I need to admit that tragedies can often be very interesting. Lethal Genes, tragic as its name suggests, are genes whose phenotypes lead an organism to unconditional death. Death can sometimes not be immediate and take years or even decades. The notion that carriers of lethal genes cannot leave offspring is therefore false; for instance, the notorious Huntington's disease, inherited as an autosomal dominant condition, usually manifests itself when the patient ages over 40, enabling itself to clandestinely pass down to the patient's descents.
Lethal genes were first discovered by Lucien Cuenot, a French biologist. Cuenot observed unusual genetic patterns while studying inheritnce of a coat color gene in mice. The offsprings of two yellow mice, quite surprisingly, always showed a 2:1 ratio instead of a conventional Mendelian 3:1. The mice happened to never produced a single homozygous yellow mouse. Five years later, W.E. Castle and C.C. Little confirmed the existence of lethal gene by showing that one-quarter of the offspring from crosses between heterozygotes die during embyonic development.
When an allele causes lethality, this is evidence that the gene must have a critical function in an organism. The discoveries of many lethal alleles have provided information on the functions of genes during development. Additionally, scientists can use conditional and synthetic lethal alleles to study the physiological functions and relationships of genes under specific conditions.
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