SIZE POLYMORPHISM OF THE X-CHROMOSOME DUE TO ATTACHMENT OF A B-CHROMOSOME IN THE MEDFLY, CERATITIS-CAPITATA (WIED)

A chromosomal polymorphism affecting the length of the long arm of the X-chromosome, along with the presence of a B-chromosome is reported i n a laboratory population of Ceratitis capitata. The observed B-chromo some is small, heterochromatic and telocentric. It was found, in both sexes, in somatic cells (cerebral ganglia tissue) as a free chromosome , or terminally attached to the long arm of the X-chromosome, giving t he appearance of a larger X chromosome, Males transmit both free B and large X-chromosomes to their progeny. Females only transmit large X t o their progeny, at a higher rate than they do the standard X, suggest ing either a differential utilization of the ovules carrying the large X or a preferential coorientation during the first meiotic division.