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Penelope "Penny" Jeggo is a noted British biologist, best known for her work in understanding damage to DNA.

Early life and education
Penny Jeggo was born in Cambridge, England. She earned a bachelor's degree in microbiology at Queen Elizabeth College, University of London in 1970. She went on to earn a PhD in genetics at the National Institute for Medical Research (NIMR), London, in the lab of Robin Holliday.

She later held postdoctoral positions with John Cairns, whom she cites as one of her biggest mentors, at the Imperial Cancer Research Fund Mill Hill Laboratory, and with Miroslav Radman at the Université libre de Bruxelles, Belgium.

Career and legacy
Jeggo's primary legacy is her work on DNA damage responses and DNA repair of double strand breaks. Much of her early worked involved Chinese hamster ovary cells, a commonly studied cell line also known as CHO. Using standard techniques of microbial genetics, she tested more than 9,000 colonies before isolating six X-ray-sensitive mutants. This was the first step in understanding the mechanisms involved in the repair of X-irridiation-induced DNA damage.

Jeggo is particularly well known for identifying two components of an enzyme called DNA-dependent protein kinase (DNA-PK) as being important in DNA non-homologous end joining (NHEJ), a pathway by which mammalian cells repair themselves. This discovery was a major breakthrough in understanding the double strand break repair pathway in mammals. In addition, Jeggo showed that NHEJ is important for the development of the immune response. She also studied LIG4-mutant mice and how exposure to oxygen increases the number of double-stranded breaks due to the failure to repair DNA breaks.

In 2001, Jeggo became a founding member of the Genome Damage and Stability Center, a research center established at the University of Sussex.