BYU Biology Exam #3
2. What is natural selection and how does it operate?
...Natural selection - the differential survival and reproduction of individuals in a population. - the process by which populations adapt to their changing environment. - more of natural selection in Chapter 10
7. What is a vestigial trait? Do humans have them?
...Non-functional features - represent a vestige, or remainder, or our biological heritage. Yes humans have them - We have a tailbone but no tail. Goosebumps - remainders of our relatives' hairier bodies.
12. What is radiometric dating and how does it work?
...Radiometric dating - Scientists can determine the date when an ancient fossil organisms lived by estimating the age of the rock that surrounds the fossil. Radiometric dating relies on radioactive decay, which occurs as radioactive elements in rock spontaneously break down into different, unique elements known as daugter products. Each radioactive element decays at its own unique rate. The rate of decay is measured by the element's half life. Has been used to estimate the age of the earth and time of origin of various organisms.
12. What is the 'out of Africa' hypothesis?
...Whether homo sapiens evolved just once, in Africa.
6. How diverse is the subgroup of invertebrates in kingdom Animalia?
..From sponges to the more recent chordates.
10. Who is Lucy? Be able to characterize the evolution of the hominid line.
Hominin(human and human ancestors) fossil discovered in 1974 in Ethiopia - remarkably (most complete ever found of her kind) complete skeleton of the species australopithecus afarensis - Indicated that she walked upright. Evolution of the hominid line - Humans and Human ancestors. First Hominin Ancestor Australopithecus anamensis Australopithecus afarensis (3.5 mil yrs ago) Australopithecus africanus (2.8 mil yrs ago) Homo habilis (1.7 mil yrs ago) Homo sapiens (today)
6. What is the concept of homology? How is it present in organisms' development? in biochemistry?
Homology - the less-obvious similarities between animals in anatomy, behavior, or genes. - ex - the bones in the forelimbs of bats, lions, chimps, humans are all similar. Homology = the similarity in characteristics that has resulted from common ancestry. How is it present in organisms development - fingers and tailbones? The similarity in underlying structure despite great differences in function is evidence of shared ancestry.
16. What is genetic drift? What mechanisms cause this?
...A change in allele frequency that occurs due to chance is called genetic drift. Human populations tend to travel and colonize new areas, and so we seem to be especially prone to evolution via genetic drift. Genetic drift occurs in three different situations - Founder Effect - Bottleneck Effect - Small Populations
11. What is the morphological species concept?
...A species is defined as a group of individuals with some reliable physical characteristics distinguishing them from all other species. Individuals in the same species have similar morphology - they look alike in some key feature. Set of unique physical characteristics that is not found in other groups of organisms. Do we need to know pros and cons?? - chart on page 291
7. What role has adaptive radiation played in the development of members of Plantae?
...Adaptive radiation - the rapid expansion of flowering plants. - the diversification of one or a few species into a large and varied group of descendant species. - typically occurs either after the appearance of an evolutionary breakthrough in a group of organisms or after the extinction of a competing group. - The radiation of flowering plants must be due to an evolutionary breakthrough - some advantage they had over other plants allowed them to assume roles that were already occupied by other species.
3. What is artificial selection? How is it different than natural selection?
...Artificial Selection - Selection imposed by human choice is called artificial selection. It is artificial in the sense that humans deliberately control the survival and reproduction of individual plants and animals with favorable characteristics to change the characteristics of the population.
20. The text states that two unrelated individuals of the 'black race' are no more likely to be biologically similar than a black and white person. How can that be?
...Because racial categories are socially meaningful not biologically. Scientific data indicates that the racial categories on her census form are biologically meaningless.
2. Know what the biological species concept is.
...Biological Species Concept - A species is defined as a group of individuals that, in nature, can interbreed and produce fertile offspring but cannot reproduce with members of other species.
6. What is combination drug therapy? what problems are associated with it?
...Combination drug therapy - also called drug cocktail therapy, is commonly used on diseases for which resistance to a single drug can develop rapidly. The greater the number of drugs used, the greater the number of changes that are required in the bacterial genome for resistance to develop. Problems associated with it - ?
