Homework 5: Ch. 26 Phylogeny

Can you match these prefixes, suffixes, and word roots with their definitions?

disease: path- false: pseudo- out of: ex- mouth: stoma alongside: para- head: cephal- second: deutero- backward: retro-

Imagine that you are studying alien life-forms discovered on a distant planet. While geneticists are working out the genetic code of these organisms, you are asked to construct a phylogenetic tree based on four morphological features, or characters: presence or absence of a spring tail, presence or absence of a grasping hand, presence or absence of a second tail, and number of eyes. The organisms have been divided into five groups based on these characters. If we assume the alien with a tail stalk is an outgroup, what is the most likely phylogenetic tree based on these shared derived characters? When did these characters appear during the aliens' evolutionary history?

*The presence or absence of characters can be used to build a phylogenetic tree based on morphology. In this example, all aliens other than the outgroup have a spring tail, all but two of the groups have a fourth eye, two of the aliens have two tails, and one of the aliens has a grasping hand. These characters can be used to create a hypothesis about the evolutionary relationships between these organisms.*

Suppose that a phylogenetic tree were constructed using the data shown in this table. Mosses represent the outgroup. What would the resulting tree suggest?

Cherries and peas are each other's closest relatives *Cherries and peas both have flowers and fruits. In fact, they share all the characters listed in the table. That is, they both have vascular systems, seeds, and flowers and fruits, and they both lack cones.*

This is one possible phylogenetic tree representing the relationships between some members of phylum Arthropoda. Use this phylogenetic tree and your knowledge of cladistics to determine the relationships between these species. Rank the species from most closely related to horseflies to most distantly related to horseflies. If two species are equally close in their relatedness to horseflies, overlap them.

Most CLOSELY related to horseflies 1: flea 2: katydid, human body louse 3: dragonfly, mayfly 4: silverfish Most DISTANTLY related to horseflies *Phylogenetic trees show the evolutionary relationships between organisms. Closely related organisms have more common ancestors than distantly related organisms. In this case, fleas are more closely related to horseflies than are any other species on the tree, even though some of the other species look more like horseflies than fleas do.*

Based on the character table in Part B, which of the following statements about shared derived characters in plants is correct?

Seeds are a shared derived character of pines, cherries, and peas. *Seeds are a derived character of pines, cherries, and peas. We can also see that: the vascular system is a derived character of ferns, pines, cherries, and peas; flowers and fruits are a derived character of cherries and peas; and cones are a derived character of pines.*

Look at this character table. Rattlesnakes (like turtles) are reptiles, yet they do not have four limbs. In fact, they have no apparent limbs. What does this suggest?

The presence or absence of four limbs, on its own, could be misleading when considering the evolutionary relationships of rattlesnakes. *The loss of limbs in snakes is an example of a situation where, over the course of evolution, a subgroup of a lineage loses a character that is typically found in other members of that lineage. Snakes evolved from a reptilian ancestor that had four limbs, but over time, these limbs became highly reduced or lost in the snake lineage. The "four limbs" character could be misleading because, on its own, it might suggest a relationship between rattlesnakes and other species that do not have four limbs, such as the lamprey and bass. However, many other traits of rattlesnakes (such as the amnion) show their kinship with other reptiles.*

Can you match these prefixes, suffixes, and word roots with their definitions?

cartilage: chondr- blood: hem- (or hemato-) skull: crani- shape, form: morph- eat: phago- hollow: coel- change, after: meta-

Which of the following would, if it had acted upon a gene, prevent this gene from acting as a reliable molecular clock?

natural selection

The geneticists studying the alien organisms have deciphered their genetic code. For familiarity, they have used A, C, G, and T to indicate the bases in this code. A comparable genetic sequence in each alien has been identified in the genes that code for eye growth. This genetic sequence has allowed the aliens to be divided into six groups, with the single-tail, three-eye group split in half. The geneticists also studied several outgroup species (not shown) to compile a likely ancestral DNA sequence. From this information, they have constructed four possible phylogenetic trees. Based on this genetic information, which phylogenetic tree is most parsimonious?

phylogenetic tree III *Tree III requires the fewest base-change events, so it is the most parsimonious phylogenetic tree. Based on this genetic evidence, we can hypothesize that group 2b diverged from group 2a at the same time that groups 3, 4, and 5 diverged from group 2a. Either the addition of a fourth eye came after this divergence, or group 2b lost its fourth eye sometime in this group's evolutionary history.*

Can you match these prefixes, suffixes, and word roots with their definitions?

seed: sperm inside, inner: endo- egg: oo- (or ov-) outside: ecto- skin: derm life: bio- plant: -phyte middle: meso-