Re: Genetic Question - Genetic Similarity of Same Seed Crosses

"If two growers grow the same seed and pollinate the
same cross do the seeds from the two pumpkins have
identical genetics?"

This is a good genetic question that provides insight
into why there is so much variability in the pumpkins
produced from the same seed.

The short answer is: perhaps, but it's not very likely
that they have identical genetics.  The odds of two
same-cross pumpkins having identical genetics in their
seeds are as bad as 1 chance in 16.

The long answer gets rather complicated. When two
pumpkins strains are crossed by a breeder, the
resulting seeds have one of four distinct genetic
makeups.  This is due to the fact that the mother and
the pollinator only contribute half of their genetic
makeup to each individual seed.  There are four
combinations of genetic material from the two parents
possible.   So, if there is four hundred seeds in the
pumpkin, there should be roughly 100 seeds of each
possible genetic combination.  

Another mechanism called cross-linking ensures that
there is some minor variation in each group of these
100 similar seeds. (cross-linking is the nasty habit
of chunks of dna to split from one allele and attach
to another in a somewhat random manner)

So if you plant the same seed as another grower, you
have only one chance in four of growing a plant with
the same(or very similar) genetics.

If you cross the same two plants as another grower,
the chances that you have the identical genetic mother
and pollinator seed is (one in four) times (one in
four) or one in 16.

Again the seed that is produced by either pumpkin will
have four distinctly different genetic makeups
comprised of the alleles of the two parent pumpkins.

It is more likely that the groups of seeds from the
two same-cross pumpkins will have absolutely no
genetic crossover, than they will be identical
genetically.

If either of the parent or grandparent pumpkins were
selfed or sibbed, the odds of the two groups of seeds
having identical genetic makeup improve dramatically.
So selfing and sibbing can help reduce variability in
the seed stock.

Keep this in mind before plugging down several hundred
bucks for a hot seed.  It may not have a single gene
you want and that hot sounding cross may be a real
loser.

vince
best 789 lbs. 2000
zone 9, the no clone zone



>-----Original Message-----
>From: Ned Sandercock <nedsand@pare.org>
>To: pumpkins@mallorn.com <pumpkins@mallorn.com>
>Date: 15 February 2001 16:33
>Subject: genetic question
>    
> Being a second year grower maybe you can help me
> out on a genetic question.  If two growers grow the
> same seed and pollinate with the same cross and
> their weights substantially vary due to some growing
> practice what makes the larger pumpkins seeds more
> desirable than the smaller one.  If Howard Dill and
> I both plant the Checkon 835 and cross it with the
> Rockwell 771.6.  I know Howard may get a Dill 990
> and I would have a Sandercock 202 but wouldn't the
> seeds from those pumpkins have an equal chance to
> pop a big one with their identical genetic
> background?
>      
>Ned
>1st year ):   189



__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail - only $35 
a year!  http://personal.mail.yahoo.com/

---------------------------------------------------------------------
Pumpkin-growing FAQ: http://www.mallorn.com/lists/pumpkins/search.cgi
To sign-off this list, send email to majordomo@mallorn.com with the
message text UNSUBSCRIBE PUMPKINS
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index