Re: Seeds
- To: i*@onelist.com
- Subject: Re: [iris-talk] Seeds
- From: J* C*
- Date: Tue, 28 Mar 2000 18:46:00 PST
From: "Jan Clark" <janclarx@hotmail.com>
>Hi Jim and all,
> Jim, this is Dean from your neck of the woods. Please, someone answer a
>question for me, I really feel stupid for not knowing this. I would think
>all seeds from one seed pod would be the same. However, I have a hunch
>that
>may not be true. Can someone please put me out of my misery, are all seeds
>from one pod all alike? As you can tell, I'm in the early stages of Iris
>Illness.
If you grow a batch of iris seeds from one pod, you can expect a range of
different plants. Different in flower colour, substance and form, growth
habit, leaf shape and colour, rate of increase, resistance to disease, etc.
That's why it is such fun to hybridise the darn things.
Each seed forms from a 2 gametes (or sex cells) each of which contains 1/2
of the genetic material of the parent plant from which it came from. (The
pollen grain contains a large number of male gametes, not just one.)
A modern TB generally has 48 chromosomes. This is 4 sets of 12 chromosomes.
Generally 2 sets of 12 will go to the gamete cell.
If you consider chromosome 1, of which there are 4, these may all be quite
different, and your gamete has a 1 in 4 chance of receiving a particular
chromosome, and a 1/6 chance of receiving any 2 particular
strands of chromosome 1. The number of combinations possible is roughly 6 to
the power of 24. I'm not absolutely sure of the maths here, but that gives
you an idea how much variation is possible, especially with a wide cross.
The more closely bred the parents, the more chromosomes they will have in
common, so the less the variation.
Some hybridisers try and breed closely (line breeding) to increase the
likelyhood of breeding a particular trait into their seedlings.
Even more variation is possible, because chromosomes are capable of swapping
sections of the chain with another like chromosome, during cell division.
Certain traits will show up more commonly than others because of the
dominance of some genes on the chromosome strand, over the equivalent gene
on the other strands.
"The World of Iris" has details of which traits are dominant or recessive in
Tall Bearded Irises, and we have had many discussions in the past, which can
be found in the archives.
Happy reading!
Cheers, Jan Clark, Australia
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