The effects of X-rays on the chromosomes of locust embryos

The structure and frequency of chromatid interchange types in C-metaphase cells of embryos of Schistocerca gregaria are described at the first mitosis following irradiation at the G ₂ stage of interphase. The relationship between the different interchange types and the organisation of the interphase nucleus is discussed. It is concluded that most chromatid interchanges are induced between polarised chromosomes though the occurrence of loops and to a lesser extent of terminal overlapping may subsequently modify the appearance of these aberrations at metaphase.