That's based on mitochondrial DNA, which is passed from generation to generation unaltered through the maternal line. Every DNA test that has been done on Dominicans shows a majority have African mtDNA.
But, the majority also has European Y-chromosomes, which are inherited from the father line. And Taino DNA is also present in most Dominicans, despite most not having Taino Y-chromosomes or Taino mtDNA. On average, the Taino component ranges from 5% to 13%. Roughly 15% of Dominicans have Taino mtDNA, which means that their maternal line goes back to a Taino woman roughly 500 years ago, which is before the massive modern migrations of Europeans and Africans started.
On average, autosomal DNA tests have shown that the genome of the typical Dominican tends to be between 40% and 60% European, very rarely does the African component surpases 50%, and the Taino component hardly never is greater than 13%. This is on an individual basis, which varies even within blood-related brothers, because the typical Dominican is the product of mixtures, with remixing in every generation. For most of Dominican history, most Dominicans have been mating with people that are triracial, which simply causes a shuffle of each DNA origin, but all three components are present in most people. A minority of Dominicans have more than 60% of their genome originating in Europe. Asian and Oceanic origins are negligible as well.
The major problems regarding Dominicans, is that most foreigners make assumptions based on what happened in other places, without truly looking into how the Dominican society actually formed.
By the late 1600s, most of the population was already of mixed race and lived free, mostly as subsistence farmers. There is even an account by S?nchez Valverde, who was complaining that the severe lack of slaves in the late 1600s, caused the cacao harvest to go unpicked, at time when most of the population had at least some African ancestry.
By the time slavery was officially abolished in the mid-1800s, the liberation affected a minority of the population and most of the population had been living as free men for centuries. This is also why among the Trinitarios, Francisco del Rosario S?nchez, a typical Dominican mulatto, was able to form part of the independence movement, along with many other mulattoes and blacks. Had they been slaves, it would had been impossible.
By the time slavery ended in many other parts of the Americas, most Dominicans had been living as free men for centuries and this greatly impacted social relations and race relations in the country. It also was the main reason for why most Dominicans have never suffered from a strong resentment and hate towards whites, which is what bothers many African descended people from other parts of the Americas when they visit the country. They completely dismiss the social formation of the country and simply assume that it was similar to how it occurred elsewhere, when it didn't.
There are even historical accounts in which even the Haitian military were struck as to why the Dominicans went to the aid of their white neighbors, when the Haitian army began to attack them. The Haitian military and high ranking officials couldn't understand why most Dominicans didn't felt the resentment and the hate towards the whites, as they themselves felt. The answer is in the social formation of the country. While Haiti got its independence due to a slave revolt, with over half of its population having been born in Africa at the time they separated from France and almost the entire population subjugated to slavery; the majority of the Dominican population had been living free for centuries. This was even a cause for concern to the French plantation owners, because some of their slaves would escape and enter the Spanish part of the island, and their property (ie. the slaves) were never returned by the Spanish authorities. They were allowed to become subsistence farmers as free men and women.
Basically, the memory of the first slave sugar economy that started in the 1500s and had extinguished itself by the end of that century, the lack of new massive slave imports after that period, the extreme poverty that affected Dominican society, in which even the wealthiest households were quite modest; and the very few Africans that were still slaves and worked in cattle ranches; caused the extensive racial mixing that has characterized Dominican society since the late 1600s and reduced the resentments and the hatred. This was a memory that was still alive and well among the Haitians, considering that most of the Haitian troops had been slaves of the French a couple of decades before they militarily invaded the DR. They still had the anger that time had extinguished on the Spanish side of the island. And this resentment is what characterizes many African descended people in the Americas, especially those from the former British Empire (USA, Jamaica, and the British islands in the Lesser Antilles.)
Click on the following links to see the documents:
Quote in which Juan Pablo Duarte expresses his admiration for Haiti.
The law put in effect by General Pedro Santana and the rest of the Dominican government in July 1844, 5 months after achieving independence from the Haitian military domination.
The Slave Trade (1619-1808): Notice the small amount that were taken to the DR and the bulk were imported before the mid-1600s. Notice Haiti, Cuba, Jamaica, the USA, the Lesser Antilles. Also, keep in mind that in places like Cuba, large numbers of African slaves were imported until well into the 1800s, which explains why African influences have been better preserved there than in the Dominican Republic, despite a constant European influence.