What is the evolutionary significance of crossing over?
What will be an ideal response?
New genetic combinations can occur, perhaps making some members of a population more fit for their environment. New combinations might make the difference in the survival of a species.
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Threshold potential refers to the membrane potential required to:
A. open voltage-gated potassium channels. B. initiate an action potential. C. open voltage-gated sodium channels. D. initiate an action potential AND open voltage-gated sodium channels.
The formation of the bivalent during meiosis
A. is required for the pairing of homologous chromosomes. B. contributes to the genetic diversity of a species. C. ensures that the resulting haploid cells will have the same combination of homologous chromosomes as the original diploid cell. D. aids the alignment of sister chromatids in a single row along the metaphase plate. E. occurs during meiosis II.
The cells that normally lack a nucleus and have a relatively short life span in humans are
A. eosinophils. B. lymphocytes. C. neutrophils. D. erythrocytes. E. basophils.
Repressor proteins do not
a. prevent binding of RNA polymerase to DNA. b. cause the DNA regions that contain the operator to twist or loop. c. inactivate operon genes when their products are not required. d. bind to sets of operators. e. increase transcription rates