Why is the traditionally defined taxon Reptilia paraphyletic?
What will be an ideal response?
ANSWER: A paraphyletic taxon includes an ancestral species and only some of its descendents.
Amphibian and mammalian lineages each diverged early from an ancestral tetrapod, while
the remaining lineages, collectively called Reptilia, diverged into the Lepidosauromorpha
(including living lizards and snakes) and the Archelosauromorpha (including living turtles,
crocodilians, and birds). Thus, although crocodilians, with their scaly skin and sprawling
posture outwardly resemble lizards, evolutionary biologists have long recognized that
crocodilians share a more recent common with birds. However, the traditionally defined
taxon Reptilia is clearly paraphyletic because, even though crocodilians share a common
ancestor with birds, Reptilia includes the former taxon, but not the latter. Thus, birds share
a common ancestor with reptiles, but birds are placed in a separate taxon.
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In humans and some primates, the most abundant neurons are the ____
a. efferent neurons b. afferent neurons c. interneurons d. motor neurons
e. sensory neuronsExplain how a hormone will trigger the signal transduction pathway in a plant.
What will be an ideal response?
Which of the following requires treatment with both antibiotics and antitoxins?
A) diphtheria B) tuberculosis C) whooping cough D) scarlet fever E) psittacosis
Pax6 is a transcription factor noted for its unique role in specifying eye development across the animal kingdom. A homologous gene known as eyeless specifies eyes in Drosophila, and misexpression of mouse Pax6 can cause ectopic eyes in flies! This creates a quandary - how can we explain the universality of the master regulatory gene for eye development, with the striking variability of eye anatomy in different phyla?Misexpression of the Pax6 gene was shown to promote eye development in both vertebrates and invertebrates. The authors of this study suggested that this was evidence that eyes evolved only once. What other evidence contradicts this view?
A. Invertebrates normally have only simple eyespots. B. The anatomical structure of insect, mollusk, and vertebrate eyes are quite different. C. Many different transcription factors can initiate eye development when misexpressed. D. While the anatomy of all animal eyes is the same, lens proteins vary greatly.