In Drosophila, mutation screening usually involves use of a balancer chromosome that includes three elements: a set of overlapping inversions, an easily recognized dominant mutation, and a recessive lethal mutation that prevents balancer homozygotes
from surviving. Which one, or combination, of these elements is necessary and sufficient to suppress crossovers? A) inversions
B) dominants
C) lethal recessive
D) inversions plus dominant
E) lethal plus inversions
A
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Which of the following statements about crossing over is false?
A. Crossing over takes place between non-sister chromatids. B. Crossing over takes place between sister chromatids. C. Crossing over occurs during prophase I. D. Sites of crossing over are called chiasmata. E. Crossing over is also called genetic recombination.
The portion of the flower containing pollen grains is
(a) the pollen sac. (b) the microsporangium. (c) the anther. (d) all of the above.
The mitochondrial genome consists of ________ genes.
A) 12 B) 37 C) 250 D) 370
Which one of the following does not match a component of the amniotic egg with its primary function?
A. Shell-porous, protective covering B. Yolk sac-provides food for the embryo C. Allantois-segregates nitrogenous wastes from embryo D. Chorion-exchange of respiratory gases; retention of water E. Amnion-encloses embryo within an oxygen-filled cavity