What does the term "embryonic lethal" refer to in genetics?

The term "embryonic lethal" specifically refers to an allele that leads to the death of the embryo during development. When an organism carries such an allele, it typically results in the failure of the embryo to survive to a stage where it could be born or hatch. This is significant in genetics as the presence of embryonic lethal alleles affects the inheritance patterns observed in a population, as offspring that inherit these alleles do not survive.

In the context of the other options, the second option relates to traits that are visible in the phenotype of adult organisms but does not describe a lethality aspect. The third option mentions a dominant phenotype; however, for an allele to be classified as embryonic lethal, it specifically means that embryos do not survive regardless of their phenotypic expression. Therefore, the correct definition of "embryonic lethal" is aligned with it being an allele that causes embryo death.