Eva's Mouse Genetics Page
- Lethal and Semilethal Genes

Denna sida på svenska. Some of the genes that gives the mouse its common colours or markings also makes the mouse sick, or unfit to live. These genes are called semilethal or lethal.

But how can this happen? I often hear people asking about the possibility of breeding out these diseases from a line of special mice. If you read a book about genetics (I have been reading "Modern Genetics", second edition, by Fransisco J. Ayala and John A. Kiger, Jr) you might find the clue.

Pleitrophy

Pleitrophy is when a certain gene affects more than one trait. So I found that the answer to the question "how can this happen?" is pleitrophy. Let's look at a list of some common colour and marking genes of the mouse.

Well known mouse diseases caused by colour genes:

• Dominant Yellow (A^Y), or Lethal Yellow as it is also called. Besides giving the mouse a lovely red or yellow colour this gene also have a less desireable effect. Any mouse which is homozygous for this gene dies early on the sixth day of gestation. The exact cause to how this happens is not known. But this means that this gene is a homozygous lethal.

• Albino (c). This gene directly makes the mouse lack all pigment. The pigment cells are normal, but the pigment is not there. An albino do not have as good eye vision as a non albino. There is also a behaviour difference between albinos and non albinos, to the effect that albinos are less active in certain specific situations than non albinos.

• Brindle (Mo^br). Brindle males usually dies between 10 and 14 days of age. Extremely few lives long enough to sire a litter. Brindle males suffer from a neurological impairment, as do homozygous females. This is characterized by a slight tremor and uncoordinated gait.

• Piebald (s). This gene is responsible for Dutch, Even, Broken and and partly for Dark Eyed White. These animals, not only having spots of no pigment in the fur, also may have spots of no pigment internally. Furthermore, the gene s is also associated with megacolon. As many as 10% of the ss mice might die from this disease. Megacolon in ss mice is associated with a marked reduktion of myenteric ganglion cells. When the mouse gets sick the colon gets distended and filled with fecal matter. There is no cure to this disease.
  

• Dominant White (W), or Dominant Spotting as it is also called. This gene is associated with congenital anemia. WW mice dies within a few days after birth from anemia. Which means that this gene is a homozygous lethal.

• Rump-White (Rw). A homozygous lethal, where RwRw embryos dies in mid-pregnancy.

Copyright Eva Johansson.
Last update: 3rd of December 2007.