Nullalleelit

Nullalleelit, also known as null alleles or amorph alleles, are genetic variants that result in a complete loss of function for the gene they are located in. This means that no functional protein is produced from the DNA sequence. Nullalleelit can arise from various mutations, such as deletions that remove the entire gene, frameshift mutations that alter the reading frame and lead to premature termination codons, or nonsense mutations that introduce a premature stop codon. These mutations effectively render the gene non-functional.

The phenotypic consequences of a nullalleeli depend on whether the gene is essential for survival and whether the organism is diploid, meaning it has two copies of each gene. In a diploid organism, if one copy of the gene is functional and the other is a nullalleeli, the organism may still exhibit a normal phenotype if the functional copy produces enough protein to compensate. This is known as haplosufficiency. However, if the gene is haploinsufficient, meaning one functional copy is not enough, or if both copies of the gene are nullalleelit, the organism will display the full effects of the gene's absence. This can lead to a wide range of traits, from subtle changes to severe developmental abnormalities or lethality. In some cases, nullalleelit can be used in genetic research to study the function of a particular gene by observing the effects of its complete absence.