A genetic linkage map of 27 markers on human chromosome 21

A graphical representation of genetic and physical maps: the Marey map

A novel, simultaneous, visual representation of sex-specific genetic maps and physical maps is introduced. Such maps, called Marey maps, provide direct comparisons of multiple genetic maps and elucidate the relationship of recombination frequency to physical distance.

A 48,XXY,+21 Down syndrome patient with additional paternal X and maternal 21

The origin of meiotic nondisjunction of the extra chromosomes X and 21 was studied in a patient with the karyotype 48,XXY,+21 using DNA polymorphisms. The extra chromosome X was the result of paternal first meiotic nondisjunction of X and Y. The extra chromosome 21 was derived from the mother. The meiotic error in the mother most probably occurred in meiosis II. Thus, this is a combination caused by the chance occurrence of two independent events.