Why does the heterozygote mice survive even though it has a dominant lethal gene?

In mice, the lethal gene is dominant and it codes for yellow fur. The recessive gene codes for grey fur. According to various sources, even though the lethal gene is dominant, but the heterozygote of this gene does not cause the mice to die.Why does the heterozygote mice survive even though it has a dominant lethal gene?
The simple answer is that the Agouti yellow lethal gene (Ay) is pleiotropic. It is dominant with respect to yellow color and certain other phenotypes, but not dominant with respect to lethality because it is only lethal in a homozygous condition. Further, it is not specifically the Ay allele that is the lethal gene, but a closely linked gene that is disrupted by a small deletion that causes the Ay allele. It is confusing, but the adjective dominant in the phrase dominant yellow lethal, only refers to yellow (dominant yellow) and it is just understood by people working in the field that the gene is dominant yellow and is homozygous lethal, so in basic genetics terms, it is dominant with respect to yellow, but not with respect to lethality. However, rather than worry about the dominant or recessive nature of the mutation, researchers have gone on to characterize the mutation and it appears to be a small deletion that causes disruption of another gene (Raly), that is normally required expressed and if the mutation is homozygous results in preimplantation lethality.





Here are a couple of websites that explain further:





http://www.ndsu.edu/instruct/mcclean/pls鈥?/a>





http://www.pubmedcentral.nih.gov/picrend鈥?/a>





http://www.genesdev.org/cgi/content/abst鈥?/a>





Hope this helps!Why does the heterozygote mice survive even though it has a dominant lethal gene?
Because the mouse is heterozygous.





Heterozygous organisms posess gene pairs consisting of a dominant and a recessive gene. The dominant gene expresses some characteristic, even if paired with a recessive gene. Basically, this term is just a fancy way of calling something a ';hybrid';.





The lethal gene codes for yellow fur, but is not lethal unless both genes code for yellow fur. This is known as a homozygous individual, since both genes are identical. Most people call these ';pure strains'; because all their offspring always express the same traits. Hybrids (heterozygotes) will not ';breed ture';.





The heterozygous mouse has yellow fur because the fur color gene is dominant. However, the particular gene sequence which is lethal is not domant and must pair with an identical gene sequence before this trait is expressed. Many genetic disorders are due to recessive traits.