Y-chromosome diversity in Catalan surname samples: insights into surname origin and frequency

Abstract

The biological behavior of the Y chromosome, which is paternally inherited, implies that males sharing the same surname may also share a similar Y chromosome. However, socio-cultural factors, such as polyphyletism, non-paternity, adoption, or matrilineal surname transmission, may prevent the joint transmission of the surname and the Y chromosome. By genotyping 17 Y-STRs and 68 SNPs in ~2500 male samples that each carried one of the 50 selected Catalan surnames, we could determine sets of descendants of a common ancestor, the population of origin of the common ancestor, and the date when such a common ancestor lived. Haplotype diversity was positively correlated with surname frequency, that is, rarer surnames showed the strongest signals of coancestry. Introgression rates of Y chromosomes into a surname by non-paternity, adoption, and transmission of the maternal surname were estimated at 1.5-2.6% per generation, with some local variation. Average ages for the founders of the surnames were estimated at ~500 years, suggesting a delay between the origin of surnames (twelfth and thirteenth centuries) and the systematization of their paternal transmission. We have found that, in general, a foreign etymology for a surname does not often result in a non-indigenous origin of surname founders; however, bearers of some surnames with an Arabic etymology show an excess of North African haplotypes. Finally, we estimate that surname prediction from a Y-chromosome haplotype, which may have interesting forensic applications, has a ~60% sensitivity but a 17% false discovery rate.

Figure 1

Map of NE Spain.

Figure 2

Scatter plots showing (a) haplotype diversity and (b) the proportion of the sample in a MDC as a function of the surname frequency.

Figure 3

Multidimensional scaling (MDS) analysis based on pairwise R_ST calculated from Y-STR haplotype frequencies in 50 surnames (abbreviations as in Table 1) and in the Catalan and Italian (black stars) general populations.

Figure 4

Haplogroup and Y-STR haplotype diversity within six selected surname samples represented by median-joining networks presented in decreasing surname frequency. Each circle represents a haplotype with its size proportional to frequency. Each circle has been colored according to haplogroups (see key), and the lines between them indicate the Y-STR mutational steps. MDCs are indicated with dotted ellipses. A full colour version of this figure is available at the European Journal of Human Genetics online.