Experiments were designed to investigate the effect of homozygous deletions upon the frequency and the average length of heterozygous regions in bacteriophage T4D. A long deletion, rdf41, which covers at least the whole rII region, was found to increase the heterozygosity for r48, while no increase was observed when a short deletion was employed. The long deletion was found to increase the average length of amber-HETs by a length approximately the size of the rII region.
A drastic reduction in average HET length was found in FUDR crosses homozygous for the long deletion rdf41, indicating that the type of HET that does increase in FUDR is very short.
In the cross with no deletion in either parent, premature lysis HETs were found to be much longer than normal lysis HETs. Assuming that redundancy HETs are long compared to heteroduplex HETs this result indicates that redundancy HETs are made earlier in the latent period than heteroduplex HETs. A fluctuation in HET frequencies was found for different markers, especially in FUDR.
About half of all HETs, both in normal crosses and in FUDR crosses, was found to be parental for outside markers.
In non-FUDR crosses, polarized segregation was shown by 12 out of 27 multi-marker HETs after normal lysis and 5 out of 22 multi-marker HETs after premature lysis. In FUDR crosses, 24 out of 77 multi-marker HETs showed polarity.