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This study evaluated the applicability of droplet digital PCR (ddPCR) as a tool for maize zygosity determination using quantitative real-time PCR (qPCR) as a reference technology. Quantitative real-time PCR is commonly used to determine transgene copy number or GMO zygosity characterization. However, its effectiveness is based on identical reaction efficiencies for the transgene and the endogenous reference gene. Additionally, a calibrator sample should be utilized for accuracy. Droplet digital PCR is a DNA molecule counting technique that directly counts the absolute number of target and reference DNA molecules in a sample, independent of assay efficiency or external calibrators. The zygosity of the transgene can be easily determined using the ratio of the quantity of the target gene to the reference single copy endogenous gene. In this study, both the qPCR and ddPCR methods were used to determine insect-resistant transgenic maize IE034 zygosity. Both methods performed well, but the ddPCR method was more convenient because of its absolute quantification property.

Simple heritability estimators of continuous as well as discrete traits from twin data are known to overestimate the degree of genetic determination of the measured traits for several reasons. Errors of zygosity determination will, however, underestimate the true heritability. The bias due to wrong assignment of dizygous twin pairs into monozygous type is evaluated here, and the results indicate that this negative bias has a compensatory effect on the estimate of the degree of genetic determination when other factors of similarity between twin pairs are taken into account. It is shown that when an estimate of zygosity error is available, the bias due to this factor can be evaluated quantitatively, and hence the adjustment for zygosity error can be incorporated in the estimation of the degree of genetic determination of a trait.

This study is the first to examine the genetic risk in a breast cancer-prone family wherein two of three triplet sisters and their mother manifested breast cancer. The unaffected triplet, the proband, was found to be monozygotic with her deceased sister through DNA testing of tumor blocks and dizygotic to her living affected sister. Genetic counseling implications are discussed.

Data from individual interviews, blood grouping analyses, and ratings of photographs of a large sample of adolescent twins were examined in order to assess the accuracy of zygosity determination by alternate methods. Although the accuracy of the twins themselves and of the raters was above chance, it was not sufficiently high to justify diagnosis by these methods rather than by blood grouping analyses.

The perinatal death of one twin may be as great a loss to the mother as that of a single baby. This is rarely appreciated. The experiences and needs of a sample of 14 bereaved mothers of multiple births (12 twin, 2 triplet) obtained through the Twins and Multiple Births Association, were explored by semi-structured questionnaires. Results - All mothers perceived the survivor as a twin. 6 had feelings of rejection towards this child initially. Others overprotected and continued to have unjustified anxiety. The initial difficulties of simultaneously celebrating a birth and mourning a death were revived at anniversaries. All mothers had wanted to talk about the dead baby but many had been discouraged and made to feel guilty about their grief. Suppression of grief sometimes led to unresolved mourning. Some felt they had been given inadequate information and all wanted to know the twins’ zygosity. The fear of a fantasy twin was expressed by some who had no tangible reminders. Suggestions for future professional practice - Acknowledgement of the importance of the dead baby. Encouragement of mother to talk about him. Provision of counselling facilities. Provision of ultrasound scan to reduce fear of fantasy twin; of photographs of babies including, with liveborns, of both together, of zygosity determination.