A gene whose phenotypic effect kills the bearer is called
A. Lethal
B. Pleiotropic
C. Supplementary
D. Complementary

Hint: Gene is nothing but a sequence of nucleotides that are found in DNA or RNA, this gene which encodes for the synthesis of particular things such as proteins, and in the process of gene expression, the DNA is copied to RNA, where it can be directly expressed as a phenotypic trait.

Complete answer:
The genes whose phenotypic effect kills the bearer are called lethal genes, and these are the genes that cause the death of the organism that carries them, and they usually result from a mutation in genes, where that is essential for growth and development.
These lethal genes may be dominant, recessive, and conditional types.
Recessive lethal genes are a pair of identical genes that both are present in an organism that ultimately results in the death of the organism, which is referred to as recessive lethal genes.
Though the recessive lethal genes, it may code for dominant or recessive, they only expressed in homozygous condition. And the heterozygous may display a form of phenotype.
> Dominant lethal genes are the one where even one copy of these genes in an organism is fatal, and these genes are not commonly found in the population because they usually result in the death of an organism, before it transmits that gene to offspring.
> Conditional lethal genes are the only fatal if any environmental factors add up to this lethal gene.
Whereas complementary genes are present on different gene locus but interact with each other to express a single character in combination.
While the supplementary genes are one which includes two pairs of non allelic genes, where combined involvement only results in the expression of character.

So the correct option is A.

Note: The question is about the gene that kills the bearer, when looking at the options, the first one is lethal, which mean that it is fatal or harmful or causing death, so the answer is lethal, where the remaining options say about different types of genes that are responsible for phenotypic expression based on their combination and location.