This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic and genetic disorders, Subject name: Pediatrics
In an Autosomal Recessive (AR) disorder, one parent is normal and the other is carrier and the child is also affected. What is the reason 
Select and explain. 
A. Germ line mosaicism, B. Genomic imprinting, C. Penetration, D. Uniparental disomy
D: Uniparental disomy
Answer: D: Uniparental disomy 
Explanation: Uniparental disomy refers to the situation in which 2 copies of a chromosome come from the same parent, instead of 1 copy coming from the mother, and 1 copy coming from the father. Angelman syndrome (AS) and Prader-Willi syndrome (PWS) are examples of disorders that can be caused by uniparental disomy. Reference: GHAI Essential pediatrics, 8th edition