Based on the Classic Experiments of Creighton and McClintock with Maize,crossing

Multiple Choice

Based on the classic experiments of Creighton and McClintock with maize,crossing over involves a physical exchange between chromatids.What particular chromosomal characteristic allowed their experiments to succeed?

A) a missing chromosome
B) a chromosome with a unique cytological marker
C) three chromosomes with identical structure
D) colored bands along the lengths of a chromosome
E) an extra chromosome