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This bird is what is called a "halfsider" and the condition is not capable of being transmitted to further offspring. It is a random event not caused by genes but (probably, see below) a mistake in cell-division very early in development (when the organism is only at the few-cell stage). Yes, I know this is in different species, but the principle doesn't change.
http://www.budgerigars.co.uk/genetics/halfside.html
http://www.euronet.nl/users/hnl/halfside.htm
http://www.google.com/images?q=half...ZGI_rgQeco5HJCw&ved=0CDgQsAQ&biw=1280&bih=621
So while one article proposes nerve damage as the origin of halfsiders, other people believe it is the result of a mosaic condition. Here's the simplified explanation:
We start out as one cell (a fertilized egg). That one cell undergoes mitosis (copying and division) to become many cells. Sometimes there is an error in the division, and if that error doesn't kill one of the cells, the error will be passed down to all descendants of that cell. Imagine you have a one-page document. You make copies on a xerox machine, but not in the conventional way -- you do one at a time. Take the original, scan it, make one copy. Then take the copy and make a mark on it. Now make another copy of the original, and a copy of the marked copy. Continue making one copy of each sheet of paper you have. Soon, you'll have a lot, and you'll notice that half of them have a mark from that first copy. Same thing happens with the cells -- they maintain that original copying error down the line. In the organism, cells begin to occupy distinct positions and start forming something of a definite shape. Now the copies with the mark may be all on one side, and the copies without the mark on the other. The organism continues to grow, develops, and is born/hatched. If the original copying-error affects a gene (or whole chromosome) that affects coloration, you will see a difference from one side to the other.
This "halfsider" will not be able to pass on the "halfsider" condition because it is not something caused by genes. Some halfsiders are sterile (look up gynandromorph) because the "left side vs right side" is not just a difference in color, but a difference in gender (male left side, female right side, or vice versa). Only in species which are sexually dimorphic (boys and girls look different) is this apparent. Quite striking examples can be found in Eclectus parrots, where boys are green and girls are red/blue. Gynandromorph halfsider Eclectus parrots will be green on one side, and red on the other.
There are other, more common, forms of mosaicism. A great example is calico or tortoiseshell cats. Remember that in mammals, it is the male who has the different sex chromosomes, and the female has two of the same (males XY, females XX). Only one X chromosome is required for life functions, so in females, the other must be mostly "turned off." So, at a certain cellular stage after an egg is fertilized (I don't remember which stage, but it is much further along than the "halfsider" moment), one of the female's X chromosomes is mostly inactivated. Determining which X chromosome is completely random, but all cells descending from those cells will maintain the same X inactivation. So let's say one cell inactivates the X from mom -- all cells descended will have mom's X inactivated.
In cats, the red and black color alleles (same gene, different versions) are located on the X chromosome. This is why calico (red, black and white) or tortoiseshell (red and black) cats are (almost) always female, because in order to have both alleles (red and black), they need to have two X chromosomes. The rare males that are tortoiseshell or calico usually result from being XXY and are often sterile.
OK, so now look at a calico cat. One of her parents carried black, the other carried red. Let's say Dad was black and Mom was red. The calico gets one X from each. Early on in development, one X is randomly chosen for inactivation, and then development continues. When you see the patches of red and black, you can see which X was inactivated. The red patches arose from cells in which Dad's X was inactivated (black turned off, red turned on), and the black patches arose from cells in which Mom's X was inactivated (red turned off, black turned on). This is why distribution of red/black color in calico cats is impossible to breed for. This is also why, a few years back, the first cloned cat looked different from the original. WHY they picked a calico cat is beyond me, but the cloned offspring was not calico. Why? Because, as I mentioned earlier, whichever X is inactivated will be maintained by all future mitotic descendants of that cell. Take a tissue sample from a "black" region and the whole clone will have red turned off, even though genetically it is still calico (has one red and one black allele). And that's what happened. Oh, and the white spots in calico are controlled by a separate gene for white spotting.
The point of the whole thing is that when you see some sort of mosaic individual, the mixed pattern results from cellular differences, not a new kind of "pied."
