Familial retinoblastoma: segregation of chromosome 13 in four families.

Fluorescent markers on chromosome 13 have been used to study familial retinoblastoma. One family showed concordant segregation of a particular chromosome 13 and retinoblastoma from the affected parent to the affected children. In three other families, segregation was discordant. Meiotic crossing over with recombination is proposed as the explanation.