Mtl, polA, and xyl are bacterial genes that can be transmitted using an Hfr strain. An interrupted mating experiment resulted in xyl exconjugants appearing at 7 minutes and reaching maximum level by 30 minutes
The mtl gene function exconjugants appeared at 11 minutes and leveled off at 80% maximum by about 33 minutes, while polA did not appear until 24 minutes into the experiment and then only slowly rose to about 30%. Which of the following shows the gene order with the insertion site (arrow) location correctly? A) xyl mtl polA ?
B) polA mtl xyl ?
C) mtl xyl polA ?
D) mtl polA xyl ?
E) None of these
B
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The oldest cells in a mature leaf are found ____
a. at the base of the leaf b. near the very center of the leaf c. at the stomata d. at the leaf tip e. as files of cells at the widest point of the leaf
A form of mutation associated with the expansion in copy number of a nucleotide triplet in or near a gene is called
a(n) ____________________ Fill in the blank(s) with the appropriate word(s).
Which of these is a difference between a DNA and an RNA molecule?
a. DNA contains uracil, whereas RNA contains thymine. b. DNA is double-stranded, whereas RNA is single-stranded. c. DNA contains five-carbon sugars, whereas RNA contains six-carbon sugars. d. DNA contains nitrogenous bases, whereas RNA contains phosphate groups. e. DNA is a polymer composed of nucleotides, whereas RNA is a polymer composed of nucleic acids.
How is it that the cells in different body tissues are able to perform different functions?
A) The cells exhibit different patterns of gene expression. B) Different chromosomes have been inactivated in different cells. C) The cells contain different genes. D) The mutations that have accumulated in the cells of the different tissues control functions.