Chapter 26 practice problems / quiz problems / HIV problems Flashcards
If organisms A, B, and C belong to the same class but to different orders and if organisms C, D, and E belong to the same order but to different families, which of the following pairs of organisms would be expected to show the greatest degree of structural homology?
A. A and D
B. B and D
C. B and C
D. D and E
D
Your professor wants you to construct a phylogenetic tree of orchids. They give you tissue from seven orchid species and one lily. What is the most likely reason they gave you the lily?
Question 6 options:
A. to see if the lily and the orchids show all the same shared derived characters
B. to demonstrate likely homoplasies
C. to see if the lily is a cryptic orchid species
D. to serve as an outgroup
D
The lakes of northern Minnesota are home to many similar species of damselflies of the genus Enallagma. These species have apparently undergone speciation from ancestral stock since the last glacial retreat about 10 thousand years ago. Sequencing which of the following would probably be most useful in sorting out evolutionary relationships among these closely related species?
A. mitochondrial DNA
B. conserved regions of nuclear DNA
C, amino acids in proteins
D, ribosomal RNA
A
Which levels of the classification do humans and leopards share? Refer to figure 26.3
Humans are classified in the same Domain, Kingdom, Phylum, and Class as leopards. They do not share a similar order, as leopards are part of the order Carnivore, and humans are not.
Decide whether each of the following pairs of structures more likely represents analogy or homology, and explain your reasoning. (a) a porcupine’s quills and a cactus’s spines. (b) a cat’s paw and a human’s hand; (c) an owl’s wing and a hornet’s wing.
A: analogy, given that porcupines and cacti are more than likely not closely related and therefore developed these structures despite ancestry
b. Homology: these two organisms are more closely linked
C. Analogy, owls and hornets are not closely linked and the structure of the wings are also different
Suppose that two species, A and B, have similar appearances but very divergent gene sequences, while species B and C have very different appearances but similar gene sequences. Which pair of species is more likely to be closely related: A and B or B and C? Explain
B and C are more than likely closely related. Small genetic changes can have astronomical effects on morphology expression (ex. hox genes) but if genetic sequences have diverged between two organisms, it’s more than likely that these two organisms are not closely linked
Draw a phylogenetic tree that includes the relationships from figures 25.7 and figure 26.16. Traditionally, all the taxa shown besides birds and mammals were classified as reptiles. Would a cladistics approach support that classification? Explain.
The tree that is drawn shows that the traditional classification is a poor representation of actual evolutionary descent. The classification process via cladistics should indicate evolutionary descent as the only means of classification.
According to the tree, both mammals and birds share a reptilian ancestor. Birds are more closely related to dinosaurs than they are mammals, and thus classifying all taxa besides birds and mammals as dinosaurs is a misclassification
Explain how comparing proteins of two species can yield data about the species’ evolutionary
relationship.
Proteins are a genetic byproduct. They are a result of encoding genetic sequences that are expressed in certain ways to yield a protein product. Thus, proteins can be used to classify species as similar proteins = similar genetic sequences.
To distinguish a particular clade of mammals within the larger clade that corresponds to class Mammalia, would hair be a useful character? Why or why not?
No, distinguishing a clade of mammals from a larger clade of mammals and using hair would not be a useful character, as it would be a shared ancestral character among all mammals. Derived traits between mammalian species would be a much better indication of genetic closeness.
The most parsimonious tree of evolutionary relationships can be inaccurate. How can this occur?
The practice of finding the most parsimonious tree is finding the simplest explanation of the evolutionary relationship that is consistent with fact. This can be problematic though, since the evolutionary process is more complicated at times, and this approach does not consider convergent evolution either
Suppose gene A is orthologous in species 1 and species 2, and gene B is paralogous to gene A in
species 1. Suggest a sequence of two evolutionary events that could result in the following: Gene A
differs considerably between species, yet gene A and gene B show little divergence from one
another?
Gene A (orthologous between species 1 and 2 but genetically very different) diverged between the two species much earlier (hence the genetic variation between the two) than when Gene B duplicated from Gene A (hence the little genetic variation between the two).
Review figure 18.13, then suggest how a particular gene could have different functions in different
tissues within an organism.
Genes can be present in an organism but not expressed in certain areas because of transcription factors that regulate when a specific gene sequence should be expressed or not. This allows for particular mRNA molecules to be constructed that fit the necessary protein needs for that particular region of tissues.
What is a molecular clock? What assumption underlies the use of a molecular clock?
The molecular clock allows researchers to date evolutionary lineages and changes in a species by assuming that some genetic information changes at a constant rate (orthologous genes that are inherited by multiple species)
Explain how numerous base changes could occur in an organism’s DNA yet have no effect on its fitness.
Genetic sequences can change and have little effect on an organism’s phenotypic morphology. Since phenotypic characteristics more often determine fitness, changes in genetic sequences that do not cause major morphological changes will then (most likely) have no effect on the organism’s fitness.
Suppose a molecular clock dates the divergence of two taxa at 80 million years ago, but new fossil evidence shows that the taxa diverged at least 120 million years ago. Explain how this could
happen.
The assumption of a genetic sequence that changes at a predictable and clock-like rate was not accurate, as the genetic sequence seemed to change at lower speeds than anticipated (hence the underestimation of the age of the divergence).
