Genetic linkage is a specific term with a fixed meaning. As you have
mentioned, the distance from each other determines number of cross
overs. More info available at
Even with closely linked genes there is some cross over.
One gene = one peptide. They used to say one gene = one protein. But
the one amino acid sequence produced by a gene could be an enzyme,
co-enzyme etc. etc. This peptide usually is involved in one just
bio-chemical interaction, as part of the whole bio-chemical chain, in
The example I gave re the fish was to show that inbreeding depression
can be broken through out crosses. This was not a claim that breeding
two bad specimens would produce a good result. Just an example to
help show what inbreeding depression is all about.
Generally, on factors involving multiple genes, the mean of offspring
is somewhere between the results of the parents, usually very close to
the average. Then we have the variability. The greater the
variability, the more likely it is that you will get a seedling
exceeding the best parent. But they will all be on the distribution
curve, a "normal" distribution curve.
When comparing results of a cross, year one germination, to year two,
then need to focus on each colour pattern on its own. For example, the
number of white seedlings. First, you have the total for the cross.
And the percentage of whites out of total. Now you compare year one to
year two. Random distribution would be equal for each year. So now we
do a chi-square test. Compare results to randomly expected results.
For example, total whites in cross is 6. So random distribution would
be 3 in year one, and three in year two. Then we have what we got
compared to what is expected.
For a test of significance, for this number, a division of 0/6 or 1/5
would be significant. The 1/5 just barely. A distribution of 2/4
wouldn't be. The larger the numbers, the less dramatic the difference
needed to be mathematically significant.
This would need to be done with each colour type. With only four of a
type you need a 0/4 distribution to be significant, but this is barely
below the 5% significance level.
Just to give you an ides of how you figure this out. For more
information look up chi-square test.
From: Linda Mann <email@example.com>
To: iris-photos <firstname.lastname@example.org>
Sent: Fri, May 25, 2012 7:07 pm
Subject: [iris-photos] Re: HYB: 2nd year sprouts
I think we be talking past each other to some extent - terminology on
part. By "linked", I mean in the general sense - not that they are
close to each other in any physiological sense, only that they are on
the same chromosome. Maybe at opposite ends ;-) I'm not even
slightly familiar with frequencies/probabilities of crossing over &
relationships to distances along chromosome 'legs' (arms?), tho I
vaguely remember reading about studies of such. As I recall, the
farther away, much higher probability of crossing over, which is why I
guess the close ones are considered 'linked'.
> is not the same as factors linked by having
> genes closely aligned physically on same chromosome
This is what I thought you were implying. ;-)
> All my genetics and statistic forensics say these two samples are
> from same two parents.
Mary Lou, any chance pot/refrigerator baggie labels migrated from one
year to the next?
The one cross I saw the biggest color difference from first year to
second year germination was definitely the same pot (IMM X CSONG). But
there was some overlap, sort of, of colors. Most germinated the first
year - mostly creams, a few whites, one yellow, two rosepurple selfs,
one bluepurple amoena. Second year several whites (including one
t-bearded - so much for first year easy germ of t factor with no
anthycyanin), a few "pink" anthocyanin amoenas, one bluepurple amoena,
no creams, no selfs. Enough overlap of 'types' that I can believe that
color was random in relation to chilling requirements.
Another question - are you saying that crossing two "poor quality"
inbred lines always produces "good quality" offspring? Surely not.
Depends on what other 'junk' is dragged along in the two inbred lines.
If both inbred lines have (back to irises) summer crud susceptible
foliage, then I'd expect the outcross seedlings to have it too. Same
concept with outcrossing two inbred pink lines - if both have early
germination, why would it go away in the offspring? I can't understand
why that trait would suddenly acquire a "normal" distribution.