The human sex chromosomes are of the XX-XY pattern. The Y chromosome is
much smaller than the X chromosome. Two types of sperm cells are formed during
gametogenesis; half of these have the X chromosome and the others have the Y
chromosome. Every egg cell has an X chromosome; therefore, fertilization determines the
sex. If a Y sperm cell fertilizes the egg a male develops.
2. The author's purpose is to
a. explain how the sex of humans is determined.
b. describe chromosomes.
c. tell the steps in fertilization.
d. contrast X and Y chromosomes