Post by Darren Lim on Mar 10, 2004 2:06:00 GMT -5
We hear about the lethal factor when breeding chinchillas.
Do not breed a white chinchilla to any other type of white chinchilla.
Do not breed a velvet chinchilla to any other type of velvet chinchilla.
What does it mean?
A lethal is the result of a defective gene that causes a disturbance in the development of the growing organism that then causes it to die. There are many different kinds of lethals. They occur in any species, even humans (ex. cystic fibrosis). Lethals occur in either a heterozygous (single gene) or homozygous (double gene) state. A heterozygous lethal only requires one copy of the gene to cause a problem and that problem rarely allows the organism to reach sexual maturity, so the gene cannot be passed and dies out in the first generation. It is the homozygous lethal that we have to monitor because these genes can function in a heterozygous or "carrier" state.
Which chinchillas have a known lethal factor?
Of the mutation colors associated with chinchillas, only dominant white and domianant black (velvet) chinchillas have a lethal factor associated with their genotypes or genetic makeup. These lethals only occur in the homozygous state, so there are no homozygous whites or velvets. All whites and velvets are then heterozygous for those genes. They are unaffected by the lethal because the affected genes are paired with normal genes that act as backups for those functions that the affected genes cannot perform. Keep in mind that the white and velvet lethals are two different kinds of lethals and perform separately from each other. If you breed a white chinchilla to a velvet chinchilla, there is no lethal. It is when we breed two whites or two velvets that two of the same genes may combine in the offspring and cause the lethal.
Are we even sure these lethals exist in chinchillas?
During the early development of both the white and velvet chinchilla, breeders attempted to breed animals that were homozygous for these genes. A chinchilla that is homozygous for a gene will always pass that gene to its offspring and so has a lot of value in a breeding program, but all chinchillas proved to be heterozygous by producing normal-colored offspring. It was clear that no homozygous animals were being born. Reviewing the productivity of those animals also indicated that production went down when white x white or velvet x velvet were bred. When those same animals were switched to dissimilar partners, production went up and more babies were born. It was then suggested that the white and velvet genes were linked to a lethal factor.
So what happens when a lethal is present?
Most lethals are known to cause death in the early embryonic (or pre-embryonic) stage, resulting in a lack of production because fewer babies are born. The embryos are reabsorbed by the mother. Scientific evidence in both mice and rats supports this theory. No studies have been done on chinchillas (none that the author has been able to find and verify), but this is what breeders assume happens in the case with both the white and velvet chinchillas.
-cont-
Do not breed a white chinchilla to any other type of white chinchilla.
Do not breed a velvet chinchilla to any other type of velvet chinchilla.
What does it mean?
A lethal is the result of a defective gene that causes a disturbance in the development of the growing organism that then causes it to die. There are many different kinds of lethals. They occur in any species, even humans (ex. cystic fibrosis). Lethals occur in either a heterozygous (single gene) or homozygous (double gene) state. A heterozygous lethal only requires one copy of the gene to cause a problem and that problem rarely allows the organism to reach sexual maturity, so the gene cannot be passed and dies out in the first generation. It is the homozygous lethal that we have to monitor because these genes can function in a heterozygous or "carrier" state.
Which chinchillas have a known lethal factor?
Of the mutation colors associated with chinchillas, only dominant white and domianant black (velvet) chinchillas have a lethal factor associated with their genotypes or genetic makeup. These lethals only occur in the homozygous state, so there are no homozygous whites or velvets. All whites and velvets are then heterozygous for those genes. They are unaffected by the lethal because the affected genes are paired with normal genes that act as backups for those functions that the affected genes cannot perform. Keep in mind that the white and velvet lethals are two different kinds of lethals and perform separately from each other. If you breed a white chinchilla to a velvet chinchilla, there is no lethal. It is when we breed two whites or two velvets that two of the same genes may combine in the offspring and cause the lethal.
Are we even sure these lethals exist in chinchillas?
During the early development of both the white and velvet chinchilla, breeders attempted to breed animals that were homozygous for these genes. A chinchilla that is homozygous for a gene will always pass that gene to its offspring and so has a lot of value in a breeding program, but all chinchillas proved to be heterozygous by producing normal-colored offspring. It was clear that no homozygous animals were being born. Reviewing the productivity of those animals also indicated that production went down when white x white or velvet x velvet were bred. When those same animals were switched to dissimilar partners, production went up and more babies were born. It was then suggested that the white and velvet genes were linked to a lethal factor.
So what happens when a lethal is present?
Most lethals are known to cause death in the early embryonic (or pre-embryonic) stage, resulting in a lack of production because fewer babies are born. The embryos are reabsorbed by the mother. Scientific evidence in both mice and rats supports this theory. No studies have been done on chinchillas (none that the author has been able to find and verify), but this is what breeders assume happens in the case with both the white and velvet chinchillas.
-cont-