INSTRUCTIONS
1. Write your NAME on EVERY PAGE
2 Use the number of points and suggested times to allocate your time and effort appropriately.
3. ANSWER ONLY IN THE SPACE PROVIDED! If you need a lot more space you probably are not answering the right question.
4. Be CONCISE. Use GRAPHS, TABLES, LISTS or other aids wherever possible, and always LABEL them fully. Wherever possible, refer to (but don't explain in detail) appropriate EXAMPLES.
I. DEFINITIONS
Define each term clearly, concisely and completely. Give an example for each term.
(5 points per question ; approximately 2-3 minutes per question)
The Hadley Cell is the name given to the two convection cells (1 north of the equator and the other south) that exists between the equator and 30 degrees latitude. It is formed by the convective rising of warmed air at the equator, and the subsequent spreading of that air (noth and south) as it rises and continues to warm. It then cools and the air begins to sink (at 30 degrees). After sinking the air moves along the surface of the earth back towards the equator to fill the low pressure area at the equator created by the rising air. This surface air movements, interacting with the coriolis effect, drive the global wind patterns between 0 and 30 degrees latitude.
2. Cyanobacteria
The earliest photosynthetic organism. This prokaryote converted CO2 to O2 thus changing the earth's reducing atmosphere to an oxidizing atmosphere.
3. Neutral Mutation
A mutation that has no selective consequences. For example, mutations at the third codon are often silent (no change in amino acid composition of a protein) because of the redundancy of the genetic code. Other truly neutral mutations include non-coding DNA or mutations in psuedogenes. Other mutations are nearly neutral or quite selective.
An assumption regarding the constancy of mutation rate over evolutionary time that allows us to compute a time scale that is based number of mutations between two branches in an evolutionary tree. A molecular clock is usually calibrated using information from the fossil record. For example, mutations in neutral areas of mitochondrial DNA are used to compute a molecular clock for the "mitochondrial eve". Studies targeting neutral DNA should theoretically yield more accurate computations.
5. Parsimony
Parsimony is the evolutionary principle that evolution proceeds slowly (or that traits are conserved). If parsimony is the true state of the world, then phylogenetic reconstruction that minimizes the number of evolutionary changes is considered a better tree compared to less parsimonious trees that have more evolutionary changes. Many possible examples could be used.
II. DISTINCTIONS
Show clearly but concisely that you understand the essential differences between the two terms in each question. Give an example for each that reinforces your explanation.
(5 points per question; approximately 2-3 minutes per question)
1. Tundra vs. Taiga
Tundra is the treeless polar biome found in places such as the Alaskan N. slope, or in the Sierra alpine. Tundra is cold, of moderate moisture, and may or may not have permafrost (polar tundra does have permafrost, whereas alpine tundra usually does not). Taiga is the temperate, wet biome characterized by coniferous forests. An example of taiga would be the redwood forest found right here in Santa Cruz.
2. Environmental "buffering" vs. environmental "modification"
Environmental "buffering" is the reduction of variation or extremes in environmental conditions about a mean. For example, bodies of water or forests may reduce ambient temperature within a certain range in that particular environment. Environmental "modification" is when organisms actually change environmental conditions (altering the mean). An example of modification is beavers modifying aquatic habitats through the construction of dams.
3. Natural and sexual selection
Natural selection arising from differential or survival of heritable variation that generally leads to increased adaptation ("fit between an organisms and the environment") or an increase in the average fitness of a population. Sexual selection is differential acquisition of mates owing to for example, an attractive ornament (or potent armament). An example of natural slection can be the evolution of thicker fur in mammals as a result of a colder climate change, where those individuals who acquired a mutation for longer fur ended up having greater reproductive success (due to increased survival), thereby passing on the trait for longer fur to future generations. The evolutionary elaboration of such sexually-selected traits does not necessarily lead to higher population fitness because many males might die owing to the costly ornaments. Sexual can result in a certain degree of maladaptation. Examples of sexual selection are swords on swordtail fish (female preference for swords increase reproductive success for males with certain length of swords), or antlers on moose (male-male competition).
4. Allopatric and Sympatric speciation
Allopatric speciation takes place in different geographic regions whereas sympatric speciation takes place in the same geographic region. (e.g., ring species is a special from of allopatric speciation by great distance [where the ends of the ring meet] versus speciation in insects and host plants which arise on adjacent species of fruit trees [apple versus cherry] ).
5. Cephalization and Tagmatization
Cephalization results in the elaboration of head structures by the successive incorporation of trunk segments (e.g., antenna versus mandible). Tagmatization is the sequestering of trunk segments in regions of the body with specialized function (e.g., feeding structures in the head versus locomotor structures in the trunk versus reproductive structures in the abdomen).
III. SHORT ANSWERS
Use short essays, labeled diagrams or lists for complete but concise answers.
(10 points per question; approximately 10 minutes per question)
1. What is "climate"? What is(are) the essential difference(s) between "climate" and "weather"?
(5 pts.) Climate and weather are the prevailing regimes of temperature and water or the net effects of gain, storage, transport, loss of heat and water. The difference between climate and weather is one of scale: climate measures these effects on a large (regional-global) and long (years to centuries) scale, whereas weather measures these effects on a small (local-regional) and short (hours-days) scale.
This map shows some features of climate and some of weather. Indicate and label the most important expressions of each, and use these symbols to classify each: (C) = climate; (W) = weather. the positions of major convection cells and the convergences between them; regions of high (H) and (L) pressure; and the directions of prevailing surface winds.
