females produce two types of eggs those with a compound that induces heterochromatization of the paternal chromosomes and those without this compound. After fertilization the first type of egg develops into males and the second into females. 

As mentioned previously, the hypothesis of differential activity of X chromosomes was developed by Lyon (1961) and was used to explain gene dosage compensation in mammals. The inactivation of one X chromosome in XX females is accompanied by the heterochromatization of this chromosome and the subsequent formation of the heteropycnotic body. According to this hypothesis (1) the hetero- 

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