In this chapter, we have focused on sex differentiation, sex chro-
mosomes, and genetic mechanisms involved in sex determination. At the same
time, 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, you should answer the following fundamental questions:
(a) How do we know that in humans the X chromosomes play
no role in sex determination, while the Y chromosome causes maleness and its
absence causes femaleness?
(b) How did we originally (in the late 1940 s) analyze the sex ratio at
conception in humans, and how has our approach to studying this issue changed
in \(2015 ?\)
(c) How do we know that \(X\) chromosomal inactivation of either the paternal or
maternal homolog is a random event during early development in mammalian
females?
(d) How do we know that Drosophila utilizes a different sexdetermination
mechanism than mammals, even though it has the same sex-chromosome
compositions in males and females?