Figure 5. Precocious separation of sister chromatids without alleles exchanged during meiosis I
The diagram illustrates the four possibilities of segregation during meiosis I and then the 24 possibilities of segregation during the second meiosis for every primary oocyte. Twelve ova correspond to an euploidy rescue, which lead a normal euploid zygotes, eight disomic ova with an allelic pattern 1:1, which originate a trisomic zygotes with a 1:1:1 allelic pattern; and four also disomic but with a double dose of only one allele, which create a trisomic zygotes with a 2:1 allelic pattern.