Phenotypically normal individuals with an inversion (X) (p22q13) and the recombinant (X), dup q.

Two families are described in which there is an inv(X) (p22q13) which has been transmitted for three generations. In one family (K482), no recombinants have been recovered and the inversion can be traced to a female born in 1839. In the second family (K491), a recombinant (X), dup q, has been recovered in a normal fertile woman. In both families the inverted X appears to be carrying the Xg allele. Despite extensive family studies no common ancestor has been found for the two families. The pattern of DNA synthesis has been studied in those individuals who are karyotypically 46,X,inv(X) (p22q13) and 46,X,rec(X)dup 1, inv(X) (p22q13); the selection of the abnormal as the late synthesizing X chromosome is random in the former and total in the latter. In some cells the two long arms of the recombinant X chromosome showed asynchrony of DNA replication.