Origin and significance of centric fusions in domestic sheep.

The karyotypes of 731 sheep of various breeds were studied and considered in association with previous chromosome studies of domestic sheep. A high incidence of the t2 trnslocation was found in two pedigree flocks of New Zealand Romney sheep. One of these flocks was established over 100 years ago and it is suggested that this translocation originated in the Romney Marsh breed of sheep in England. A naturally occurring double translocation heterozygote 52t1t2 was reported for the first time. A further flock of sheep of the Perendale breed was found with a high incidence of dicentric chromosome fusion that was identified as the t3 translocation. The apparently common occurrence of chromosome polymorphism, due to centric fusions, in domestic sheep is discussed in relation to karyotype evolution among both domestic and wild sheep.