A recessive allele of the mouse agouti locus showing lethality with yellow, Ay

The radiation-induced agouti allele a1 is recessive to the alleles a and a4H (which resembles ae). It is lethal when homozygous and also in combination with the dominant yellow allele Ay. The ethylnitrosourea induced allele a16H is also lethal when homozygous, and when heterozygous with a shows a phenotype like that of ax, with black back and lighter belly. Like ax it is not lethal with Ay, and it is also not lethal with a1, a1 is believed to be the first recessive allele which is lethal with Ay, and may be useful in elucidating the complexity of the agouti locus.