8. What is a stem cell? What is all the excitement about regarding stem cell research?
...Don't perform a specific function but are able to produce many different kinds of cells and tissues, a.k.a. undifferentiated, allowing them to be pressed into becoming many different cell types. Excitement: Could grow organs to replace damaged or defective ones, thus extending a life
7. What is gene therapy? What is the difference between germ-line gene therapy and somatic cell gene therapy?
...Gene Therapy - practice of replacing defective human genes (or their protein products) with functional genes germ-line therapy: supplying the embryo with a normal version of a defective gene. Germ-line gene therapy would ensure that the embryo and any cells produced by cell division would replicate the new, functional version of the gene. somatic cell gene therapy: performed on body cells to fix or replace the defective protein in only the affected cells. A functional version of a defective gene is introduced into an affected individual cell in the laboratory, allowed to reproduce, and then place copies of the cell bearing the corrected gene into the diseased person.
5. What effects might GM foods have on health? Why are people unhappy with GM foods?
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1. CHAPTER 8 - Genetic Engineering Define mutation, neutral mutation, frameshift mutation.
. Mutation - Changes to the DNA sequence, called mutations, can affect the order of amino acids incorporated into a protein during translation. Mutations to a gene can result in the production of different forms, or alleles of a gene. Can result in the production of either a nonfunctional protein or a protein different from the one previously required. Neutral Mutation - Mutations that have no effect on a protein is a neutral mutation. ex - A mutation that changes the mRNA codon from ACU to ACC will have no impact because both of these codons code for the amino acid threonine. Frameshift Mutation - Inserting or deleting a single nucleotide can have a severe impact since the addition(or deletion) of a nucleotide can change the groupings of nucleotides in every codon that follows. All nucleotides located after an insertion or deletion will be regrouped into different codons, producing a frameshift mutation. Ex. - inserting an extra letter "H" after the fourth letter of the sentence, "The dog ate the cat" would change the reading frame to the nonsensical statement, "The dHo gat eth eca t"
Chapter 12 - Prospecting for Biological Gold 1. How many species do scientists estimate exist in the world? How are the various types of species catalogued and archived?
...
2. What is biological classification? How many kingdoms are presently recognized and what are they? What are basic characteristics of each as well as an example?
... ???? Biological Classification - Stematists work in the field of biological classification, in which they attempt to organize biodiversity into discrete and logical categories. analogy - book-cataloguing system in libraries - fiction, non fiction, specific areas. 5 Kingdoms - -Bacteria and Archae - prokaryotes - do not contain nucleus - unicellular - each cell is an organism - 3.465 billion years old -Protista - Made up of the simplest known eukaryotes - most are single-celled creatures but some are multicellular. - 2 billion years old - has organisms that resemble animals, fungi, plants -Animalia - 600/530 million years ago - Cambrian explosion - -Fungi -Plantae
CHAPTER 9 - Where did we come from? 1. Be able to define biological evolution, a species, a biological population.
......Biological evolution - A change in the characteristics of a population of organisms that occurs over the course of generations. The changes in populations that are considered evolutionary are those that are inherited via genes. Species - A species consists of a group of individuals that can regularly breed together, producing fertile offspring, and that is generally distinct from other species in appearance or behavior. Biological populations - Most species are subdivided by geography into smaller groups, or biological populations, that are somewhat independent of other populations.
2. What are Darwin's 4 observations upon which the theory of natural selection is based? Be able to briefly explain how each affects evolution of an organism.
...1. Individuals within Populations Vary. - People come in enormous variety of shapes, sizes and colors - ex - gray wolves born black, tawny, or reddish color - flowers may vary in blooming time, with some individual plants blooming much earlier than others of the same species. 2. Some of the Variation Among Individuals Can Be Passed on to Their Offspring - Darwin noted that breeders could create flocks of pigeons with fantastic traits by using as parents of the next generation only those individuals that displayed these traits. 3. Populations of Organisms Produce More Offspring Than Will Survive - ex. the trees in the local park make literally millions of seeds every summer. Only a few of the much smaller number that sprout live for more than a year or two. 4.Survival and Reproduction Are Not Random - The relative survival and reproduction of 1 variant compared to others in the same population is referred to as its fitness. Traits that increase an individual's fitness in a particular environment are called adaptations. Individuals with adaptations to a particular environment are more likely to survive and reproduce than are individuals lacking such adaptations - ex. Bill depth of finches in Galapagos islands. The closer the bill depth was to 10.1 when the drought hit survived.
