Researchers have found population differences in the behaviour of immune system genes - potentially affecting how people respond to infection.
The researchers looked at the activity of over 9,000 genes
The Chicago University team looked at over 9,000 genes in 180 people, half Caucasian and half from Nigeria.
They found differences between the two races in 5% of key genes.
The American Journal of Human Genetics study may help explain why some groups are more vulnerable to disease, and aid development of more tailored treatment.
The researchers used gene chip array technology, which uses a microscope to analyse a specialised slide capable of containing thousands of genes derived from blood cells.
Sixty nuclear families, each including a mother, a father and a child were studied. Thirty were from Utah in the US, while the rest were Yorubans from Ibadan, Nigeria.
The researchers looked at expression levels - how active a gene is.
They found significant differences, particularly in immune system genes involved in producing antibodies to combat bacterial infection.
This backs up previous work which has shown African Americans may be more susceptible than Caucasians to infection, such as the gum disease bug Porphyromonas gingivalis.
The US study also found activity levels varied significantly in genes involved in basic cellular processes which are thought to play a part in how the body responds to drugs, including the risk of side effects.
'Small and subtle'
Professor Eileen Dolan, who led the research, said: "Our primary interest is the genes that regulate how people respond to medicines, such as cancer chemotherapy.
"We want to understand why different populations experience different degrees of toxicity when taking certain drugs and learn how to predict who might be most at risk for drug side effects."
She added: "Population differences in gene expression have only recently begun to be investigated.
"We believe they play a significant role in susceptibility to disease and in regulating drug response.
"Our current research focuses on how these genetic and expression differences play a role in sensitivity to adverse effects associated with chemotherapy."
Dr Chris Tyler-Smith, a geneticist at the Wellcome Trust's Sanger Institute, said genetic differences between ethnic groups were "small and subtle".
"They usually just consist of slight differences in frequency of a few variants found in all populations. But they are important for our understanding of recent evolution and can have medical implications as well.
"They have been difficult to identify, and it is particularly interesting to see that characteristics like variation in susceptibility to infection are showing up."