| If you think of chromosomes as parking lots, for sets of
blueprints, then each chromosome has a number of distinct "parking spots"
where a particular set of blueprints is assigned to park. A parking
spot is known as a "locus" (location) on a
chromosome, and the set of blueprints is called a "gene."
Mostly, animals and people have chromosomes that come in pairs, so they
get TWO of any gene (i.e., two identically shaped parking lots). The
one exception to this is the sex chromosome pair, where in that pair of
chromosomes, the two chromosomes have different shaped parking lots, and
one of the parking lots has more spaces than the other. Now, there
are different gene versions that can park in a given spot. Suppose
you had a parking lot where in spot #32 Ford Mustangs were allowed to
park. It could be a red Mustang or a blue one, but Ford Tauruses or
Chevy trucks could not park there. Ford Mustangs are all the same
MODEL, but come in different VERSIONS, just like genes. But a Ford
Taurus, or Chevy truck is a DIFFERENT MODEL, altogether. When a gene
comes in different versions, we call the versions "alleles."
So, a gene may have several different alleles, but it is different from a
separate gene. For example, the gene for eye color is a different
GENE than the gene for earlobe shape. But the allele of blue eye
color is the SAME GENE as the allele for brown eye color, but a different
VERSION of that SAME GENE.
The "E" locus in poultry controls the
"base color" of the bird (i.e., it is the parking spot assigned for the
blueprints for basic overall feather color). For example, the most
dominant version (allele) of an E-locus gene is called "E," (which,
coincidentally is the same overall name as the parking spot, so the
parking spot is called "E" and then the most dominant color allele of
the gene that parks there is also called "E" - a lot of times they name
the parking spot after the most "famous" allele that may park there)
which is solid black base color, doesn't allow any color to "bleed"
through. Then the next most dominant E-locus allele is called "ER,"
which gives rise to a mostly black bird with parts that are not black
such as head and hackles, saddles and parts of the flight feathers and
breast lacing on males, and head and hackles on females. There are
several more alleles that belong to the "E" locus, as well. (Wheaten,
white, etc.)
WHAT color shows on these parts is defined by a different gene, a secondary color gene (i.e., not the E-locus gene, but rather "S" locus gene, a different parking spot). So, in the case of a copper black bird versus a birchen bird, they are both ER allele at the E-locus (so display the same PATTERN of color distribution and basic overall color of black) but have different secondary color genes. In the case of the copper black, the color allele at the S location is gold ("s+" is the notation for the gold allele in poultry at that location, and "S" is the notation for silver - they are alleles that occupy the same "parking place" on the chromosome). Thus, a copper black bird is ER with s+s+(gold, in this case a coppery red version of gold), whereas a birchen is ER with SS(silver, which ideally is white).
Blue color is the result of a third
gene. It is a modifying gene for black pigment, and is located at a
parking spot called "Bl." The choices (alleles) that can go into this
parking spot are basically black pigment (bl+ = black pigment allele) or
a bleaching allele (Bl = blue allele, which really is the black pigment
allele with a modifier that bleaches the black pigment). If you think
of the blue allele (Bl) as a bleaching version, then you can visualize
how if a bird gets one dose of blue allele (Bl,bl+), it turns out blue
in color, and if a bird gets two doses of blue allele (Bl,Bl), it
gets double-bleached all the way to splash. And the blue allele acts
wherever there is black in the bird, so wherever the bird WOULD HAVE
BEEN BLACK, it is now bleached either to blue, or all the way to splash,
depending if it gets (one blue allele and one black pigment allele), or
(two blue alleles).
If you imagine that each parent has two cards in a deck of cards for a given gene, and can give only one card to an offspring, but it can be either card, then if mom has cards A and B in her deck and dad has cards C and D in his deck, then their children each get two cards, one from mom, and one from dad, for a given gene. So this mom and dad could have kids with AC or AD or BC or BD. (Where items in pink are what the kids get from mom, and items in orange are what kids get from dad, gene-wise) Take a second example. If mom had A and B and dad had A and B, then their kids could have AA, AB, BA, or BB. AB is the same as BA - it doesn't matter which gene came from mom and which from dad, if you get dealt an ace of spades from mom and a jack of hearts from dad, or if you get dealt a jack of hearts from mom and an ace of spades from dad, you still end up with the same cards. If you have a blue bird, then the genes are (bl+,Bl) in that bird, because it takes one black and one blue allele to get a blue bird. It takes two black alleles (bl+,bl+) to make the bird black. It takes two blue alleles (Bl,Bl) to make the bird splash. So:
So if you had a blue mother (bl+,Bl) and blue father (bl+,Bl), then the kids could be: (bl+, bl+), (bl+,Bl), (Bl, bl+), or (Bl, Bl). Since (bl+, Bl) and (Bl, bl+) are the same thing, then you would theoretically get from four kids one (bl+,bl+)=black kid, two (bl+,Bl)= blue kids, and one (Bl,Bl)= splash kid. So, 1/4 of the kids would be splash, 2/4 (or 1/2) of the kids would be blue, and 1/4 of the kids would be black.
So, breeding a blue bird to a blue
bird, regardless of OTHER color types (gold, lacing, etc.), you will
get 1/4 black, 1/2 blue, and 1/4 splash theoretically, wherever
that bird WOULD HAVE BEEN BLACK, otherwise. So, breeding a copper blue
rooster to a copper blue hen would theoretically result in 1/4 copper
BLACKS, 1/2 copper BLUES, and 1/4 SPLASH coppers.
Breeding a solid blue bird to a solid blue bird likewise would theoretically result in 1/4 solid blacks, 1/2 solid blues, and 1/4 solid splashes. Keep in mind that these ratios apply to large numbers of samples. It is entirely possible that you could hatch 12 offspring from a blue x blue mating, and get different ratios, because it is a statistically small sample. If you breed a black (bl+, bl+) bird to a blue (bl+,Bl) bird, you theoretically get: (bl+,bl+), (bl+,Bl), (bl+, bl+), and (bl+,Bl). Since (bl+,Bl) is the same hand dealt as (bl+,Bl), and since (bl+,bl+) is the same hand dealt as (bl+, bl+), then you would get two black kids and two blue kids for every four kids, in theory. If you breed a black (bl+, bl+) to a splash (Bl,Bl), then you would get (bl+,Bl), (bl+, Bl), (bl+,Bl) and (bl+,Bl) kids. Since (bl+,Bl) is the same as (bl+,Bl), and the same as (bl+, Bl) and same as (bl+,Bl), then you would get four blue kids. If you breed a black (bl+, bl+) bird to a black (bl+, bl+), you get all blacks. If you breed a splash (Bl, Bl) bird to a splash (Bl, Bl) bird, you get all splashes. If you are red/green colorblind, then you are insane by now, trying to read this. :)
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