Bio Test 2
Describe the evidence that suggests that RNA was the first genetic material. Explain the significance of the discovery of ribozymes
RNA is central to information transfer in a cell. RNA can be copied abiotically, Ribozymes have a variety of catalytic functions; pre-date enzymes
Explain how the evolution of changes in temporal and spatial developmental dynamics can result in evolutionary novelties
Relatively few genes control timing and proportions Small genetic alterations can have big effects Changes in Rate and Timing Heterochrony: evolution of morphology from modifying relative growth rates in different parts Paedomorphosis: retention of juvenile characteristics in the adult due Changes in Spatial Pattern May involve changes in the expression of homeotic genes in animals
Discuss, with a suitable example, how continental drift explains the current or former distribution of organisms
Same Permian freshwater reptiles discovered in both Brazil and West Ghana (they were connected in the past)
Describe the evidence that suggests that mitochondria were acquired before plastids in eukaryotic evolution
Majority of eukaryotes have mitochondria even if they have a plastid so that means that after endosymbiosis of mitochondria, some eukaryotes acquried an additional endosymbiosis of a photosynthetic bacterium (bc some eukaryotes have plastids while all have mitchondria)
Explain why the fossil record provides an incomplete chronicle of evolutionary change
Many of Earth's organisms probably did not die in the right place at the right time to be preserved as fossils. Of those fossils that were formed, many were destroyed by later geologic processes, and only a fraction of the others have been discovered. As a result, the known fossil record is biased in favor of species that existed for a long time, were abundant and widespread in certain kinds of environments, and had hard shells, skeletons, or other parts that facilitated their fossilization
Briefly describe the Cambrian explosion
Many phyla of living animals appear suddenly in fossils formed early in the Cambrian period (535-525 mya), a phenomenon called the Cambrian explosion. Many animal phyla may have originated much earlier, as evidenced by fossils like the 575 million year old ones below. Suggesting that "the Cambrian explosion had a long fuse", as noted by Simon Conway Morris Prior to Cambrian explosion all large animals appeared to be soft-bodied herbivores, but things changed quickly during the Cambrian explosion. Over a period of 10 million years, predator over 1 meter in length emerged with claws and other prey-catching features, and defensive adaptations, like sharp spines and heavy body armor appeared in their prey
Name the reactions that have produced O2 on Earth. Describe the accumulation of atmospheric O2 over time and the effects of this accumulation on living things
1. Photosynthetic bacteria produce O2, which would react with iron forming iron oxide, forming red layers of rock. 2. After iron precipitated out, then water can become saturated with O2, 3. Once saturated then O2 would "gas out" and enter atmosphere about 2.7 bya
Describe the four stages of the hypothesis for the origin of life on Earth by chemical evolution.
1.The abiotic (nonliving) synthesis of small organic molecules, such as amino acids and nucleotides. 2. The joining of these small molecules into macromolecules, including proteins and nucleic acids. 3. The packaging of these molecules into "protobionts", droplets with membranes that maintained an internal chemistry different from that of their surroundings. 4. The origin of self-replicating molecules that eventually made inheritance possible.
Describe how natural selection may have favored the proliferation of stable protobionts with self-replicating, catalytic RNA
A protobiont with self-replicating, catalytic RNA would be different than neighbors without those characteristics. If the protobiont could grow, split and pass on its RNA to its "daughters" its limited inherited characteristics could be acted on by natural selection. Although very rare are those few protobionts, out of the trillions in a body of water, with a limited capacity for inheritance would have had a huge advantage over the rest
Distinguish among directional, disruptive, and stabilizing selection. Give an example of each mode of selection
Directional: galapagos finches when large seeds were most common Disruptive: black-bellied seedcracker finches in Cameroon, 2 diff beak sizes, small for soft seeds, large for hard seeds Stabilizing: Most human babies weigh the same (around 3-4 kg) those w/higher weights have higher mortality rates
Describe the evidence that supports the theory that mitochondria and plastids evolved by serial endosymbiosis. Explain what living organisms are likely relatives of the prokaryotes that gave rise to mitochondria and plastids
Endosymbiosis: englufing other cells -Mitochondria and plastids are descendants of bacteria that were engulfed by other cells and became endosymbionts -mitochondria: all eukaryotes have mitochondria or have had them -plastids: DNA of plastids in red and green algae closely resembles the DNA in cyanobacteria
Describe how natural selection may have worked in an early RNA world
