Chapter 15 Quiz

. Which observation is inconsistent with Haeckel's idea that "ontogeny recapitulates phylogeny"?

The backbone—the common structure among all vertebrates such as fish, reptiles, and mammals—appears as one of the earliest structures in all vertebrate embryos.

Snakes and legless lizards develop "leg buds" as embryos, only to have them reabsorbed prior to hatching.

All tetrapod embryos display pharyngeal clefts, a notochord, segmentation, and paddlelike limb buds.

The pharyngeal clefts and branchial arches of embryonic mammals and reptiles never acquire the form seen in adult fish.

In reptile embryos, two bones develop into the articular bones of the hinge of the jaw, while these same bones become the hammer and anvil of the inner ear in marsupials.

. Some salamander species retain gills and other larval characteristics throughout adult life. This is an example of

heterozygosity.

allometry.

neoteny.

canalization.

phenotypic integration.

. A famous example of allometry, the antlers of the extinct Irish elk (Megaceros giganteus)

were expressed at a different position from those of any other deer.

were expressed at a different time during ontogeny from those of any other deer.

grew at the same rate as the deer's body mass.

were larger, relative to body mass, than those of any other deer.

were smaller, relative to body mass, than those of any other deer.

. Which of these would be considered a cis-regulatory element for a gene?

A region of DNA sequence upstream of a gene where transcription factors bind

A protein that binds to an enhancer to activate gene expression

A ribosome that translates a mRNA sequence to produce a transcription factor

Methylation of DNA preventing transcription

A DNA binding protein that functions to repress transcription

. You perform an in situ hybridization on Drosophila melanogaster embryos. You apply a probe labeled with a fluorescent stain that is complementary to mRNA transcripts of the gene hunchback. In early stages of embryogenesis you observe fluorescence for the entire anterior half of the embryo only. In embryos at a later stage of development you see the same pattern in the anterior, and also a stripe of fluorescence in the posterior half. What can you conclude about the expression of hunchback from this?

Hunchback expression is more important in the anterior than in the posterior.

Hunchback has been "knocked out" in some portions of the embryo.

Hunchback is never expressed in the posterior half of the embryo.

Hunchback is first expressed in the anterior of the embryo and later in a portion of the posterior.

Hunchback moves from the anterior of the embryo to the posterior during development.

. The Ultrabithorax mutation changes the halteres (balancing organs) of Drosophila melanogaster into wings by modification of the third thoracic segment into a repeat of the second. What other morphological effects might you expect to see in flies carrying this mutation?

Antennae are replaced with small versions of the legs.

The third pair of legs more closely resemble the second pair than they do in nonmutant flies.

The first pair of wings are replaced with halters.

The third thoracic segment has ectopic eyes.

The position of the first thoracic segment has been changed.

. Refer to the figure showing eyes that were induced to develop in abnormal places in fruit flies (Drosophila melanogaster) by inserting extra copies of either the fly eyeless gene (A, mouthparts) or the corresponding mouse gene, Pax6 (B, leg region).

Human eyes have a very different morphology from that of fly eyes. If Pax6 sequence and function is highly conserved, how can one explain morphological divergence in eyes and their ectopic expression in these flies?

Pax6 and eyeless genes arose independently, but have similar function.

Both genes turn on eye development, but different genes are regulated by them in different species.

Humans and fruit flies share a common ancestor much more recently than previously thought.

Pax6 does not suppress eye development as well as eyeless.

Pax6 and eyeless must not be part of the developmental pathway.

. Imagine a scenario in which several lakes have been colonized by marine-origin sticklebacks. In each lake, body armor disappears over time. Which change most likely caused this?

Independent, unique mutations occurred in each population that rendered enhancers in the armor pathway useless, which were then favored by natural selection.

Each population had the exact same mutation in a protein coding gene that produces the armor, which increased in frequency by natural selection.

Novel trans-regulatory elements functioned to build new, armorless morphologies that increased in frequency because of gene flow from oceanic populations.

Alternative splicing allows the fish to produce the level of armor appropriate for the environment.

Lack of armor reduces fitness, so only genetic drift could cause the armorless condition to increase in frequency.

. Why do the same trans-regulatory elements lead to very different morphology in different species of organisms?

These regulatory elements have no effect on morphology, only metabolism.

Different species have genetic codes that use different codons, leading to different amino acid sequences.

The transcription factor activates different combinations of enhancers and downstream genes.

The trans-regulatory elements in different lineages have independently evolved the same sequence, by convergent evolution.

Morphological change depends on sequence mutations in enhancers.

. In which example are the proximate cause and the ultimate cause of morphological evolution correctly matched?

Proximate: cis-regulatory elements are found upstream of a gene; ultimate: cis-regulation is required to activate a gene

Proximate: changes in gene regulation lead to changes in morphology; ultimate: natural selection favors morphologies that work best in their environment

Proximate: point mutations in protein coding genes affect protein function and structure; ultimate: chemical and physical configuration of a protein affect its function

Proximate: natural selection favors gene combinations that have high fitness in their environment; ultimate: genetic changes alter morphology and fitness

Proximate: natural selection causes morphology to differ among species; ultimate: natural selection prevents morphological variation within a species

. Which would place the greatest constraint on evolvability in a population experiencing directional selection?

High magnitude of additive genetic variance

Genetic correlation of functionally related traits that allow new and better combination of character states

Phenotypic integration of interacting structures

High heritability of features used together

Lack of co-variation in structures that depend on close match to each other

. What was necessary for human hands and feet to become specialized for functions very different from each other, compared to apes and other primates?

Decoupling the pleiotropic genes that pattern the hands and feet

An alteration in anterior-posterior patterning by changes in Hox expression

Duplications of Hox genes to allow for more specialized body plans

An increase in pleiotropy of the genes responsible for limb development

Phenotypic integration of the digits of the hands and feet

. Evolution can be constrained by several factors. Which of the following describes a developmental constraint?

Limitations set by the genome and genetic variation of the most recent common ancestor

Properties of biological material that prevent certain morphologies from being possible

A bias in the production of phenotypes caused by the structure, character, or composition of how an organism is built

A constraint preventing a trait from evolving because the trait is always disadvantageous

A constraint preventing certain evolutionary trajectories because genetic variation enabling those trajectories is absent

. What is a "reaction norm?"

The complete set of interacting genes necessary to produce a developmental module

When the effect of environmental differences on the phenotype differs from one genotype to another in a population

The ability to produce the same structures and morphology, regardless of environmental differences

A character that originally developed in response to the environment that has become genetically determined

The complete range of phenotypes that an organism can produce in different environments

. Closely related species pairs in which the reaction norm of one species includes a phenotype that is invariant in the other species is used by Mary Jane West-Eberhard as evidence for

phenotypic plasticity.

genetic accommodation.

canalization of traits.

genetic assimilation.

phenotypic integration.

Chapter 15 Quiz

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