Origin of repeats in Drosophila chromosomes

Abstract

The salivary gland chromosome analysis of repeats (Rp''s) induced by feeding of larvae with formaldehyde, and the frequencies of different types of Rp, indicate that most or all Rp''s result from the breaks which appear in two sister chromatids at the same level (isochromatid breaks). This type of break may arise most readily from potential chromosome breaks, which open in sister chromatids. This suggestion is strongly supported by the fact that formaldehyde which produces mainly potential breaks yields a high frequency of Rp''s, while X-rays yield very few of both.