Natural selection on the molecular level has produced ribozymes capable of self application in the laboratory. Unlike the doubled stranded DNA, which takes the form of a uniform helix, single stranded RNA molecules pursue a variety of specific three-dimensional shapes mandated by their nucleotide sequences. In a particular environment, RNA molecules with certain base sequences are more stable and replicate faster and with fewer errors and other sequences. The RNA molecules whose sequence is best suited to the surrounding environment and has greatest ability to replicate self believe the most to send it molecules. Its descendents will not be a single species but instead will be a family of sequences that differ slightly because of copying errors
Explain the function of Hox genes. Describe, with a suitable example, how changes in the number, sequence, or expression of Hox genes can lead to major morphological differences between species
Hox genes determine features such as where a pair of wings and a pair of legs will develop on a bird or how a plants flower parts are arranged. In crusteantions, a change in the location 2 hox genes are expressed correlates with the conversion of a swimming appendage to a feeding appendage
Define evo-devo, heterochrony, and paedomorphosis
evo-devo is research at the interface between evolutionary biology and developmental biology. + heterochrony is an evolutionary change in the rate or timing of developmental events + paedomorphosis is a condition where the rate of reproductive development accelerates compared with somatic development
Explain how quantitative and discrete characters contribute to variation within a population
o Discrete traits - determined by a single locus with different alleles that produce distinct phenotypes; ex: flower color, brown eyes o Quantitative traits - vary along a continuum within a population; ex: plant height in a flower population ranges from short to tall, height, weight o They allow for organisms to have different traits based on allele variation
Distinguish between intrasexual selection and intersexual selection
o Intra: indv compete directly for mates of opposite sex o Inter: indv are choosy in selecting mate from other sex
Define adaptive radiation. Describe, with suitable examples, three circumstances under which adaptive radiation may occur
o Mass extinctions can pave the way for adaptive radiation, in which new groups of organisms rise to prominence. Adaptive radiation occurred in organisms with major innovations such as seeds or armored body coverings or the ability to colonize regions with little competition. Mammals underwent a dramatic adaptive radiation after the extinction of terrestrial dinosaurs 65.5 mya o a period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles or niches + diversification of mammals after the extinction of dinosaurs + evolution of insects to eat or pollinate plants after plants colonized land + "silverwood alliance" plants on the Hawaiian Islands diversified from an ancestral tar weed (allopatric speciation)
Write the Hardy-Weinberg equation. Use the equation to calculate allele frequencies when the frequency of homozygous recessive individuals in a population is 25%
o P^2 + 2pq + q^2 = 1 ????
Describe five prezygotic reproductive barriers and give an example of each
o Temporal In North America, the geographic ranges of the eastern spotted skunk (Spilogale putorius) (c) and the western spotted skunk (Spilogale gracilis) (d) overlap, but S. putorius mates in late winter and S. gracilis mates in late summer. o Mechanical 2 snail species (genus bradybaena) have shells that spin in diff direction and as result snails' genital openings are misaligned o Behavioral east/west meadowlark have different song o Habitat 2 garter snake species (genus Thamnophis) live in same area but one is terrestrial and the other lives in water. o Gametic isolation ea urchins release their sperm and eggs into the surrounding water, where they fuse and form zygotes. It is difficult for gametes of different species, such as the red and purple urchins shown here, to fuse because proteins on the surfaces of the eggs and sperm bind very poorly to each other.
Explain the endosymbiotic theory for the evolution of the eukaryotic cell. Describe the evidence that supports this theory
A range of evidence supports the idea that eukaryotic cells evolved from prokaryotic through endosymbiosis. Endosymbiont = a cell that lives in another cell (host) Endosymbiosis Model = mitochondria and plastids (includes chloroplasts) were formerly small prokaryotes that began living in larger cells. Evidence for Endosymbiosis; organelles share traits with prokaryotes • Inner membranes of both organelles have homologous enzymes & transport systems to those in plasma membranes of prokaryotes • Both organelles replicate by splitting like some prokaryotes • Single circular DNA in organelles & prokaryotes • Organelles have ribosomes and can transcribe & translate their DNA into proteins • Ribosomes in mitochondria & plastids more similar to prokaryotic than eukaryotic cytoplasmic ribosomes
Describe the major events in Earth's history from its origin until 2 billion years ago. In particular, note when Earth first formed, when life first evolved, and what forms of life existed in each eon
