Null alleles or genes have been studied in different organisms from the red pines of Minnesota to
Drosophila melanogaster and mice. Null alleles are difficult to identify because a heterozygous individual for one null allele and one active allele is phenotypically indistinguishable from a homozygous individual with both active alleles. In other words, a null allele can only be identified from the phenotypic standpoint if the individual is homozygous for the null allele. Researchers have been able to work around this problem by using detailed
Electrophoresis, gel assays, and chromosomal manipulation. • Allendorf et al. studied the enzyme activity of the same species of red pine seeds collected from two different tree stands in Minnesota. The two groups of trees were treated as one population because no deviations from expected genotype frequencies were observed, as would be expected if the populations were diverging from one another. Alleles that produced an enzyme lacking catalytic activity were denoted as null alleles. A total of 27 loci were tested in red pines and null alleles were found at 3 of those loci. Both experiments used the process of mutageneis, whereby the genetic content of the organism is changed, to produce individuals with different combinations of null mutations. ==See also==