~Christopher
This bird is what is called a "halfsider" and the condition is not capable of being transmitted to further offspring. It is a random event not caused by genes but (probably, see below) a mistake in cell-division very early in development (when the organism is only at the few-cell stage). Yes, I know this is in different species, but the principle doesn't change.
http://www.budgerigars.co.uk/genetics/halfside.html
http://www.euronet.nl/users/hnl/halfside.htm
http://www.google.com/images?q=half...ZGI_rgQeco5HJCw&ved=0CDgQsAQ&biw=1280&bih=621
So while one article proposes nerve damage as the origin of halfsiders, other people believe it is the result of a mosaic condition. Here's the simplified explanation:
We start out as one cell (a fertilized egg). That one cell undergoes mitosis (copying and division) to become many cells. Sometimes there is an error in the division, and if that error doesn't kill one of the cells, the error will be passed down to all descendants of that cell. Imagine you have a one-page document. You make copies on a xerox machine, but not in the conventional way -- you do one at a time. Take the original, scan it, make one copy. Then take the copy and make a mark on it. Now make another copy of the original, and a copy of the marked copy. Continue making one copy of each sheet of paper you have. Soon, you'll have a lot, and you'll notice that half of them have a mark from that first copy. Same thing happens with the cells -- they maintain that original copying error down the line. In the organism, cells begin to occupy distinct positions and start forming something of a definite shape. Now the copies with the mark may be all on one side, and the copies without the mark on the other. The organism continues to grow, develops, and is born/hatched. If the original copying-error affects a gene (or whole chromosome) that affects coloration, you will see a difference from one side to the other.
This "halfsider" will not be able to pass on the "halfsider" condition because it is not something caused by genes. Some halfsiders are sterile (look up gynandromorph) because the "left side vs right side" is not just a difference in color, but a difference in gender (male left side, female right side, or vice versa). Only in species which are sexually dimorphic (boys and girls look different) is this apparent. Quite striking examples can be found in Eclectus parrots, where boys are green and girls are red/blue. Gynandromorph halfsider Eclectus parrots will be green on one side, and red on the other.
There are other, more common, forms of mosaicism. A great example is calico or tortoiseshell cats. Remember that in mammals, it is the male who has the different sex chromosomes, and the female has two of the same (males XY, females XX). Only one X chromosome is required for life functions, so in females, the other must be mostly "turned off." So, at a certain cellular stage after an egg is fertilized (I don't remember which stage, but it is much further along than the "halfsider" moment), one of the female's X chromosomes is mostly inactivated. Determining which X chromosome is completely random, but all cells descending from those cells will maintain the same X inactivation. So let's say one cell inactivates the X from mom -- all cells descended will have mom's X inactivated.
In cats, the red and black color alleles (same gene, different versions) are located on the X chromosome. This is why calico (red, black and white) or tortoiseshell (red and black) cats are (almost) always female, because in order to have both alleles (red and black), they need to have two X chromosomes. The rare males that are tortoiseshell or calico usually result from being XXY and are often sterile.
OK, so now look at a calico cat. One of her parents carried black, the other carried red. Let's say Dad was black and Mom was red. The calico gets one X from each. Early on in development, one X is randomly chosen for inactivation, and then development continues. When you see the patches of red and black, you can see which X was inactivated. The red patches arose from cells in which Dad's X was inactivated (black turned off, red turned on), and the black patches arose from cells in which Mom's X was inactivated (red turned off, black turned on). This is why distribution of red/black color in calico cats is impossible to breed for. This is also why, a few years back, the first cloned cat looked different from the original. WHY they picked a calico cat is beyond me, but the cloned offspring was not calico. Why? Because, as I mentioned earlier, whichever X is inactivated will be maintained by all future mitotic descendants of that cell. Take a tissue sample from a "black" region and the whole clone will have red turned off, even though genetically it is still calico (has one red and one black allele). And that's what happened. Oh, and the white spots in calico are controlled by a separate gene for white spotting.
The point of the whole thing is that when you see some sort of mosaic individual, the mixed pattern results from cellular differences, not a new kind of "pied."
~Christopher
