The set of information responsible for defining skin pigmentation is written in the genes present inside our cells. So far, no news, right?
Several studies have shown that the genes responsible for various pigmentation phenotypes are related to transcription factors, the process of melanogenesis, the transport of enzymes during melanin synthesis, structural and membrane proteins, expression of different melanin precursors, and various receptors and their ligands in the membranes.
Moreover, this genetic information is available in databases along with the entire human genome for researchers to use in their molecular studies. With the latest technologies, some studies have used small molecular markers such as SNPs (single nucleotide polymorphisms, where the change of a single nitrogenous base can cause changes in protein transcription) to estimate the characteristics found in the most diverse human phenotypes.
All this available molecular information has been used to reconstruct the evolutionary history of patterns related to skin pigmentation in hominids. Thus, these genes have also been used in areas of forensic medicine that attempt to reconstruct the phenotype from DNA samples.
Based on this knowledge, Cerqueira and researchers from the Federal University of Rio Grande do Sul conducted a study where they sought to verify the reliability of predicting different phenotypes of hair, skin, and eye pigmentation using databases and genetic markers. A total of 124 SNPs associated with pigmentation were selected from the literature. The genotype of 11 individuals who had their genome completely sequenced, along with available photographs, were selected from two databases, USCS and PSU USCS. In addition to these genotypes, another 19, whose phenotypic information was not available, were selected for the test, including 5 from extinct hominids and 14 from anonymous individuals belonging to different ethnicities.
The authors considered the additive effect of alleles in homozygosity to predict characteristics related to multifactorial inheritance in the chosen genotypes. To test the efficiency of the chosen methodology, the researchers checked the consistency of the information by comparing the predicted phenotypes with the actual ones of those 11 individuals who already had their phenotype known.
Subsequently, they attempted to predict the characteristics of five other Homo species that already had their genome in a database, as well as 14 DNA samples from other anonymous humans. The phenotypes of these were assigned considering the average phenotype of the population to which they belonged and comparing them to the phenotype predicted by the molecular markers.
For the study, 18 phenotypes were chosen whose genetic inheritance was associated with genes in homozygosity. Among them were genes related to variations in skin color, presence of freckles, eye color, and hair color. The results showed an average concordance of 60% between the predicted and observed values.
The percentage of concordance between the predicted and observed value (known samples) and between the predicted and probable value (anonymous samples) of each of the observed characteristics varied slightly. But on average, the results showed a reasonable predictive value of 60%.
Since this was a pioneering study, these results were encouraging, as they suggest that genetic markers can be used to predict human phenotype based on genes related to skin, eye, and hair color. Of course, further studies need to be conducted since the role of certain genes in pigmentation still needs to be elucidated.
Certainly, some mothers who are eagerly awaiting the arrival of their babies must be thinking at this moment: why not make a prediction if my little one will be a freckled redhead with green eyes or a blonde with green eyes? Who knows, in a not-so-distant future...
In a few words, are we close to being able to determine the shapes and colors responsible for different phenotypes from a small DNA sample? Is biology close to reconstructing the phenotype of our ancestors in terms of just a few nitrogenous bases? And is forensic medicine close to having a “composite sketch” that does not depend on doubts or memory failures?
Carolina Lavini Ramos is a biologist graduated from the Institute of Biosciences at USP and holds a master's degree in Medical Sciences, with an emphasis on Immunology, from the Faculty of Medicine at USP. She currently teaches science for elementary education, guides students in the development of pre-scientific initiation projects, and is a member of the scientific review committee of the journal InCiência. She has a special interest in educational and outreach activities that bring scientists closer to society.
Contact: ca_Lavini@hotmail.com
Bibliographic Reference:
CAIO C. S. CERQUEIRA, VANESSA R. PAIXÃO-CÔRTES, FRANCIS M. B. ZAMBRA, FRANCISCO M. SALZANO, TÁBITA HUNEMEIER, AND MARIA-CÁTIRA BORTOLINI. Predicting Homo Pigmentation Phenotype Through Genomic Data: From Neanderthal to James Watson. AMERICAN JOURNAL OF HUMAN BIOLOGY 24:705–709 (2012).
