Final answer:
The correct term for a preexisting allele changed to a new version that does not code for a functional protein is a 'recessive' allele. The correct answer is option 2.
Step-by-step explanation:
When a preexisting allele is changed to a new version that no longer codes for a functional protein, the new allele is called a recessive allele. This term refers to an allele that causes a phenotype only seen in homozygous genotypes and never in heterozygous genotypes. A recessive allele will not be expressed in the presence of a dominant allele, which is an allele that can be manifested in the heterozygous state. This is in contrast to dominant alleles, which are observable even when only one copy is present.
Moreover, alleles can be recessive lethal when they are only lethal in the homozygous form, and non-lethal in the heterozygous state. This pattern of inheritance indicates that carriers of a lethal recessive allele can live normally and only show the severe effects of this allele when an individual inherits two copies, one from each parent. If two carriers have children, there is a 25% chance that the child will inherit both recessive alleles and manifest the associated condition, potentially leading to early mortality due to the essential nature of the gene affected.
Therefore, the correct option to fill in the blank is option 2) Recessive.