Sex mosaics or gynandromorphs

• In some  insects sometimes one part of the body is male, the other part female producing sex mosaics known as gynandromorphs or gynanders. These have been studied most thoroughly
  in Drosophila which has no sex hormones so that tissues develop autonomously. 
• The sexual phenotype is determined by the number of X chromosomes against sets of autosomes. If during mitosis in early embryogenesis there is nondisjunction between the two X chromosomes, some cells will have XX, others XO constitution. 
• The descendents of XX containing cells will result in the development of female tissues while descendents of XO cells will produce male tissues. The resulting individual will be a spectacular mosaic. Gynandromorphs are usually bilateral with one side of the body male, the other side female. 
• There are irregular gynandromorphs also in which the proportions of male to female tissues are variable depending upon the time and stage of embryo development when XX nondisjunction took place.
  Sex mosaics are sometimes mistaken for intersexes. In a gynandromorph the boundary
  between male and female regions is always sharp and distinct, whereas in intersexes, all parts of the body may have a mixture of male and female characteristics showing a condition intermediate between maleness and femaleness.
• Sex mosaicism occurs in humans also. Chromosome preparations from peripheral blood
  may show XO/XX or XO/XXY cells frequently observed in Turner’s and Klinefelter’s syndromes.
•  As in Drosophila, if there is nondisjunction of two X chromosomes during early stages of embryo development, it results in mosaicism.