Watson and Crick developed a model of DNA in which the two strands twist into the shape of a ________.
A. double helix
B. circle
C. double pleated sheet
D. helix
Answer: A
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What is the difference between a forward and reverse mutation?
A. A forward mutation is beneficial to the organism, while a reverse mutation is harmful to the organism. B. A forward mutation changes the genotype to the wild-type genotype, while a reverse mutation changes the genotype to a mutant genotype. C. A forward mutation changes the wild-type genotype to some new genetic combination, while a reverse mutation changes a genotype to the wild-type genotype D. None of the answers are correct
Diatoms have a special problem:
A. because their + and - mating strains are nonmotile and have to be dispersed by currents B. because their heavy siliceous shells impede conjugation C. because they must await a chemical signal from a fish before they can become mobile and search for mating partners D. because their two halves fit like the lid and body of a pillbox and on repeated cell divisions the half that is overlapped gets progressively smaller E. because the gametes experience difficulty in exiting the overlapping halves of their siliceous shells
If speciation occurs with the production of two or more species in a small area, ____ is (are) probably
responsible.
a. both sympatric and parapatric speciation b. either sympatric or parapatric speciation c. neither sympatric or parapatric speciation d. only sympatric speciation e. only parapatric speciation
A hydrogen atom consists of
What will be an ideal response?