SPECIFIC CHROMOMERES ON THE CHICKEN-W LAMPBRUSH CHROMOSOME CONTAIN SPECIFIC REPETITIVE DNA-SEQUENCE FAMILIES

Chromomeres 1 and 3 of the chicken W lampbrush chromosome contain most of the EcoRI and Xhol repeat sequence families respectively. These ch romomeres were stained with DAPI and their sizes relative to other W c hromomeres were observed. Their relative contents of EcoRI and Xhol re peats were determined using fluorescence in situ hybridization with ge nomic probes for each of the two repeat families. There were two types of W chromosome in the chickens (White Leghorn and Rhode Island Red) used in this study with respect to the amount of EcoRI repeat. A high- copy-number type has about 4000 copies of the 1.2-kb repeat per genome and shows a large fluorescence signal on W chromomere 1. A low-copy-n umber type has about 700 copies per genome and does not have a detecta ble chromomere 1 on W chromosome, nor does it show FISH labelling in t he region normally occupied by chromomere 1. The genome of Fayoumi chi ckens has about one-sixth the amount of the Xhol sequence family of Wh ite Leghorns. W lampbrush chromomere 3 is much smaller and its FISH la belling with the Xhol probe is much weaker in Fayoumis than in White L eghorns. These results demonstrate that in the chicken W chromosome, s pecific chomomeres are occupied by specific DNA repeat sequence famili es.