My Research Projects

Postdoctoral Training Project: Genetic Research of Health Disparities

For my postdoctoral research project, I am conducting genetic epidemiological research on genetic and environmental determinants of serum vitamin D concentration and its association with prostate cancer risk in African Americans.  Cancer incidence and mortality rate is disproportionate among the racial/ethnic groups in the U.S. and higher in African Americans (AAs).  Multiple factors, such as socio-cultural (education, income, unequal access to health care, and lifestyle/behavior) as well as biological/genetic factors, contribute racial/ethnic health disparities. (Here, I explain why I am interested in prostate cancer disparities).

Several researchers have proposed that the differences in serum vitamin D, 25(OH)D, concentration among racial/ethnic groups is one of the sources of health disparities.  Vitamin D has protective effects against many chronic diseases, such as cardiovascular disease, diabetes, high blood pressure, autoimmune diseases, well as several types of cancer.  Vitamin D deficiency is more common among AAs than the European Americans (EAs), probably due to skin color, lifestyle, and genetic differences.  Vitamin D deficiency is very common even AAs from southern states.

At Community Health Screening Event, Summer 2012

Members of Dr. Kittles’ Lab At Community Health Screening Event (Summer 2012) .  I am standing next to Dr. Kittles.

Dissertation Research: Effects of female gene flow vs. effective population size on mitochondrial DNA (mtDNA) genetic variation among the Bantus in Africa and native populations of the New World

Many studies used sex-specific genetic markers (mtDNA and Y chromosome) on global and continent-wide population samples and found higher mtDNA diversity compared to Y chromosome diversity.  Kinship structure, or mating pattern, is considered to be an important factor influencing genetic variation and regional studies have linked patricentric structure with large mtDNA diversity and matricentric structure with low mtDNA diversity.  Researchers have hypothesized that either high female gene flow through marriage exchange and postmarital residence patterns or large female and reduced male effective population sizes caused by large variance in male reproductive success (or a combination these factors) could explain the observed asymmetric genetic patterns in patricentric societies.

NIsland Migration Model

N-island Migration Model

In my dissertation, focusing on mtDNA variation among the Bantus in Africa and native people in the New World, I examined A) whether the asymmetric genetic patterns observed between sex-specific markers are mostly the result of high rates of female gene flow/admixture or of reduced male effective population size due to high variance in male reproductive success and B) the extent to which kinship structure (here defined as patricentric or matricentric) affects the importance of each factor.  Kinship structure predicts the pattern of female gene flow, within population genetic diversity, and pattern of population structure.  Based on how kinship structure affects mtDNA variation, I examined how Bantu populations interacted with non-Bantu East African populations as they expand into East Africa.  Bantu kinship structure can explain how East African Bantus became genetically heterogeneous.  The native populations of the New World experienced three major demographic events (founder effect during the initial settlement, population expansion.  Kinship structure of population helps understand how demographic events affected mtDNA variation as well as how new world populations are genetically related to each other.

Genetic Variation of the Taita and Mijikenda in Kenya

We are investigating genetic variation of two Bantu ethnic groups living in Bantu expansion periphery.  Samples collected from different Bantu populations are often analyzed in human population and medical genetics studies, but genetic variation exist among them is not yet well understood.  Contrary to dominant view, mtDNA data reveals that the East African Bantus are heterogeneous groups, as a result of interaction with different non-Bantu East African populations.  The Taita tribes are genetically diverse and more similar to non-Bantu East Africans than to Central African Bantus and the Mijikenda tribes are genetically differentiated from each other.  We recently started analyzing Y chromosome variation among them to compare to mtDNA data.  (Here is the link to my Bantu expansion paper)

Taita Mijikenda Map

Taita Mijikenda Map

Ancient DNA Projects

We tried to understand the genetic relationship of ancient Andean populations.  We analyzed mtDNA variation of skeletal remains from three coastal sites (Nazca, Kilometer 4, and Chiribaya Alta) and compared to other ancient and modern highland populations.  Haplogroup B frequencies are higher among the highland populations than the coastal populations and peak around southern Peru, Bolivia, and northern Chile.  Different scenarios of migration events were examined.  We also conducted preliminary research of Colonial era Swahili and the Iron Age Albanian skeletal remains.

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