Simultaneous loss of two knobbed chromosomes induced by B chromosomes in maize

摘要

It was analyzed the interaction of B chromosomes with large knobs on chromosomes 3 and 9 in maize (high loss phenomenon), determining the frequency of concomitant breaks on these chromosomes, scoring for endosperm markers. Simultaneous loss of chromosomes 3 and 9 had a value 2.2 times higher than that expected if considering independent events. It seems that breaks induced by B chromosomes are clustered in specific spores. From the four different types of sperm nuclei derived from breakage of the two bridges of knobbed chromosomes 3 and 9, at the same or opposite sides of the equatorial plate, at the second microspore mitosis, only one of them can be correctly scored in the endosperm as doudle loss. Two are scored as single loss, since one translocated chromosome goes to the endosperm and the other to the embryo and one sperm nucleus has two normal chromosomes in the endosperm hence the dicentric chromosome goes to the embryo. So, when we score for markers in the endosperm, the observed frequency of simultaneous loss is only one fourth the actual frequency. [References: 11]