Mutations that result in no gene product or totally nunfunctional gene products are called:
a. isomers
b. isoalleles
c. null alleles
d. lethal alleles
e. forward alleles

c. null alleles

Explanation:

Genetic mutation can produce a non functional allele called as null allele. There might not be any product from this allele or a defective product might be produced. If the mutant allele does not even produce a RNA transcript, it is called as RNA null. If it is not able to produce the final protein product, it is called a protein null.

An example of null allele is The O blood group. Due to a mutation in the gene producing A antigen, an enzymatically inactive protein is produced by O blood group people. Both the copies of null allele O are required for O phenotype to be present.  

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