4. What are the 3 common misunderstandings regarding natural selection?
...1.The Relationship between the individual and the population 2. The limitations on the traits that can be selected 3. The ultimate result of selection --Natural Selection cannot cause new traits to Arise. One mistaken idea about natural selection is that certain species are doomed to extinction because they "will not" adapt to a new environment. Polar bears are threatened with extinction because they rely on sea ice for hunting, and sea ice in the Arctic is rapidly diminishing as a result of global warming. Why don't they just switch to another food? After all, grizzly bears eat a wide variety of foods. The idea that species "should" change to survive results from our understanding of the selection process of business. ---Natural Selection Does Not Result in Perfection Natural selection does cause populations to become better fit to their environment, but the result of that process is not necessarily "better" organisms that can survive over a wider range of conditions - simply organisms that are better adapted to the current situation. Changes in traits that increase survival and reproduction in one environment may be liabilities in another environment. In other words, most adaptations are trade-offs between success in one situation versus another. ---Natural Selection Does Not Cause Progression Towards a Goal. You may have heard natural selection described as "survival of the fittest"; however it is important to recognize that natural selection favors those variants with the most appropriate adaptions to the CURRENT environment. The survivors are not fittest in an absolute sense, only relative to others in the same population.
9. What is convergent evolution? Give an example?
...Convergent evolution - Evolution of same trait or set of traits in different populations as a result of shared environmental conditions rather than shared ancestry. Will come more later in CH 11.
5. What are directional, stabilizing, and diversifying selection?
...Directional Selection - causes the population traits to move in a particular direction. Directional Selection is typically the type of selection that leads to change in a population over time. ex. experienced by the flies in the alcohol-laden environment. Stabilizing Selection - The extreme variants in a population are selected against and the traits of the population stay the same. The average variant in the population may have the highest fitness. ex. humans - the survival of newborns is correlated to birth weight - both extremely small and large babies are selected against. Diversifying selection - Causes the evolution of a population consisting of 2 or more variants. Diversifying selection is especially likely if different subpopulations are experiencing different environmental conditions. ex. one type of pollinator specializes in pale flowers, one in dark flowers = high fitness. neither pollinator chooses intermediate color = low fitness
7. Is it possible for any humans to be HIV resistant?
...For the human population as a whole to become resistant to this virus, nonresistant variants must die out of the population Because a majority of nonresistant people are not ever even exposed to this virus they will continue to survive and reproduce and thus the nonresistant variants will probably never be lost from the population
11. How does the fossil record support evolutionary theory? How are fossils created?
...Fossils form when the organic material in bone decomposes and minerals fill the space left behind. This is more likely to occur when dead organisms are quickly buried by sediment (water, mud, sand, or volcanic ash). Fortunately for scientists looking for fossils of hominins - these organisms were likely to live near water and be rapidly buried, so their fossil record provides a compelling record of evolutionary history. How the fossil record supports evolutionary theory - We find fossils and are able to date them to give us a road map of migration and evolution of species. Charles Darwin used this approach to find evidence that humans and apes are relatives. (thought the fossils could be found in Africa) [Pg. 240].
17. What is the founder effect? Bottleneck effect?
...Founder Effect - Sampling error is more severe for smaller subsets of a population, such as those that typically found new settlements. This type of sampling error is often referred to as the founder effect. A small sample of a large population establishes new population. Bottleneck Effect - A dramatic but short lived reduction occurs in population size - followed by a rapid increase in population. - may happen as a result of natural disasters. In Both the new population differs from the original because the gene pool of the survivors is not an exact model of the source population's gene pool.
5. What is gamete incompatibility? interspecies hybrids?
...Gene Flow - The spread of an allele throughout a species' gene pool is called gene flow. Gene flow cannot occur between different biological species because pairing between them fails to produce fertile offspring Prefertilization Barriers: prevent fertilization from occuring ------Spatial Isolation - They never contact each other, separated by a distance - ex. Polar bear(arctic) and spectacled bear (south america) ------Behavioral Isolation - Ritual behaviors that prepare partners for mating are different in different species - ex. many birds with premating songs and or dances ------Mechanical Isolation - Sex organs are incompatible between different species, so sperm cannot reach egg. - many insects with "lock and key" type genitals ------Temporal Isolation - Timing of readiness to reproduce is different in different species - ex. Plants with different flowering periods ------Gamete Incompatibility - Proteins on egg that allow sperm binding do not bind with sperm from another species. ex. Animals with external reproduction, such as sponges. - most common prefertilization barrier between species that will mate with each other is an incompatibility between eggs and sperm. interspecies hybrids - Interspecies hybrids= The offspring of parents from 2 different species--die before birth because...placing genes from different species together provides a hybrid offspring with incomprehensible information about how to build a body. Thus, normal development cannot take place. ------Postfertilization barriers: --Hybrid inviability - zygote cannot complete development because genetic instructions cincomplete - ex - a sheep crossed with a goat can produce an embryo, but it dies in the early developmental stages. --Hybrid Sterility - Hybrid organism cannot produce offspring because Chromosome numer is odd - ex. Mules
