<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 3500-g 7 lb 11 oz healthy female newborn is delivered at 38 weeks gestation. Chorionic villus sampling CVS in the first trimester showed a trisomy of chromosome 21 but the pregnancy was otherwise uncomplicated. Physical examination of the newborn is normal. Chromosomal analysis at birth shows a 46, XX karyotype. Which of the following is the most likely explanation for the prenatal chromosomal abnormality?? A: Maternal disomy, B: Phenotypic pleiotropy, C: Incomplete penetrance, D: Variable expressivity, E: Placental mosaicism,  <response>: This is a question about prenatal testing that showed trisomy 21 Down syndrome but the newborn has a normal karyotype. The choices describe different genetic phenomena. Maternal disomy is when both chromosomes come from the mother rather than one from each parent. Phenotypic pleiotropy is when a single gene affects multiple phenotypic traits. Incomplete penetrance is when a genotype does not always result in the expected phenotype. Variable expressivity is when a genotype results in different phenotypes in different people. Placental mosaicism is when some cells in the placenta have a chromosomal abnormality but the fetus is normal.Based on the information provided, placental mosaicism seems the most likely explanation for the discrepancy between the prenatal test and the newborns normal karyotype. The prenatal test on chorionic villi sampled placental tissue which may have contained abnormal trisomic cells, while the newborns own cells were normal.E: Placental mosaicism 