Identification Strategy of Biological Half Sibling Relationship

Abstract

Objective To compare the application value of the likelihood ratio （LR） method and identity by state （IBS） method in the identification involving half sibling relationships， and to provide a reference for the setting of relevant standards for identification of half sibling relationship. Methods （1） Based on the same genetic marker combinations， the reliability of computer simulation method was verified by comparing the distributions of cumulated identity by state score （CIBS） and combined full sibling index in actual cases with the distributions in simulated cases. （2） In different numbers of three genetic marker combinations, the simulation of full sibling, half sibling and unrelated individual pairs, each 1 million pairs, was obtained; the CIBS, as well as the corresponding types of cumulative LR parameters， were calculated. （3） The application value of LR method was compared with that of IBS method， by comparing the best system efficiency provided by LR method and IBS method when genetic markers in different amounts and of different types and accuracy were applied to distinguish the above three relational individual pairs. （4） According to the existing simulation data， the minimum number of genetic markers required to distinguish half siblings from the other two relationships using different types of genetic markers was estimated by curve fitting. Results （1） After the rank sum test， under the premise that the real relationship and the genetic marker combination tested were the same， there was no significant difference between the simulation method and the results obtained in the actual case. （2） In most cases， under the same conditions， the system effectiveness obtained by LR method was greater than that by IBS method. （3） According to the existing data， the number of genetic markers required for full-half siblings and half sibling identification could be obtained by curve fitting when the system effectiveness reached 0.95 or 0.99. Conclusion When distinguishing half sibling from full sibling pairs or unrelated pairs， it is recommended to give preference to the LR method， and estimate the required number of markers according to the identification types and the population data， to ensure the identification effect.

Keywords

• |forensic genetics|sibling relationship|half sibling|likelihood ratio|identity by state|short tandem repeats|single nucleotide polymorphism|microhaplotype