One of the reasons why it has been difficult to bring microevolutionary experiments into classrooms is the obvious tradeoff between choosing an allele that is strongly selected against, such as a lethal allele, and choosing one that is easy to visualize.
The expected frequency of flightless mutants was estimated according to discrete generation selection against a lethal allele (Crow & Kimura, 1970: eq.
Introduction of a
lethal allele into a feral mouse population.
Selection against
lethal alleles in females heterozygous for incontinentia pigmenti.
Lethal alleles in Mus musculus: local distribution and evidence for isolation of demes.
The dominance coefficients of slightly deleterious alleles have been estimated to be about 0.3, whereas
lethal alleles tend to be recessive (Simmons and Crow 1977; Johnston and Schoen 1995).
Model relating unsound seed and embryonic
lethal alleles in self-pollinated pines.
In this paper, we investigate two mechanisms that may help to explain these observations: (1) a high genomic mutation rate to recessive
lethal alleles, and (2) selective interference among loci with deleterious recessive mutations under partial selfing.
As noted by Werren and by Donald Waller, even
lethal alleles tend to have measurable effects on the fitness of their heterozygous carriers, but several other authors persist in stating that detrimental alleles are recessive.