The effectiveness of geographic barriers in promoting speciation is related most to
a. the size of the barrier.
b. the inability of the organisms to overcome the barrier.
c. the speed at which the barrier forms.
d. how long the barrier exists.
e. the size of the population it separates.
animal pole
Choose the one best answer for each numbered item.
a. visible marker of the site where an amphibian’s body axis will be established and
where gastrulation will begin
b. the formation of two or three embryonic tissue layers
c. the fusion of male and female nuclei
d. the entire body divides transversely; each half grows and regenerates the missing part
e. selective gene expression results in different cell types
f. subdividing of the zygote by mitosis; no growth occurs
g. region of zygote that has less yolk and is pigmented
h. an embryonic stage of development that has three primary tissue layers before
organogenesis begins
i. the formation of organs
j. one body part develops in response to signals from an adjacent part
k. the growth, shaping, and spatial coordination of tissues and organs so that a