What character state distinguishes Cnidarians from Bilaterians in the phylogenetic tree in Figure 35.2?
A. presence or absence of ganglia
B. presence or absence of sensory neurons
C. presence or absence of interneurons
D. presence or absence of motor neurons
A
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It has since been discovered that many plants synthesize molecules that destroy the corpora alata, the structures responsible for synthesis of juvenile hormone. How do levels of juvenile hormone disrupt the insect life cycle?
A. Exposure to juvenile hormone prevents the larvae from developing into adult insects. B. Exposure to juvenile hormone causes juvenile insects to die. C. Excess juvenile hormone causes insects to molt prematurely. D. Exposure to juvenile hormone prevents molting.
How can a single gene code for more than one protein?
A) Different types of ribosomes translate the resulting mRNA, producing different proteins. B) The exons within an mRNA can be spliced together in different ways. C) Different amino acid chains can be coded by the same mRNA. D) Different RNA polymerases transcribe it and produce different proteins.
Diffusion
What will be an ideal response?
A researcher is interested to test the hypothesis that a 100 base pair stretch of a given gene is under selection
She sequences this gene region in 30 individuals, each of two populations. She finds that within either popula-tion, there are 33 synonymous sites of which 10 are segregating for different alleles in the population. In this same sequence, she observes 29 sites within-populations that possess variable alleles at nonsynonymous sites. In contrast, when she compares substitutions across species, she finds that of the 33 synonymous sites only five show signs of a substitution between species. Only 15 nonsynonymous substitutions were observed between species. This suggests that the gene is: a. under purifying selection. b. under nearly neutral selection. c. under positive selection. d. under directional selection. e. This cannot be determined based on the information provided.