Non-disjunction and chromosome theory of inheritance. The results obtained due to non-disjunction were not expected on the basis of normal segregation patterns. However, these could be easily explained on an assumption that two X-chromosomes in female individual are not disjoining. If such an assumption of non disjunction was correct, XXY female individuals would obtained in the progeny. When exceptional females (white eyed) were cytologically studied, these were found to carry two X-chromosomes and one Y-chromosome (XXY). Such cytological results definitely suggested and, therefore, were put forward as an evidence to show that the genes or Mendelian factors were carried on chromosomes. Therefore, non-disjunction of sex chromosomes (primary and secondary) is considered as a strong evidence in favour of the chromosome theory of inheritance, already discussed earlier in Physical Basis of Heredity 4. The Chromosome Theory of Inheritance.
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