Final answer:
A lethal allele that is influenced by specific environmental conditions and leads to an organism's death is known as a lethal allele, which can be either recessive or dominant. Recessive lethal alleles cause death when present in two copies, while dominant lethal alleles can cause death in both homozygous and heterozygous states, such as with Huntington's disease.
Step-by-step explanation:
An allele that leads to the death of an organism only under specific environmental influences would be called a lethal allele. These alleles can be either recessive or dominant. A recessive lethal allele is only fatal in the homozygous state, while heterozygotes may be carriers or have some altered, non-lethal phenotype. For example, Tay-Sachs disease is caused by a recessive lethal allele where both parents are carriers, resulting in the disease manifesting in the progeny who inherit two copies of the allele.
On the other hand, a dominant lethal allele can lead to death both in homozygous and heterozygous states. However, they are rare and could remain in a population if the onset of lethality occurs after reproductive age, allowing it to be unknowingly passed on to the next generation. A well-known example of a dominant lethal allele is the one causing Huntington's disease, where individuals who inherit just one copy of the mutated allele will eventually develop the disease, often later in life after they've had children.