  We have used the sexual Penna ageing model to show that the relation between
dominance and recessiveness could be a force which optimizes the genome size.
While the possibility of complementation of the damaged allele by its
functional counterparts (recessiveness) leads to the redundancy of genetic
information, the dominant effect of defective genes tends to diminish the
number of alleles fulfilling the same function. Playing with the fraction of
dominant loci in the genome it is possible to obtain the condition where the
diploid state of the genome is optimal. If the status of each bit position as
dominant or recessive mutations is changed for each individual randomly and
rarely, then after a long time a stationary equilibrium of many recessive and
few dominant loci is established in the sexual Penna model. This effect
vanishes if the same changing distribution of dominant loci applies to all
individuals.
