This is probably of no interest to anyone but me.
The number of heterozygotes (Ii+) that have black spots is line dependent. We did two broiler lines with dominant white and crossed them to Black Australorps. All chicks should have been Ii+ heterozygotes, but only 60% of the chicks from one line had black spots and only 15% of the chicks from the other line had black spots. This is an average from multiple sires from each line. Some sires had more some less. One hatch we had almost no chicks with black spots from the low spot line, but the second hatch we had more, using the same males and females. Spotting may be influenced by the incubator environment.
Thank you for discussing your experience with the
It's fun to see the statistics work out like they're
supposed to. (Usually things don't go quite so
well!) I have no real point in this post, it is just fun
to see the genetics work out.
We have the F2 generation of a breeding project in
the brooder now. The F1s are (should be,
anyway!) all heterozygous for dominant white. So,
the F2 generation will (should be) 25%
homozygous for dominant white, 50%
heterozygous for dominant and 25% completely
lacking dominant white. The P generation are
Araucana sires and White Leghorn dams so all the
generations should be homozygous for extended
black.
The idea this morning was to try to judge the
genetics by just looking at the chicks. Completely
yellow chicks with no black spots anywhere were
sorted to the homozygous category. Yellow chicks
with black spots go to the heterozygous
classification and non-yellow chicks are judged to
be lacking any dominant white.
With this simple-minded system for judging, we
have exactly 25% of the F2 chicks that have no
dominant white at all. This 25% are not all black
but most are. The ones that aren't black are
explainable in terms of black modifyers expressing
in the chick down. The proportion of heterozygotes
(for dominant white) is almost 50% judging by the
black spots visible in the yellow down. The
remaining, completely yellow, chicks should be the
25% that are homozygous for dominant white. I
am a little bit bothered by the presumption that all
I/i+ heterozygotes should have black spots ... I don't
know that this is true.
By Rokimoto on Wednesday, December 5, 2001 - 02:45 pm:
Something funny happened with some of the chicks that we saved from the line with only 15% black spots. Usually the spots are retained and the feathers that come from them are colored, but in this line most of the spots seem to be reduced and disappear so that only a feather or two were colored on these birds. Something in this line was enhancing the effect of dominant white.
Broilers may be a special case because there has been heavy selection for white plumage, but I'd suspect that the selection hasn't been any higher than in show stocks.
By Anonymous on Wednesday, December 5, 2001 - 03:25 pm:
spots on the heterozygotes, Rokimoto. You must
be younger than I, since you weren't at the U of A
when i was in graduate school there
(Mathematics). I have two nieces in undergrad
school there (Fayetteville) now. My X-sister-in-law
dated Don Tyson for a while (25 years ago)... it
didn't work out! (I thought I heard he died, but I
can't swear to that ... ). When I was at the U of A,
they were going to tear down Old Main until the
alumi objected, then the admin went on a
campaign to raise restoration funds ... they even
extored money from us grad students..... for shame
... grad students are nothing but slaves anyway....
(Right after I started grad school there, a fraternity
'took over' the administration building and called
the Gov. office (Governor Bill Clinton) to say that
they were seceeding from the Union!!! LOL!
needless to say that fraternity was disbanded for
some time....)
In our F1 generation, we have two pullets that are
completely black.... the dominant white didn't
express at all. The proportion is too small
statistically to be due to a female dam (Leghorn)
that isn't really homozygous for dominant white. I
have attributed this to the 'incompletely dominant'
character of the dominant white allele. I did
include her in the F1 set of dams.
I'm really looking forward to seeing how our F2
generation pullets lay.