Genetic Evidence suggests that feathers evolved . . .单项选择题

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The TAS2R38 gene encodes a receptor protein that influences the ability to taste bitterness. The gene has two alleles: a dominant, wild-type allele that enables an individual (taster) to taste bitterness and a recessive, mutant allele that interferes with the ability of an individual (nontaster) to taste bitterness. Three single nucleotide mutations in the coding region of the TAS2R38 gene are associated with the nontaster allele. The nucleotides present at the three positions are shown in the table below. Nucleotide Variation in the TAS2R38 Gene Position in the Nucleotide Sequence 145 785 886 Human nontaster G T A Human taster C C G Bonobo C C G Chimpanzee C C G Gorilla C C G A cladogram representing the evolutionary relatedness of selected primates is shown below. From left to right, the branches are as follows: Orangutan, Gorilla, and Chimpanzee. Past the branches, the main line is labeled Human. Another branch, labeled Bonobo, is connected to the Chimpanzee branch. Toxic substances often have a bitter taste that causes animals who try to eat such substances to spit them out rather than swallow them. Additional data suggest that gorilla populations have a very low frequency of nontasters. Which of the following scientific questions will best help researchers determine when the nontaster allele arose in the evolutionary history of the selected primates?

The loss of pelvic spines in freshwater populations of stickleback is due to?

Spots of pigmentation are a characteristic that varies considerably in different species of Drosophila.  In the Figure provided below there is a phylogenetic tree that includes information on species that have spots (indicated by the black circle) and those that lack the spot (indicated by the open circle).  The percentages at the nodes representing hypothetical common ancestors in these lineages is the probability that the indicated ancestor had wing spots.    From the following species, identify those that are appropriate to study the underlying molecular basis for the loss of the wing spot characteristic.     

Spots of pigmentation are a characteristic that varies considerably in different species of Drosophila.  In the Figure provided below there is a phylogenetic tree that includes information on species that have spots (indicated by the black circle) and those that lack the spot (indicated by the open circle).  The percentages at the nodes representing hypothetical common ancestors in these lineages is the probability that the indicated ancestor had wing spots.    From the following species, identify those that are appropriate to study the underlying molecular basis for the gain of the wing spot characteristic.    

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