Chromosome segregation and expression of rat immunoglobulins in rat/mouse hybrid myelomas

The chromosome segregation of hybrid myelomas from a fusion of rat immunized spleen cells and the mouse myeloma P3-X63-Ag8 has been analysed. Chromosome loss appears to be nonrandom. Most mouse chromosomes are retained. The rat chromosome are preferentially lost but a few--particularly 1-5 and 13--are rarely lost. The specific retention of some rat chromosomes explains the stability of rat Ig expression in mouse-rat hybrids. Correlation of chromosome loss and retention and loss of rat heavy and light chains leads us to propose chromosome 14 as coding for the heavy chain.