In somatic cell hybridization, human chromosomes are lost preferentially in hybrids with
Human-mouse somatic hybrids preferentially lose human chromosomes because mouse spindle apparatus cannot stably maintain human centromeres leading to gradual elimination during successive divisions whereas mouse chromosomes segregate faithfully due to compatibility with cellular machinery. Initial fusion product contains tetraploid genome complement then human chromosomes shed randomly. Resulting clones retain one to few human chromosomes ideal for correlation mapping of genes to chromosomes. Hybrids with plant or yeast partners incompatible and nonviable making mouse partner standard for human mapping through chromosome loss phenomenon.
Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 5: Human Chromosome Loss in Mouse Hybrids Preferential Elimination