9. What is the genealogical species concept? what species are examples of this?
...Genealogical species concept - a species is defined as the smallest group of reproductively compatible organisms containing all of the known descendants of a single common ancestor. emphasizes unique evolutionary lineages; thus it greatly increases the number of identifiable species. ex. The spotted owl - single species with 3 distinct populations: northern, Californian, Mexican. ??
8. What is gradualism? How about punctuated equilibrium?
...Gradualism - Darwin assumed that speciation occurred over millions of years as tiny changes gradually accumulated. Punctuated equilibrium - Most speciation events are sudden, result in dramatic changes in form within the course of a few thousand years, and are followed by many thousands or millions of years of little change
14. Why do human groups differ? What role does natural selection play in this?
...Humans are not true biological races. However human populations do differ from each other in many traits. Natural selection favors individuals who carry 1 copy of sickle-cell allele in particular environments. Allele is an adaptions - a feature that increases fitness within populations in malaria-prone areas. Natural selection - nose form - populations in dry climates tend to have narrower noses than do populations in moist climates. A long narrow nose has a greater internal surface area, exposing inhaled air to more moisture, reducing lung damage and increasing the fitness of individuals in dry environments. Flattened broad noses are more common in warm, wet environments.
19. What is assortative mating and how has it contributed to differences among races?
...Individuals prefer to marry someone who is like themselves, by a process called positive assortative mating. For example there is a tendency for people to mate assortatively by height - tall women tall men, and by skin color.
18. How does sexual selection influence mating strategies? How has it possibly added to the differences among human races?
...Men and Women within a population may have preferences for particular physical features in their mates. These preferences can cause populations to differ in appearance. When a trait influences the likelihood of mating, that trait is under the influence of a form of natural selection called sexual selection. In humans, there is some evidence that the difference in overall body size between men and women is a result of sexual selection - a widespread female preference for larger males - size because it may be an indication of overall fitness.
13. Why do the authors reject the static, transformation, and separate types hypotheses for the origins of life and the diversity of life forms we see today?
...Rejection of Static Hypothesis - Clearly rejected - Radiometric dating indicates that Earth is far older than 10,000 years, and the fossil record provides unambiguous evidence that the species that have inhabited this planet have changed over time. Transformation Hypothesis - Rejected because it is the poorest explanation of these observations - if organisms arose separately and each changed on its own path, there is no reason to expect that different species would share structures - especially if these structures are vestigial in some of the organisms. There is also no reason to expect similarities among species in DNA sequence. The hypothesis of transformation predicts that we will find little evidence of biological relationships among living organisms. As our observations have indicated, evidence of relationships abound. Separate types Hypothesis - Rejected - Both Separate types hyp and common descent hyp contain a process by which we can explain observations of relationships. The difference between the two theories is that common descent hypothesizes a single common ancestor for all living things, while separate types hypothesizes that ancestors of different groups arose separately and then gave rise to different types of organisms. Separate types seems more reasonable than common descent to many people. It seems impossible that organisms as different as pine trees, mildew, ladybugs, and humans share a common ancestor. However, several observations indicate that these disparate organisms are all related. The MOST compelling evidence for the single origin of all life is the universality of both DNA and of the relationship between DNA and proteins.
21. Why does the US Census Bureau bother to record race as part of each census?
...Socially meaningful. The U.S. Government collects information about race on the census form as part of its effort to measure and ameliorate the lingering effects of historical, state-supported racism, but on its form, the census Bureau acknowledges that the races with which people identify "should not be interpreted as being primarily biological or genetic"
5. What does 'special creation' and intelligent design? Understand the static, transformation, separate types, and common decent hypotheses?
