Sex Difference and Inheritance Pattern of the Relative Difference of the 2nd and 4thDigits of Port Harcourt, Nigeria

The physical appearance of the difference in the index and ring finger has been associated with hormonal levels and sex. This study, therefore, evaluates the sex difference and heritability of the relative difference in the 2nd and 4th digits among families living in Port Harcourt. This research was designed as an observational, cross-sectional study involving 336 subjects comprising of 101parents and 135 offspring, obtained from 101 families within Port Harcourt, Rivers State. The second (2D; index finger) and fourth (4D; ring finger) digits were observed for relative difference in length; 2D<4D was noted as “SIF (shorter index finger)”, and 2D>4D noted as “LIF (longer index finger)”. The difference was determined by direct measurement using the digital vernier calliper (with an accuracy of 0.01mm), with a mathematical calculation (length of 2D minus 4D). The patterns were tabulated as family data and the parental combinations were highlighted to reflect offspring inheritance. XLSTAT (version 2015.4.01) Chi-square analysis (test) was used for association between sex and the difference in 2D & 4D at 0.05 significance level. While Mendelian Chi-square distribution modeltested the conformance to dominant-recessive inheritance. Parental and offspring allele frequency distribution were compared using Hardy Weinberg (H-W) equation. The analysis showed that 92.3% of the population had shorter index finger (SIF) compared to the 7.7% of the population with longer index finger LIF. There was no sex associated difference in the distribution (?2 [df=2]=1.659, P=0.436).The results from the parental and offspring pattern suggest that 2D:4D ratio is inherited.The Mendelian test of association suggest that the assumption of index finger inheritance in a dominant-recessive fashion. This was further strengthened by the result from the H-W calculations, which showed conformity of the offspring allele distribution (5:4:1) to that of the parents (5:4:1). The distribution of the difference in 2nd to 4th digit favoured the shorter index finger; without sexual preference. The conformity of the trait to the Mendelian simple dominant dominant-recessive inheritance was strengthened by the H-Wcalculation outcome which suggested a uniform pattern for the offspring and parent.

Key Words: 2D:4D, sexual variation, Mendelian inheritance, dominant, recessive, Nigerians.