The first results of the most comprehensive genetic sequencing project ever carried out in Brazil show that genes inherited exclusively by maternal means are generally black and native, and that genes transmitted by fathers are almost all from European colonizers.
The DNA do Brazil project aims to analyze the genome of 40,000 Brazilians. This is the largest research of its kind ever carried out in the country, and it will result in the most comprehensive genetic database available on our population. The initiative was announced nine months ago, in December 2019, and is already delivering its first results.
The researchers have already completed the genome sequencing of 1,247 Brazilians. Volunteers come from all parts of the country, which includes from riverside communities in Amazonia to residents of the city of São Paulo. One of the objectives of the research is medical: genetic data allow the identification of groups that are more susceptible to certain diseases, which makes it possible to direct SUS (Unique Health System) resources and efforts with intelligence.
Genetic mapping also provides data on volunteers' ancestry. Only in these 1,247 preliminary genomes has it already been possible to observe genetic variants stemming from 54 populations around the world. The results show that yes, Brazil is extremely miscegenated - but that this miscegenation did not occur in a balanced way.
Branding of a native woman Painting by Miguel Covarrubias
Half of our genes are inherited from our mother, while the other half is from our father. In general, it is not possible to identify which genes came from each of them. But there are exceptions.
The Y chromosome is one of them. Women have sex chromosomes XX, and men, XY. This means that the mother will always transfer the X chromosome to the fetus. And then the father's sperm is responsible for "deciding" the sex of the baby, sending the X or Y chromosome.
This means that every Y chromosome found in the population always comes from the father, allowing to trace the lineage of men in the country. The same goes for the mitochondrial DNA in relation to women. It is always the mother who passes the mitochondria to the son - mitochondria are energy producers of the cells that have their own genetic material -, so all DNA of the mitochondria of a population was necessarily inherited from women.
Now, to the results: 75% of the Y chromosomes in the population are inherited from European men. 14.5% are African, and only 0.5% are indigenous. The other 10% are half from East and South Asia, and half from other places in Asia.
With mitochondrial DNA it was the opposite: 36% of these genes are inherited from African women, and 34% from indigenous women. Only 14% come from European women, and 16% from Asian women.
Adding up the female percentages, we have that 70% of the mothers who gave origin to the Brazilian population were African and indigenous - but 75% of the fathers were European. The reason goes back to the years of Portuguese colonization in Brazil. The rape of black and indigenous enslaved women was the pattern.
Violent exploitation and mass extermination also caused indigenous men to leave almost no descendants - they represent only 0.5% of the genome in the population, while native women total 34%. “What happened was to kill or subdue the men and rape the women,” says Tábita Hünemeier of the Institute for Biosciences (IB) at São Paulo University, who studies population genetics and is one of the coordinators of the project.
Numbers like these are not new to genetics. “This is the Latin American standard,” says Hünemeier. The same happens in the population of countries like Colombia and Cuba, which also had Iberian colonization. Other genetic studies carried out in Brazil, which analyze only the Y chromosome and mitochondrial DNA, have been showing this same tendency since the years 2000.
Besides shedding light on historical atrocities, the genome of the first volunteers of the project also revealed four million new genetic variants, which are not registered in other international genome banks. Another recent genomic mapping, done only with elderly Brazilians, showed two million new variants.
“Three young white men and a black woman”, aka “The Rape of the Negress”, painting by the Dutchman Christiaen van Couwenbergh, 1632. Museum of Fine Arts of Strasbourg