In genetics, a non-paternity event is when someone who is presumed to be an individual's father is not in fact the biological father. This presumption may be on the part of the individual, the parents, or the physician. Non-paternity may result from sperm donation, undisclosed adoption, intercourse with multiple partners in close succession, non-consensual sex, as well as medical mistakes, for example, mixups during procedures such as in vitro fertilization and artificial insemination. Where there is uncertainty, the most reliable technique for establishing paternity is genetic testing; however, there is still a risk of error due to the potential for gene mutations or scoring errors.
Overall, the incidence of misattributed paternity ranges from about 2% to 12%, though it may be higher in certain populations. The discovery of previously unsuspected or undisclosed non-paternity may have both social and medical consequences. Non-paternity that is due to a previously undisclosed extra-marital relationship often has serious consequences for a marital relationship. Non-paternity is medically relevant when interpreting the results and utility of genetic screening for hereditary illnesses.
Definitions and uses
Bellis et al. (2005) stated that misattributed paternity "occurs when a child is believed to have been fathered by the husband (or partner) but is actually the progeny of another man." Non-paternity events are also sometimes referred to as misattributed paternity, paternal discrepancy or false paternity. Although it is sometimes referred to as paternity fraud, this suggests that the misattribution was deliberate rather than accidental. In a scientific review of non-paternity studies since the 1950s, Bellis et al. (2005) stated that knowingly covering up an accidental pregnancy that resulted from infidelity is often assumed to be the reason for non-paternity, but that there are many other reasons, "for example, where sex with the long term partner has not produced children a woman might seek conception elsewhere." They said other reasons might be undisclosed adoptions, accidental misattribution resulting from multiple relationships in close succession as well as medical mistakes, such as mixups during procedures such as in vitro fertilization and artificial insemination.
In genetic genealogy the term non-paternity is often used in a wider context to indicate a break in the link between the Y-chromosome and the surname. Such a breakage may occur because of formal or informal adoption, premarital or extramarital intercourse or rape, or when individuals use a different surname than their biological father, such as their mother's maiden name, a stepfather's name, the use of aliases or a legal name change.
Testing for non-paternity
The most reliable test for paternity is genetic testing, sometimes referred to as DNA testing. Requirements for consent and counselling vary by country. However, genetic testing is based on probabilities and is not always definitive. Jones et al. (2010) said, "Characteristics of the markers and the fact that they are analysed by fallible humans can result in inconsistencies that present problems for parentage analysis." False negatives may occur due to low quality samples, gene mutations, or genotyping errors (when a genotype is misread or inaccurately scored). There is a higher probability of accuracy when DNA from both parents can be tested. The accuracy increases even more when DNA from a sibling is available.
Rates of non-paternity
It is difficult to accurately estimate the incidence of misattributed paternity, and there have been large discrepancies in the research published on the topic. Often data on non-paternity rates are reported tangentially to the primary goal of research without sufficient detail, and very few studies involve randomized samples. As such, it is not possible to make valid generalizations based on a large portion of the available literature. Bellis et al. (2005) found that between 1950 and 2004, the rates of misattributed paternity published in scientific journals ranged from 0.8% to 30% with a median of 3.7%. According to a study published in the Lancet, "High rates have been quoted, but are often unsupported by any published evidence or based on unrepresentative population samples."
Turi King and Mark Jobling of the Department of Genetics at University of Leicester called the commonly cited 30% rate of non-paternity an "urban myth". According to King and Jobling, the figure is around 2%. They also stated that misattributed paternity is often impacted by cultural and socioeconomic factors and that it occurs more frequently among couples who aren't married. Sociologist Michael Gilding concluded that inflated figures have been circulated by the media, the paternity testing industry, fathers' rights activists and evolutionary psychologists. He traced many of these overestimates back to a 1972 conference where non-paternity rates as high as 30% were discussed. Gilding states that these data only show the incidence of non-paternity in cases where disputed parentage was the reason for paternity testing.  In situations where disputed parentage was the reason for the paternity testing, there were higher levels with an incidence of 17% to 33% (median of 26.9%). Most at risk of parental discrepancy were those born to younger parents, to unmarried couples and those of lower socio-economic status, or from certain ethnic and cultural groups.
Atypical multiple births
Rarely, genetic testing has revealed children from multiple births to have different fathers, which is known as "heteropaternal superfecundation". One study estimated that the incidence of bipaternal twins born to white women in the United States is around one pair in 400. Another study found the prevalence to be approximately one pair in 13,000 cases.
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