Somatic crossing over as a cause of chromosome multivalents in cotton

TitleSomatic crossing over as a cause of chromosome multivalents in cotton
Publication TypeJournal Article
Year of Publication1974
JournalJournal of Heredity
Start Page3
Date Published1974

Occasional somatic pairing of homologous chromosomes was observed in some plants and animals shortly after the turn of the century. There have been many other examples of pairing in succeeding years; where genetic markers were available for analysis, theory have provided evidence of somatic recombination. Stern19 observed single and twin spots of homozygous somatic tissue on wild-type background of Drosophilia heterozygous for specific marker genes. He established that somatic crossing over occurred in the four-strand stage and was genetically equivalent to meiotic crossing over. Jones12 suggested that spotting observed in corn tissues could be explained by somatic paring and crossing over. Vig22 reported genetic evidence of somatic crossing over as a course of twin spot in soybeans, heterozygous for incompletely doming gene Y11 for foliage color. He noted increased frequency of twin spots after treatment with chemicals known to allow rejoining of chromosomes. We2 observed twin spots in the leaves of homozygous cotton plants and considered somatic crossing over between homoeologous chromosomes as a more plausible explanations than somatic nondisjunction. In the early 1950's, geneticists working with several genera of imperfect fungi reported genetic recombination, concluding that somatic pairing of homologous chromosomes must occur.  Westergaard concluded "that somatic crossing over that results in genetic recombination can only occur in cells having genetic recombination can only occur in cell having somatic pairing" (see Brown5 p,61). Gruberg9 stated "the cumulative weight of evidence makes a strong case for the existence of somatic crossing over in laboratory rodents." Holliday11 determined that somatic pairing of homologues occurs during interphase of the same time DNA is replicated.