Based on the data for Rh, PF1 could not be the father of Twin
2 and PF2 could not be the father of Twin 1. Based on the data
for Hp (haptoglobin), PF2 could not be the father of Twin 1. The
HLA typing also indicates that PF1 could be the father of Twin 1
but not the father of Twin 2 and that PF2 could be the father of
Twin 2 but not the father of Twin 1. The probability that both
twins were fathered by a third (unnamed) man was 1/140,000 or
0.0007%.
Case Five
In a rare finding, a pair of twins have been show to have
different fathers. The case came to light when a woman in Spain
gave birth to twins and the husband, suspecting they were the
result of an affair, demanded DNA fingerprinting to see if he
was the father.
Tests showed that one of the fraternal (non-identical) twin
girls was indeed the husband's child, with a certainty of
99.9999998 %. But the other twin was clearly not his, according
to a report in the June issue of Fertility and Sterility. Out of
28 genetic loci tested (including blood type, enzymes and DNA)
the husband was excluded as the parent of the one twin in 9 of
the genes. Testing showed both infants were related to the
mother, so a hospital mix-up was not to blame.
The mother later admitted she had sex with another man within
a few days of having sex with her husband. Apparently her
ovaries released two eggs that month instead of the usual one,
and each was fertilized by a different man's sperm.
Only a few other such cases have been reported, but they may
be more common than expected. Increased use of fertility drugs
that stimulate the release of multiple eggs may explain an
apparent escalation in this phenomenon. But the
"trend" may be an artifact of increased and more
accurate paternity testing revealing a long-standing but little
known phenomenon.
Evolutionary biologists theorize that it's smart for females
to have occasional dalliances to produce a wider variety of
offspring that carry the mother's genes. Consistent with that
theory, researchers have found that married women are more
likely to have affairs during the time of month they are most
fertile. Even among unmarried couples, research indicates a high
rate of infidelity. In this case, females tended to rate their
extra-pair partner as more attractive while males tended to rate
their extra-pair partner as less attractive. One could conclude
that females are attempting to maximize the attractiveness of
their possible offspring while relying on a "steady"
in-pair partner to provide for the family. And that males are
just interested in increasing the number of progeny bearing
their DNA.
Case Six
Sylvia Bows, a high-powered corporate executive at San
Francisco's Silicon Impressions Inc., is a new mother of twins.
Congratulations, Sylvia, you're going to be a busy woman. But
maybe not as busy as you used to be.
According to a lawsuit filed in Superior Court last month,
Sylvia was very busy indeed "cutting a sexual swath"
through the high technology company, sleeping with every brainy
guy she could find. Eleven men, all SII employees, have actually
been named as sexual partners within a three month period in
1996. In fact, she's even been accused of breaking into the
company's health records to rule out men diagnosed with AIDS.
But, according to the complaint, Sylvia wasn't just being
promiscuous--she was trying to get pregnant. And pregnant she
became! Sylvia gave birth on March 17th to twins, but not
ordinary twins. These twins have different gestational ages.
What does that mean? Well, Sylvia apparently ovulated twice
in the same month. She got pregnant once and then, three weeks
later, got pregnant again. Because of Sylvia's sexual activity
at this time, the father of each twin might not be the same man.
Imagine, biological twins who have different fathers! A twin
half-brother!
I asked a medico of my acquaintance and he says that twins of
different gestational ages happen occasionally although they're
exceedingly rare. And he didn't know of any cases where the
twins were born to different fathers.
Where was Sylvia's husband during this time? According to court
papers, Tom Bows had undergone a vasectomy. And apparently
Sylvia and Tom's marriage was a bit shaky, presumably getting
more fragile after he discovered why Sylvia had been working
late.
And so the lawyers have gotten involved. Before the twins
were even born, Tom filed a lawsuit against Sylvia seeking sole
custody. But he couldn't be the father, you say? In California,
children conceived during a marriage are conclusively presumed
to be those of the husband, regardless of the actual genetics of
the matter.
And then Sylvia became the subject of another lawsuit. One of
the possible fathers--Richard K. Watson, also of SII--has also
filed a lawsuit seeking custody. In his complaint, he argues
that he is the actual father of both of the twins. Winters
claims that he was used as "an unwilling sperm donor to
further Sylvia's plan to become pregnant." He provides a
table of the names of many of those with whom Sylvia had
liaisons together with the dates of their sexual activity to
back up his claim of paternity.
In fact, there has been a parade of possible fathers. Sources
inside Silicon Impressions report the existence of an office
pool to wager on the identity of the real fathers. And,
according to hospital sources, there have been at least three
men, all claiming to be the father, coming to visit the infants.
Two of the potential fathers even broke into a scuffle in the
infant intensive care unit of the hospital.
So what's a girl to do? According to a response to Watson's
suit filed by the husband's lawyer, Sylvia and Tom are
attempting a reconciliation. They ask the court to dismiss
Winters custody suit as a "violation of the sanctity of
their marriage."
So the legal tangle will take a while to sort itself out. In
the meantime, Sylvia is home with the twins and her husband Tom.
One only can wonder what their pillow talk is like.
Answer questions 1-2
1) Write a summary how we can test for paternity.
2) How is it possible for fraternal twins to have different
fathers?
