Whitson graduated from Mount Ayr Community High School in 1978 and received a bachelor of science degree in biology and chemistry from Iowa Wesleyan College in 1981. She then went on to earn her doctorate degree in biochemistry from Rice University in 1986 , and following completion of her graduate work, continued at Rice as a Robert A Welch Post-doctoral Fellow until October 1986. She is married to Clarence F. Sams. Following her fellowship at Rice, she began working at Johnson Space Center in Houston, Texas, as a National Research Council Resident Research Associate. From April 1988 until September 1989, Whitson served as the Supervisor for the Biochemistry Research Group at KRUG International, a medical sciences contractor at NASA-JSC. From 1991 through 1997, Whitson was invited to be an adjunct assistant professor in the Department of Internal Medicine and the Department of Human Biological Chemistry and Genetics at the University of Texas Medical Branch in Galveston, Texas. In 1997, Whitson began a position as adjunct assistant professor at Rice University in the Maybee Laboratory for Biochemical and Genetic Engineering. From 1992 to 1995, she served as project scientist for the Shuttle-Mir Program and, until her selection as an astronaut candidate in 1996, as deputy division chief for the Medical Sciences division at the Johnson Space Center. From 1989 to 1993, Whitson worked as a research biochemist in the Biomedical Operations and Research Branch at NASA-JSC. From 1991 to 1993, she served as technical monitor of the Biochemistry Research Laboratories in the Biomedical Operations and Research Branch. From 1991 through 1992, she was the payload element developer for Bone Cell Research Experiment (E10) aboard SL-J (STS-47), and was a member of the US-USSR Joint Working Group in Space Medicine and Biology. In 1992, she was named the project scientist of the Shuttle-Mir Program (STS-60, STS-63, STS-71, Mir 18, Mir 19), and served in this capacity until the conclusion of the Phase 1A Program in 1995. From 1993 through 1996, Whitson held the additional responsibilities of the deputy division chief of the Medical Sciences Division at NASA-JSC. From 1995–1996, she served as co-chair of the U.S.-Russian Mission Science Working Group. In April 1996, Whitson was selected as an astronaut candidate and started training in August 1996. Upon completing the two years of training and evaluation, she was assigned technical duties in the Astronaut Office Operations Planning Branch, and served as the lead for the Crew Test Support Team in Russia from 1998 to 1999.