Disclosed herein is a system and method for increasing the fidelity of measured genetic data, for making allele calls, and for determining the state of aneuploidy, in one or a small set of cells, or from fragmentary DNA, where a limited quantity of genetic data is available. Genetic material from the target individual is acquired, amplified and the genetic data is measured using known methods. Poorly or incorrectly measured base pairs, missing alleles and missing regions are reconstructed using expected similarities between the target genome and the genome of genetically related individuals. In accordance with one embodiment of the invention, incomplete genetic data from an embryonic cell are reconstructed at a plurality of loci using the more complete genetic data from a larger sample of diploid cells from one or both parents, with or without haploid genetic data from one or both parents. In another embodiment of the invention, the chromosome copy number can be determined from the measured genetic data of a single or small number of cells, with or without genetic information from one or both parents. In another embodiment of the invention, these determinations are made for the purpose of embryo selection in the context of in-vitro fertilization. In another embodiment of the invention, the genetic data can be reconstructed for the purposes of making phenotypic predictions.