Suppose pcr is used to amplify a single dna marker on human chromosome 21. this is a way to identify individual chromosomes, such as paternal and maternal chromosome 21 from each parent. further suppose that a couple who have a child with down syndrome (trisomy 21) is examined for this marker. the mother has marker alleles of 310 and 380 bp. her mate has marker alleles of 290 and 340 bp. what combinations of pcr bands would be expected in their child with down syndrome if nondisjunction occurred in a. maternal meiosis i b. maternal meiosis ii c. paternal meiosis i d. paternal meiosis ii