<unk>  can occur as a random event during the formation of egg cells or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue. *When the child receives two (different) homologous chromosomes (inherited from both grandparents) from one parent, this is called heterodisomic<unk> . Heterodisomy (heterozygous) indicates a meiosis I error if the gene loci in question didn't cross over. *When the child receives two (identical) replica copies of a single homologue of a chromosome, this is called an isodisomic<unk> . Isodisomy (homozygous) indicates either a meiosis II (if the gene loci in question didn't cross over) or postzygotic chromosomal duplication. *A meiosis I error can result in isodisomic<unk>  if the gene loci in question crossed over, for example, a distal isodisomy would be due to duplicated gene loci from the maternal grandmother that crossed over and due to an error during Meiosis I, ended up in the same gamete. *A meiosis II error can result in heterodisomy<unk>  if the gene loci crossed over in a similar fashion.
Uniparental disomy
Genomic imprinting
Germline mosaicism
Structural inheritance
Postzygotic mutation
Robertsonian translocation
Caudal duplication
Non-Mendelian inheritance