Figure 1.
Figure 1.

Illustration of interpretation of evidence for chimerism. The histogram shows the frequency of relative intensity values for allele 1 using only hair-derived DNA from the combined Holstein and Jersey populations for 1 SNP, Hapmap51593-BTA-42524. The relative intensity values cluster for the 3 genotypes, TT, CT, and CC. Solid blue lines depict the range of relative intensity values observed for each genotype. Allele 1 (allele 2) homozygotes could logically have relative intensity scores as great as 1 (as low as 0) for allele 1, thus the maximum (minimum) acceptable value for relative frequency of allele 1 (allele 2) was extended to 1 (0) (gray line). Representative chimeric (32382) and nonchimeric (32383) twins are indicated by red squares. Blood-derived DNA relative intensity value for 32382 is inconsistent with its hair-derived DNA genotype of TC, indicating chimerism. In contrast, blood-derived relative intensity value for 32383 is consistent with its hair-derived DNA genotype of TT, and its classification was nonchimeric.

 


Figure 2.
Figure 2.

Distribution of genotype data by relative intensity value. Jersey and Holstein breeds were combined for 17 SNP, as differences in mean relative intensity between breeds for each genotype were not significant (P > 0.05). Distribution differed (P < 0.05) for 2 SNP (ARS-BFGL-NGS-89490 and BTB-01133499), and they were not combined (depicted separately). The x axis indicates the hair-derived DNA relative intensity value, and the y axis is the percentage of samples with a given relative intensity value. SNP BTB-00921095 was discarded as no heterozygote genotypes were observed, suggesting assay failure.

 


Figure 3.
Figure 3.

Distribution of the number of SNP that are informative across twinsets. The 10 twinsets that have 0 informative SNP correspond to 3 Jersey and 7 Holstein twinsets presumed to be monozygotic. The number of informative SNP per twinset ranges from 2 to 17 out of a possible 19.

 


Figure 4.
Figure 4.

Distribution of percentage of informative SNP determined to be chimeric for each dizygotic twin for the Holstein and Jersey populations combined. Chimerism was determined using the relative intensity value for allele 1 derived from genotyping blood-derived DNA in comparison.

 


Figure 5.
Figure 5.

Relationship between the proportions of co-twin influences between members of a twinset. Each point represents a twinset, with the x axis corresponding to the twin with greater leukochimerism and the y axis corresponding to the twin with lesser leukochimerism. An arbitrary threshold (45% co-twin influence in the twin with greater leukochimerism) was used to divide the data into low (black diamonds) and high (blue circles) relative levels of leukochimerism. Twinsets with lesser leukochimerism did not exhibit a significant (P > 0.05) relationship between co-twin influences in members of the twinset (solid black line). In contrast, twinsets with greater leukochimerism had a strong inverse relationship between co-twin influences for members of the twinset (P < 0.001; solid blue line).