Mode of Inheritance A

“Non-disjunction” is the main cause of trisomy 13. Non-disjunction is an error in cell division—mitosis or meiosis—that results in a cell with an abnormal number of chromosomes. Consequently, one daughter cell will have too many chromosomes, and one will have an absence of chromosomes. If a non-disjoined reproductive cell is present in fertilization, the offspring will have an uneven amount of chromosomes in their genotype. In Patau syndrome, the sex cell has too much of the chromosome during fertilization.


Mode of Inheritance B

However…it is not impossible for trisomy 13 to be inherited. An unaffected parent can carry a rearrangement of genetic material, called a balanced translocation, between chromosome 13 and another chromosome. Balanced translocations are “balanced,” because there is no extra genetic material in the cell. However, a person with a balanced translocation, involving chromosome 13, has an increased chance of passing on extra material from that chromosome to their children, creating an imbalanced translocation.