There's a new discussion on the Discussion Board about who is responsible for Alex's abilities. They point out that, if Alex is in such a rush to save his sperm, shouldn't everyone also be trying to save Frank's (Alex's father) sperm as well.
I'm not going to repeat the whole thing here, but I'll post the most recent entry, as it seems to provide the most informative answer on the subject.
Note that the writer talks about the "S" gene. This is because, during previous discussions about how the topic, we'd worked out between us that Alex's and the girls abilities don't seem to be from the same genetic anomaly as Alex's. As a result we described the girls as possessing the "S" (Seer) gene trait. It appears to be tied to the X chromosome, which would mean that someone with it trait on both their X chromosomes would likely become a Seer, while someone with it on only a single X chromosome would become a watcher.
Here's his response to the debate:
I noticed that discussion of genetics has led to the
pointing of the finger of genetic "fault" to Frank. Obviously, Frank
has not expressed Alex's gene (a mutant "S" gene) or even the "S" gene
itself. Neither has Linda. So, who's at fault? Since none of Alex's
siblings have expressed the "S" gene, the finger points at Frank for
being a mutant carrier. There are different possibilities, though.
Every time there is a cross over of genes from one chromosome to another,
there is an estimated 20% chance of an error. Humans have 50 such
events per gamete, so the chance of an error is very high
(99.9986%@20% per incident), which is why such a high percentage of
human spermatozoa and eggs are non-viable. This is also why there's
always a chance of a genetic error resulting in a spontaneous
(natural) abortion, stillbirth, or birth defect.
Some errors however, are undetectable. This is because ~20%
of our DNA is not transcribed. However, the purpose of some sequences
is to "promote" genes, indicating that this or that sequence is to be
transcribed. What if a promoter sequence was accidentally erased or
damaged? Then you have an permanently silenced gene. This is why the
"S" gene was endangered. Even if a lineage had the genes for a Seer or
Watcher, there could always be the chance that an error would result
in silencing of the gene. For example, Linda could have had a great-
grandmother that was a Seer. This means that 100% of the great-
grandmother's children should have been carriers of the gene. However,
if she married a non-"S" carrier (most-probable outcome), then all of
her daughters would only be Watchers (heterozygous for the "S" gene)
and since they are probably not going to marry an "S" carrier, there's
only a 50% chance of a female granddaughter being a non-activated
Seer. (However, all of her sons would still be "S" gene carriers.) If
an error occurred during meiosis and the promoter sequence for the "S"
gene was damaged, then the abilities would disappear, even if the "S"
gene was still being transferred. So a Seer lineage could easily
appear to die out if the great-grandmother only had one daughter.
Errors can also result in the activation of genes. A
silenced promoter sequence can be restored by pure chance during
crossing over. Or a new promoter sequence could be created. The result
could be good or bad, depending on the gene sequence being
transcribed. This is what probably happened to Alex. New sequences
were accidentally created and a new gene and its promoter came into
existence. If this is sex-linked, Frank is probably responsible for
part of this as this would have occurred when the sperm that was
responsible for Alex came about. However, how do you explain the
receptivity of the "S" gene carriers? Perhaps Alex also happens to
have one of those accidentally silenced "S" genes on his X chromosome.
Basically, his unique gene on his Y chromosome is expressing itself
along with a normally silent "S" gene on his X chromosome.
So, this is why taking a sample of Frank's cells or sperm
wouldn't help anything. Frank doesn't have Alex's gene-they were
unique to the sperm that produced Alex. Taking a sample of Linda's
cells might be useful if it turns out that she's a carrier of a
silenced "S" gene, but she wouldn't have Alex's genes either--that
would have been on the Y chromosome carried by the sperm that
fertilized Linda's egg.