Chiara Toni

Inferring relationships between pairs of individuals from locus heterozygosities

BackgroundThe traditional exact method for inferring relationships between individuals from genetic data is not easily applicable in all situations that may be encountered in several fields of applied genetics. This study describes an approach that gives affordable results and is easily applicable; it is based on the probabilities that two individuals share 0, 1 or both alleles at a locus identical by state.ResultsWe show that these probabilities (zi) depend on locus heterozygosity (H), and are scarcely affected by variation of the distribution of allele frequencies. This allows us to obtain empirical curves relating zis to H for a series of common relationships, so that the likelihood ratio of a pair of relationships between any two individuals, given their genotypes at a locus, is a function of a single parameter, H. Application to large samples of mother-child and full-sib pairs shows that the statistical power of this method to infer the correct relationship is not much lower than the exact method. Analysis of a large database of STR data proves that locus heterozygosity does not vary significantly among Caucasian populations, apart from special cases, so that the likelihood ratio of the more common relationships between pairs of individuals may be obtained by looking at tabulated zi values.ConclusionsA simple method is provided, which may be used by any scientist with the help of a calculator or a spreadsheet to compute the likelihood ratios of common alternative relationships between pairs of individuals.

Forensic Entomology and the Estimation of the Minimum Time Since Death in Indoor Cases

Eight cases that occurred indoors in which the insects played an important role in the mPMI estimation are presented. The bodies of socially isolated people and old people living alone were discovered in central Italy between June and November. mPMI ranged from a few days to several weeks. Insects were collected during the body recovery and the postmortem. Climatic data were obtained from the closest meteorological stations and from measurements performed on the site. Sarcophagidae and Calliphoridae species were present in 75% of the cases with Lucilia sericata and Chrysomya albiceps collected in 50% of the cases. Chrysomya albiceps was always found in association with Lucilia species. Scuttle flies (Phoridae) were found in 37.5% of the cases, confirming the ability of these species in indoor body colonization. We show that if sealed environment may delay, the insect arrival dirty houses may create the environment where sarcosaprophagous insects are already present.

Development of a heptaplex PCR system to analyse X-chromosome STR loci from five Italian population samples. A collaborative study

Abstract A heptaplex PCR has been developed to amplify DXS6789, HUMARA, DXS10011, DXS7423, HPRTB, DXS6807 and DXS101 on Italian samples from Bologna, Modena, Padova, Ancona and Pisa. Statistical analyses were performed for all the loci.

Genotype probabilities of pairs of individuals for X-chromosome markers

BACKGROUND: The usual set of autosomal markers (A‐STRs) available in commercial kits is often insufficient to discriminate between close relationships when only two subjects are available for analysis. X‐chromosome markers (X‐STRs) provide higher statistical power in special cases.

The number of STR markers necessary to resolve relationships in deficiency paternity cases

Abstract The inference about the biological relationship between pairs of individuals using genetic markers plays a central role in many areas of human genetics. We investigated the number of markers (M) that are necessary to assign a given proportion of pairs (50%, 60%, 70%, 80%, 90%, 95%, and 99%) to their correct relationship at three predefined probability levels (99%, 99.9%, and 99.99%) against several alternative hypotheses. The following relationships were considered: (1) full sibs (FS), (2) second degree (2D, including half-sibs, grandparent–grandchild and avuncular pairs), (3) first cousins (FC), (4) unrelated individuals (UR).

Localization of DNA on a dishcloth used as a strangulation tool allowed perpetrator identification within a family

A case report of a domestic murder is presented. The victim was strangled with a kitchen cloth; the suspect, victims ex-husband, who still frequented the house, admitted of having used that cloth, though to dry his hands only. The pattern of DNA amplified from the cloth, belonging to both victim and suspect, allowed suspects version to be rejected. D 2003 Published by Elsevier B.V.

A multicentric study of SE33 allele frequencies in the Italian population

Allele and genotype frequencies for STR SE33 were obtained for a sample of 419 Italians in view of application in personal identification and paternity. D 2003 Elsevier Science B.V. All rights reserved.

Four unusual cases of disputed paternity evaluated by a likelihood ratio test based on the number of alleles shared identical by state (IBS)

Abstract We evaluated four unusual cases of disputed paternity in which only two subjects were available for analysis, with two different approaches. The first was the conventional method based on the posterior probabilities of observing the involved genotypes, given the alternative hypothesized relationships; the second was a new method based on the probability of sharing 0, 1 or 2 alleles identical by state (the IBS method). The new method is both conceptually and computationally easier, and has a comparable statistical power when markers with high heterozygosity are used.

Y-Chromosome variation and inter-haplotype mutational distances in 111 unrelated individuals from Tuscany, Italy

Abstract The phylogenetic median-joining network algorithm applied to 111 Y-chromosomes from Tuscany typed at 10 STR loci showed the existence of at least two well-separated clusters of haplotypes. We suggest that they correspond to different haplogroups.