Chapter 8, Problem 1PDQ

HOW DO WE KNOW? In this chapter, we have focused on chromosomal mutations resulting from a change in number or arrangement of chromosomes. In our discussions, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions?

1. (a) How do we know that the extra chromosome causing Down syndrome is usually maternal in origin?
2. (b) How do we know that human aneuploidy for each of the 22 autosomes occurs at conception, even though most often human aneuploids do not survive embryonic or fetal development and thus are never observed at birth?
3. (c) How do we know that specific mutant phenotypes are due to changes in chromosome number or structure?
4. (d) How do we know that the mutant Bar-eye phenotype in Drosophila is due to a duplicated gene region rather than to a change in the nucleotide sequence of a gene?