Determination of the optimal tissue source and number of microsatellites for detection of zygotic origin of cattle twins

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Abstract
Twenty pairs of cattle twins were genotyped for 3 to 12 microsatellites each using semen, blood, milk and hair roots. Chimaerism was recognized in 19 pairs by discrepancies in microsatellite analysis from milk and blood as opposed to semen and hair, or by detection of more than 2 alleles per genotype from milk and blood. Chimaerism of 2, 3 or 4 alleles was demonstrated in genotypes of twins from blood as compared to 1 or 2 alleles only from hair. The appearance of predominant bands in genotypes from blood or milk representing alleles of only one of the co‐twins was not consistent among the different microsatellites for the same twins. No evidence for germ cell chimaerism was found in semen of dizygotic male twins although our PCR system could detect cell mixes as small as a 1:100 ratio. Genotyping from either hair or semen for 4 microsatellites are sufficient to confirm zygotic origin of twins at .98 accuracy. Researchers should be aware of the possibility of erroneous genotyping when analyzing DNA from twins derived from blood or milk and the potential of chimaerism as an experimental model to study different immunological characteristics of cattle co‐twins.