DOMINANT LETHALITY AND CORRELATED CHROMOSOME EFFECTS IN HABROBRACON EGGS X-RAYED IN DIPLOTENE AND IN LATE METAPHASE I

Abstract

Unlaid Habrobracon eggs x-rayed in diplotene (lethal dose about 45,000 r) and allowed to develop parthenogenetically, show fragments, bridges or both in division I; either or both in division II. Bridges in division I may be permanent. Unlaid eggs x-rayed in late metaphase I (lethal dose about 1,400 r) show, fragments but no bridges in division I; bridges, fragments or both in division II. An explanation of difference in cytological effects of x-rays on these stages and of the differences between them in sensitivity and in nature of survival curves is attempted through comparison with studies on forms with larger chromosomes.