Chapter 13 - Chromosomes, Mapping, and the Meiosis-Inheritance Connection - Review Questions - Apply - Page 255: 3

C.

In trisomies, the extra copy of a chromosome has its genes expressed, imbalancing the cell and, thus, development. Chromosome 21 is much smaller than most other human chromosomes, and so the extra copy in Down Syndrome causes much less disruption. A. says, in part, the opposite of this and is, thus, wrong, while B. and D. are simply not true.