From 3.5 billion years ago comes fossilized stromatolites. Stromatolites are layered rocks that form when certain prokaryotes bind thin films of sediment together. It is reasonable to hypothesize that single-celled organisms originated perhaps as early as 3.9 billion years ago if microbial communities complex enough to form stromatolites existed 3.5 billion years ago. Early prokaryotes were Earth's sole inhabitants from 3.5 to 2.1 billion years ago. Photosynthesis and the oxygen revolution left the earth with an oxygenated atmosphere. A few hundred million years later, the rise in O2 accelerated. It is believed that this is because of the evolution of eukaryotic cells containing chloroplasts from about 2.1 billion years ago. Endosymbiosis is a model that explains how eukaryotic features evolved from prokaryotic cells which posits that mitochondria, plastids, and other organelles were formerly small prokaryotes. Serial endosymbiosis supports that mitochondria evolved before plastids through a sequence of endosymbiotic events. Archaen eon-- prokaryotes Proterozoic eon-- first eukaryotic cells, soft-bodied invertebrates & algae Phanerozoic eon: Paleozoic era-- first animals, diverse forests, first tetrapods Mesozoic era-- origin of mammal-like reptiles, dinosaur age, flowering plants Cenozoic era-- mammals, birds, pollinating insects, prime ates, ice age, humans
Define the terms population, and gene pool
Gene pool: all copies of every type of allele at every locus in all members of population, population: indv of same species that live in same area, interbreed, produce fertile offspring
"A sixth mass extinction may be currently underway." Explain this statement
Habitat destruction is threatening many species with extinction. Over 1000 species extinct in last 400 years = 100 to 1,000 times typical background rate seen in fossil record. Habitat destruction through mining, harvesting timber, and development has replaced over hunting as greatest threat to species survival. Consequences of Mass Extinctions • Fossil record shows it takes 5 to 10 million years for diversity of life to recover from a mass extinction • Even longer, 100 million years, after Permian
Describe the significance of recent research on the differences between insect and crustacean Ubx genes
New developmental genes arising after gene duplication events very likely facilitated the origin of novel morphological forms. But since other genetic changes also may have occurred at such times, it can be difficult to establish causal links between genetic and morphological changes that occurred in the past. This difficulty was sidestepped in a recent study of develop- mental changes associated with the divergence of six-legged insects from crustacean-like ancestors that had more than six legs. In insects, such as Drosophila, the Ubx gene is expressed in the abdomen, while in crustaceans, such as Artemia, it is expressed in the main trunk of the body. When expressed, the Ubx gene suppresses leg formation in insects but not in crustaceans. To examine the workings of this gene, researchers cloned the Ubx gene from Drosophila and Artemia. Next, they genetically engineered fruit fly em- bryos to express either the Drosophila Ubx gene or the Arte- mia Ubx gene throughout their bodies. e Drosophila gene suppressed 100% of the limbs in the embryos, as expected, whereas the Artemia gene suppressed only 15%. The researchers then sought to uncover key steps involved in the evolutionary transition from a crustacean Ubx gene to an insect Ubx gene. eir approach was to identify mutations that would cause the Artemia Ubx gene to suppress leg forma- tion, thus making the crustacean gene act more like an insect Ubx gene. To do this, they constructed a series of "hybrid" Ubx genes, each of which contained known segments of the Drosophila Ubx gene and known segments of the Artemia Ubx gene. By inserting these hybrid genes into fruit fly embryos (one hybrid gene per embryo) and observing their effects on leg development, the researchers were able to pinpoint the exact amino acid changes responsible for the suppression of additional limbs in insects. In so doing, this study provided ev- idence linking a particular change in the nucleotide sequence of a developmental gene to a major evolutionary change: the origin of the six-legged insect body plan
List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium
No mutations, random mating, no natural selection, extremely large population size, no gene flow
Describe the contributions that A. I. Oparin, J. B. S. Haldane, Stanley Miller, and Harold Urey made toward developing a model for the abiotic synthesis of organic molecules. Describe the conditions and locations where most of these chemical reactions likely occurred on the early Earth
Oparin and Haldane thought that Earth's atmosphere was a reducing environment, or constantly adding electrons. The energy could have come from lightning and intense UV radiation. They thought that organic molecules came from oceans. Miller and Urey, created a lab experiment, mimicking conditions of Earth's beginnings, which produced organic compounds. They discovered that early atmosphere was made up mostly of nitrogen and carbon dioxide, and that the first organic compounds originated from volcanoes and deep-sea vents
Describe the mass extinctions that ended the Permian and Cretaceous periods. Discuss a hypothesis that accounts for each of these mass extinctions, and summarize the evidence for each hypothesis
Permian Extinction • Permian = 251 mya • Occurred over a time period of maybe a few thousand years to no more than 5 million years • Period of most extreme volcanism in last half billion years • Mass CO2 released → global warming → slows mixing of ocean water → reduced O2 in ocean water Cretaceous Extinction • Cretaceous mass extinction = about 65.5 mya • Lost over 50% of marine species, many families of terrestrial plants & animals, including most dinosaurs • Collision creates huge cloud of debris that would have blocked sunlight and changed global climate • Crater in Yucatan peninsula in Mexico? • Clue is a layer of iridium in sediments around the world
