4. hemophilia is an inheritable genetic disorder that prohibits the proper formation of blood clots. the recessive gene that causes hemophilia is located on the x-chromosome. given this information, which of the following statements is true?
a. in order for a male offspring to be a hemophiliac, his mother must be a hemophiliac.
b. in order for a female offspring to be a hemophiliac, her father must be a hemophiliac.
c. in order for a male offspring to be a hemophiliac, his father must be a hemophiliac.
d. in order for a female offspring to be a hemophiliac, her mother must be a hemophiliac.

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

Why do leaves change color in the fall? green pigments break down and no longer mask the color of chlorophyll. chlorophyll breaks down and no longer masks the colors of other pigments. red- and yellow-colored pigments grow and mask green-colored chlorophyll. green-colored chlorophyll breaks down and turns red and yellow.

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.