...Special Creation - God created organisms during the 6 days of creation described in the first book of the Bible, Genesis. Organisms, including humans, have not changed significantly since creation. Genesis story indicates that creation also occurred fairly recently, within the last 10,000 years. Intelligent Design - Static model hypothesis - The assertion that organisms came into being within the last 10,000 years and that they have not changed substantially since their creation is testable through observations of the natural world. Hypothesis about the origin and relationships among living organisms - indicates that organisms are recently derived and unchanging. Transformation hypothesis - All living organisms were created, perhaps even millions of years ago, and that changes have occurred in these species but brand-new species have not arisen. Separate-types hypothesis - Different types of organisms (for example, plants and animals with backbones) arose separately and since their origin have diversified into numerous species; Common descent hypothesis - species do change over time, and new species can arise. All species derive from a common ancestor.
6. How does the process of speciation occur?
...Speciation - the Evolution of 1 or more species from an ancestral form is called speciation 3 Steps: 1. Isolation of the gene pools of subgroups, or populations of the species; 2. Evolutionary changes in the gene pools of 1 or both of the isolated populationsl 3. The evolution of reproductive isolation between these populations, preventing any future gene flow.
CHAPTER 11 - Who am I? 1. What is a species, genus, subspecies? Is subspecies the same as race?
...Species - A group whose members have the greatest resemblance Genus - 2 Part name assigned to each species - the first part of the name indicates the genus, or broader group Subspecies - Modern biologists added, to distinguish modern humans from earlier humans who appeared approximately 250,000 years ago Is subspecies the same as race??
13. Why are human races not biological groups? What evidence is there that this is true? (that they are NOT separate biological groups).
...Test: if a race has been isolated from other populations of the species for many generations, it should have these two traits: 1. Some unique alleles. 2. Differences in allele frequency for some genes relative to other races Sickle cell anemia. - was long thought of as a black disease. There are whites and asians with sickle cell anemia and many blacks that dont have it. not unique to blacks. Cystic fibrosis - was thought to be a white persons disease. false.
8. Be able to explain biogeography and how it relates to the evolution of life?
...The distribution of species on Earth is known as the biogeography of life. ?
7. What is the founder hypothesis? How does it lead to allopatric populations? What are sympatric species?
...The establishment of a new population far from related species may lead to the evolution of several new species - According to this hypothesis the diversity of unique species on oceanic islands, as well as in isolated bogs, caves, and lakes, resulted from colonization of these once "empty" environments by 1 species that rapidly speciated, taking advantage of many different resources. Ex. more than 50 species of silversword are now found on the hawaiian islands - all descendants from the original founding population. How does it lead to allopatric populations? Populations that are isolated from each other by distance or a barrier are known as allopatric. - The geographic pattern indicates that each population descended form ancestral species that each had been separated into 2 populations. What are sympatric species? Separation between two populations' gene pools may ovvur even if the populations are living near each other, that is, if they are sympatric.
4. What is gene flow? What is spatial, behavioral, mechanical, and temporal isolation?
...The spread of an allele throughout a species' gene pool What is spatial, behavioral, mechanical, and temporal isolation? Spatial: separated by distance Behavioral: differences in mating behavior Mechanical: the sexual organs of 2 individuals are incompatible Temporal: timing of reproduction (flowering plants)
4. What is the hypothesis of common descent? What evidence is there for it?
...The theory of common descent states that all modern organisms descended from a single common ancestor. - species do change over time, and new species can arise. All species derive from a common ancestor. Evidence - " The Origin of Species" - The biological classification system in Darwin's era. - Anatomical similarities among species - organisms that look quite different have suprisingly similar structures - - Useless traits in modern species - flightless birds producing functionless wings - Shared developmental pathways - Early embryos of Snakes to Humans look very similar. - DNA Similarities - The distribution of organisms on Earth - Darwin noticed on each island in the Galapagos had a unique species of mockingbird. - Fossil evidence - progression from more ancient forms to more modern forms - horses.
3. Be familiar with the theory of evolution (carryover from the last test).
...The theory of evolution is a principle for understanding how species originate and why they have the characteristics that they exhibit. The theory of evolution can thus be stated: "All species present on Earth today are descendants of a single common ancestor, and all species represent the product of millions of years of accumulated microevolutionary changes."
CHAPTER 10 - An evolving enemy, natural selection 1. What is turburculosis? How is it expressed? How is it transmitted?
