Inference of allelic dosages and inheritance modes in tetraploids: a case study in Betula apoiensis with a putative hybrid origin

In tetraploids, inference of allelic dosages and inheritance modes is difficult due to the ambiguous number of allele copies and the variation between disomic and tetrasomic patterns. Considering the biases of amplification and the overlaps of stutter products in polymerase chain reactions, we inferred tetraploid genotypes at three nuclear microsatellite loci in progeny arrays from six reciprocal crosses among three parents of Betula apoiensis with a putative hybrid origin. In each cross, we assigned diploid genotypes to gametes on the basis of the tetraploid genotypes of the parents and their progeny and observed the frequencies of the gamete genotypes. Segregation patterns of the observed gamete genotypes indicated few null alleles in the progeny arrays and tetrasomic inheritance with rare double reduction. This mode of inheritance was consistent between genders and between mates in the crosses. This result suggests that our method to infer tetraploid genotypes in nuclear microsatellites is successful in family samples with few null alleles when the amplification biases and the stutter-product overlaps are accessed properly.