During fertilization in humans, _______________________
(a) a wave of Ca2+ ions is released in the fertilized egg's cytoplasm.
(b) only one sperm binds to the unfertilized egg.
(c) a sperm moves in a random fashion until it encounters an egg.
(d) several sperm pronuclei compete in the cytoplasm to fuse with the egg nucleus.
Choice (a) is correct. Many sperm can bind to an egg [choice (b)]. Cells surrounding the egg release a chemoattractant signal, attracting the sperm to the correct place; sperm are moving toward the chemoattractant signal and not moving randomly [choice (c)]. Mechanisms exist to ensure that only one sperm fertilizes each egg, and thus only one sperm pronucleus will reach the cytoplasm of the egg [choice (d)].
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The excretory structures of terrestrial arthropods are slender projections from the digestive tract that are attached at the junction of the midgut and hindgut. These are called
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A person with a mutated SRY gene will
a. be an XX female. b. have normal male genitalia. c. be sterile. d. have both male and female genitalia. e. have no genitalia
Consider a strand of DNA with the sequence GAATTCGGCA. What is the sequence of the complementary strand?
A) ACGGCTTAAG B) AGGCCTAATG C) CTTAAGCCGT D) GAATTCGGCA