1 point each for labeling the following: features of climate (H and L pressure systems, convection cells); feautures of weather (rain, snow, fronts); the positions of major convection cells and convergences; regions of high and low pressure (including and surrounding convergent zones); the directions of prevailing surface winds (according to the location and the direction of the convection cells on the surface of the earth, and the result of the Coriolis effect). If you did not relate these features directly to the weather map, one half of a point was marked off.
2. Outline the major interactions linking (a) the origin and early evolution of life with (b) the development of today's global environment. Explain why new life forms are unlikely to arise spontaneously on the modern Earth, and are unlikely to become established if they did.
There are two reasons for which new organisms are unlikely to spontaneously arise on earth today. Firstly the conditions of the early earth in which the first forms of life arose no longer exist on the planet today (2 points). There are five conditions which favored life in the early earth: moderate temperatures, liquid water, solar or chemical energy, small organic molecules, and small soluble minerals. Furthermore the earth had a CO2 atmosphere (a reducing atmosphere) which favored reactions that joined small organic molecules into larger complexes (leading to life!!) (3 points). With the rise of plants, and thus photosynthesis, the atmosphere changed from a reducing to an oxidizing atmosphere through the addition of oxygen. This new atmosphere no longer favors reactions between small organic molecules (3 points). The second reason that new spontaneous life does arise on today's earth is that through years of evolution most (if not all) niches are filled. New spontaneous life is unlikely to be competative enough to take over these niches in the face of the specialists that currently occupy them (2 points).
3. You have found in two separate valleys along the Sierra mountains two small, distinct populations of the same lizard. One population is parthenogenic (asexual) while the other is sexual. You decide to mark the populations' progress in time. How do you expect the populations to fluctuate in the short term? the long term? Why do you expect these patterns?
In the short-term the asexual population should increase much more rapidly than the sexual population because of the two-fold advantage of asexuals. Asexuals only produce daughters whereas sexuals waste gross reproductive output by producing sons (2 points). However in the long-term, the asexual population should begin to decline relative to the sexual lineage, which continues to grow at the same rate, (2 points) owing to two potential benefits of sexual reproduction. Sexual reproduction allows the lineage to escape the effects of Muller's ratchet or the accumulation of deleterious recessives through recombination of genes (2 points). However, the asexual lineage cannot purge their genome (they are clones) and mutations accumulate slowly over time which tends to lower the two-fold fitness advantage of asexuals (2 points). A second problem faced by the asexual lineage is the presence of parasites that might eventually lock onto the genotype of asexuals and cause their population to decline (Rice's ratchet) (2 points). In contrast, the sexual lineages produce new genotype combinations by segregation and recombination and thereby keep ahead of the parasites and develop new resistance genes.
4. What are the five microevolutionary assumptions underlying the Hardy-Weinberg Theorem (define each very briefly)? What are two key predictions of the H-W theorem?
No selection -- the selective elimination or reproduction of genotypes.
No migration -- gene flow or the movement of genes across geographic regions.
No mutation --- the production of novel genotypes by spontaneous and random mistakes of replication.
No gene drift (or infinite population size) -- genetic drift arise from the sampling effects of limited population size which allows for stochastic changes in gene frequency with time.
Mating is random -- genotypes do not mate assortatively or disassortatively but rather the fusion of one gamete regardless of genotype is independent of the genotype of the second gamete.
Predictions:
Gene frequency does not change from generation to generation.
The genotype frequencies will be found in the ratio: p2, 2pq, q2.
5. a) What selective events are thought to be behind the Cambrian explosion?
b) What development mechanisms are likely to have contributed to the explosion of body plans seen during the Cambrian (discuss the processes of tagmatization and cephalization, and their developmental regulation)?
a) The major selective events that are thought to be behind the cambrian explosion is the rapid filling of vacant niches that were essentially empty owing to a "wide open" adaptive landscape (Anology: much like settlers in the western USA before the turn of the 19th century). The filling of some of these niches (e.g., herbivore niches) led to the creation of yet more new niches (e.g., predatory niches) further fueling the rapid explosion of morphological diversity (Analogy: miners in the west fuel the economic growth of the mercantile business).
b) The key developmental mechanisms would be the duplication of an existing gene that controls development of one segments (e.g., in the head). Because the gene is duplicated, the original gene keeps normal developmental control of the original segment and the gene duplication mutation is selectively neutral as it controls no other gene. However, another mutation might occur that allows this as yet "pseudogene" to be used to alter or take over the developmental regulation of a more posterior segment. The new segment can be then selected for further advantageous mutations that cause it to be modified for a new function (e.g., accessory feeding structure). A a larger scale, the body plans would also be modified by the process of tagmatization in which blocks of genes controlling head development might be duplicated on mass. The new block of genes might under further mutations that allow it to take control of a new large block of posterior segments (e.g., thorax) that allows for new functions to evolve (e.g., development of novel locomotor structures in thorax or reproductive structures -- typically in the abdomen).
[Alternative answer for development: One could also describe how new genes shut down the original developmental fate of a structure such as the double pair of wings in insects to create a novel dipteran, while an accurate depiction of how genes for development mutate and evolve, the evolution of insects really occurred 100's of millions of years later in the Devonian. However, the same kind of mechanism might have occurred in the Cambrian Explosion creatures.]