...Tuberculosis is caused by the single-celled bacterium mycobacterium tuberculosis. Tuberculosis is a threat not because it is an especially deadly infection, but instead because it affects so many people. 90% are symptomless. Transmitted - almost entirely from people with active disease - cough, sneeze, speak, or spit, they expel infectious droplets. Prolonged, frequent, or intense contact with those that have it. Expressed - Symptoms? - cough that produces blood, fever, fatigue, long relentless wasting in which the patient becomes weaker and thinner - consumes people from within.
3. What does it mean to be reproductively isolated?
...When gene flow can't occur between different biological species because pairing between them fails to produce fertile offspring.
10. What are the 6 main races of humans? Are they 'valid' races in the strict biological sense? Why?
...White, Black, Pacific Islander, Asian, Australian Aborigine, and Native American. Do these groups show the predicted pattern of race-specific alleles and unique patterns of allele frequency? no. No Race-specific Alleles have been identified.
15. Why is skin color in humans an example of convergent evolution?
...environmental conditions rather than shared ancestry When scientists compare the average skin color in a native human population to the level of ultraviolet light to which that population is exposed they see a close correlation -- the lower the UV light level, the lighter the skin.
5. What is the endosymbiotic theory for the origin of Protists?
...modern eukaryotes are most likely the descendants of a confederation of these primitive eukaryotes with other prokaryotic cells. Mitochondria and cholorplasts appear to have descended from bacteria that took up residence inside larger primitive eukaryotes. When organisms live together, the relationship is known as symbiosis. In this case the relationship was mutually beneficial, and over time, the cells became inextricably tied together.
4. How do the domains Bacteria and Archaea differ?
..Structure of its cell membranes - Archaea are typically found in extreme environments, including high-salt, high-sulfur, and high temp habitats. Taq polymerase belongs to Archaea - operates at high temperatiures.
3. How is a gene cloned using bacteria? What are the main steps
.Bacteria with the BGH gene can serve as factories to produce millions of copies of this gene and its protein product. 1. Remove the Gene from the Cow Chromosome. 2. Insert the BGH Gene into the Bacterial Plasmid 3. Insert the Recombinant Plasmid into a Bacterial Cell.
4. What qualifies as a GM food?
.Genetically modified -Most soybeans grown are modified for herbicide resistance -GM corn - an ingredient in most processed foods - is common as well -GM canola and cottonseed oils are used in a huge range of food products Genetically modified foods are foods derived from genetically modified organisms (GMOs). Genetically modified organisms have had specific changes introduced into their DNA by genetic engineering techniques. These techniques are much more precise than mutagenesis (mutation breeding) where an organism is exposed to radiation or chemicals to create a non-specific but stable change. Genetically modified plants are plants whose DNA is modified using genetic engineering techniques. In most cases the aim is to introduce a new trait to the plant which does not occur naturally in this species. Examples include resistance to certain pests, diseases or environmental conditions, or the production of a certain nutrient or pharmaceutical agent. (soybean, corn, canola, rice, and cotton seed oil.)
9. Have humans ever been cloned? If natural, why are people opposed to cloning of humans?
.Only via the natural spontaneous production of identical twins. --It would probably include selecting the traits an individual will possess.
2. How is gene expression regulated by the cell?
.Turning a gene on or off, or modulating it more subtly, is called regulating gene expression. Regulation of Transcription - Gene expression is most commonly regulated by controlling the rate of transcription. Prokaryotic cells typically regulate gene expression by blocking transcription via proteins called repressors that bind to the promoter and prevent the RNA polymerase from binding. When the gene needs to be expressed the repressor will be released from the promoter so that the RNA polymerase can bind. Eukaryotic cells - enhance gene expression using proteins called activators that help the RNA polymerase bind to the promoter, thus facilitating gene expression. Regulation by Chromosome Condensation - Regulate gene expression by condensing all or part of a chromosome. Regulation by mRNA degradation - Eukaryotic cells can also regulate the expression of a gene by regulating how long a messenger RNA is present in the cytoplasm. Enzymes called nucleases roam the cytoplasm, cutting RNA molecules by binding to one end and breaking the bonds between nucleotides.
6. What are examples as to why scientists would want to GM a crop?
.increase their yield and shelf life, decrease the need for pesticides
3. How long ago do scientists believe life first began on earth?
4 billion years ago...
