LINKAGE ANALYSIS OF FAMILIES WITH HEREDITARY RETINOBLASTOMA - NONPENETRANCE OF MUTATION, REVEALED BY COMBINED USE OF MARKERS WITHIN AND FLANKING THE RBI GENE

Nonpenetrance of the inherited mutation responsible for retinoblastoma has been reported. By DNA analysis in families with hereditary retinoblastoma, it is possible to identify healthy individuals in whom the mutation is nonpenetrant. This requires the use of DNA markers both within and flanking the retinoblastoma gene. We have analyzed the segregation of several markers in 19 families (69 meioses) with hereditary retinoblastoma. In two families a carrier was identified who showed nonpenetrance of the mutation predisposing to retinoblastoma. The intragenic markers were informative in 15 pedigrees. The use of flanking markers from the same chromosomal region caused an increase of the number of informative families to 18. No crossing-over within the gene was observed. In one family an inherited deletion involving one of the RB1 alleles was detected. Our findings emphasize the use of a combination of both intragenic and flanking markers to obtain both the highest reliability of carrier detection in families with hereditary retinoblastoma and an accurate estimate of the frequency of nonpenetrance

A Third, Remarkably Small, Tribosphenic Mammal from the Mesozoic of Australia

A third species of tribosphenic mammal is nowknown from Australia. Owing to the fragmentary nature ofthe two specimens on which this new, diminutive species isbased, its affinities within the tribosphenic Mammalia areuncertain. When better known, they could well prove tobelong to the Ausktribosphenidae. In estimated body mass,2 g, the new species is amongst the smallest mammalsknow