Superfecundationis the fertilization of two or moreovafrom the samecyclebyspermfrom separate acts ofsexual intercourse. The term superfecundation is derived fromfecund, meaning the ability to produce offspring.Heteropaternal superfecundationoccurs when two different males fatherfraternal twins.

In common usage, the term superfecundation is often used instead of heteropaternal superfecundation. The terms are practically equivalent because, though superfecundation by the same father is thought to be a common occurrence, it can only be proven to have occurred with multiple fathers.[1]Contents

[hide] 1Conception 2Heteropaternal superfecundation 3Use in mythology 4See also 5References 6External linksConception[edit]Superfecundation most commonly happens within hours or days of the first instance of fertilization with ova released during the same cycle. The time window when eggs are able to be fertilized is small. Sperm cells can live inside a female's body for four to five days. Once ovulation occurs, the egg remains viable for 1248 hours before it begins to disintegrate. Thus, the fertile period can span five to seven days.

Ovulationis usually suspended duringpregnancyto prevent further ova becoming fertilized and to help increase the chances of a full-term pregnancy. However, if an ovum is released after the female was already impregnated when previously ovulating, a chance of a second pregnancy occurs, albeit at a different stage of development. This is known assuperfetation.

Heteropaternal superfecundation[edit]Heteropaternal superfecundation is common in animals such ascatsanddogs. Stray dogs can produce litters in which every puppy has a different sire. Though rare in humans, cases have been documented. In one study on humans, the frequency was 2.4% amongdizygotic twinswhose parents had been involved inpaternity suits.[2]Use in mythology[edit]InGreek mythology,Heraclesand his twinIphiclesare examples of heteropaternal superfecundation, with Heracles fathered by the godZeusand Iphicles by a mortal man Amphitryon.

In another Greek myth,Ledaconceives four children (Helen of Troy,Clytemnestra, andCastor and Pollux) in the same night by two different men. Two are children of Zeus, who comes to Leda disguised as a swan, and two are the children of Leda's mortal husband,Tyndareus. Which men father which children varies widely among accounts, in some cases establishing that the Gemini twins Castor and Pollux are born of different fathers. The heteropaternal superfecundation involved in this myth is especially unusual, because instead of giving birth to the children, Leda lays eggs that hatch them.

See also[edit] Chimera (genetics) Mixed twinsReferences[edit]1. Jump up^James, William H. (1980)."Gestational age in twins".Archives of Disease in Childhood55(4): 281284.doi:10.1136/adc.55.4.281.PMC1626817.PMID7191240. Retrieved2011-03-17.2. Jump up^Wenk RE, Houtz T, Brooks M, Chiafari FA (1992). "How frequent is heteropaternal superfecundation?".Acta geneticae medicae et gemellologiae41(1): 437.PMID1488855.The frequency of HS among dizygotic twins whose parents were involved in paternity suits is 2.4%External links[edit] "Is it possible for fraternal twins to have different fathers?" atThe Straight Dope Lu et al. (July 1994)."Paternity Identification in Twins with Different Fathers".Journal of Forensic Science39(4): 11001102. Gawker (18 May 2009) Doctors Discover Dallas Twins Have Two Different Dads