Evolution and Ecosystems

Question 1

1. Describe and Explain the endosymbiotic theory

Answer 1

It is thought that life arose on earth around four billion years ago. The endosymbiotic theory states that some of the organelles in today’s eukaryotic cells were once prokaryotic microbes. In this theory, the first eukaryotic cell was probably an amoeba-like cell that got nutrients by phagocytosis and contained a nucleus that formed when a piece of the cytoplasmic membrane pinched off around the chromosomes. Some of these amoeba-like organisms ingested prokaryotic cells that then survived within the organism and developed a symbiotic relationship. Mitochondria formed when bacteria capable of aerobic respiration were ingested; chloroplasts formed when photosynthetic bacteria were ingested. They eventually lost their cell wall and much of their DNA because they were not of benefit within the host cell. Mitochondria and chloroplasts cannot grow outside their host cell.

Question 2

Summarize the evidence in support of the theory for the evolution of eukaryotic cells.

Answer 2

• Chloroplasts are the same size as prokaryotic cells, divide by binary fission, and, like bacteria, have Fts proteins at their division plane. The mitochondria are the same size as prokaryotic cells, divide by binary fission, and the mitochondria of some protists have Fts homologs at their division plane.
• Mitochondria and chloroplasts have their own DNA that is circular, not linear.
• Mitochondria and chloroplasts have their own ribosomes that have 30S and 50S subunits, not 40S and 60S.
• Several more primitive eukaryotic microbes, such as Giardia and Trichomonas have a nuclear membrane but no mitochondria

Question 3

2. explain how fossils are dated. Explain the significance of leading fossils.

Answer 3

One of the most common technique is radiometric dating which is based on the decay of radioactive isotopes. Each radioactive isotope has a fixed rate of decay. An isotope’s half-life, the number of years it takes for 50 percent of the original sample to decay, is unaffected by temperature, pressure, and other environmental variables. Fossils contain isotopes of elements that accumulated in the organisms when they were alive, E.g., the carbon in a living organism includes the most common carbon isotope, carbon-12, as well as a radioactive isotope, carbon-14. When the organism dies, its stops accumulating carbon, ad the carbon-14 that it contained at the time of death slowly decays and becomes another element, nitrogen 14.Thus, by measuring the ratio of carbon-14 to total carbon or to nitrogen-14 in a fossil, we can determine the fossils age.

Question 4

3. explain why living fossils did not undergo much change and give examples.

Answer 4

At the time of death, the organism got , causing their bodies (or in some cases their bones) to be extremely well preserved so that they could maintain their structure for hundreds of years, where they were found by humans. 
Methods of preservation include: 
o	Silicification/ petrification (Silifizierung bzw. Verkieselung/ Versteinerung): silica (Kieselsäure) from weathered volcanic ash is gradually incorporated into partly decayed wood 
o	Phosphitylation (Phosphatierung): bones and teeth are preserved on phosphate deposits 
o	Pyritization (Verkiesung): pyrite (Pyrit) replaces hard remains of the dead organism 
o	Tar pit (Teergrube): animals fall into and are trapped in mixture of tar and sand 
o	Trapped in amber (Bernstein): gum (Harz) from conifers traps insects and then hardens 
o	Limestone (Kalkstein): calcium carbonate from the remains of marine plankton is deposited as a sediment that traps the remains of other sea creatures

Question 5

4. explain the significance of transitional fossils and give examples (i.e., Archaeopteryx)

Answer 5

Transitional fossils (“missing/ connecting links“) (= Übergangs-/ Mosaik-/ Brückenform) are intermediate forms that show traits of two different taxonomic groups. They suggest that one (original) group may have given rise to the other (newly developing) group by evolutionary processes. One of the main examples is the Archaeopteryx, the most primitive bird known. It serves as a transitional fossil between the dinosaur and the modern bird, with it sharing jaws with sharp teeth, a forelimb with three fingers with grasping claws, a long bony tail and various other skeletal features putting it in closer relation to the dinosaur than a bird, with the Archaeopteryx only possessing a bird’s small size, broad wings, and an ability to fly or glide.

Question 6

5. describe and explain molecular biological (e.g., DNA hybridization) methods that can be used to determine phylogenetic relationships.

Answer 6

A phylogenic relationship means that the two species in question that do share a phylogenic relationship have had a common ancestor in their past.
DNA hybridization
1. first the DNA of each source is extracted, and the two strands are separated (denatured) by heat treatment => hydrogen bonds are broken 2.the single strands of the two sources are then put together, whereupon they join up (hydrogen bonds are formed between complementary bases), sometimes with the complementary strand from their own source, but sometimes with the complementary strand from the other source (forming hybrid DNA) 3.the double-stranded hybrid DNA containing strands from the two sources will separate at a lower temperature, because the hydrogen bonding which holds the two strands together is weaker, as some of the bases fail to pair
4.the two sources are thought to be more closely related, the closer the temperature at which the hybrid DNA separates is to the temperature used to separate the DNA of the two sources (great similarity of base sequence => more hydrogen bonds form) => crude measure of DNA relatedness!

Question 7

5. describe and explain immunological (e.g., precipitation test) methods that can be used to determine phylogenetic relationships.

Answer 7

A phylogenic relationship means that the two species in question that do share a phylogenic relationship have had a common ancestor in their past.
1.A laboratory animal (e.g., a rabbit) is injected with human serum.
2.The rabbit then produces antibodies in response to the human serum proteins.
3. These antibodies react with the serum proteins of various vertebrates with precipitations of different intensities.
The extent of precipitation with the human serum in response to which the antibodies have been formed is taken to be 100%. The varying degree of precipitation illustrates the match between the surface proteins of the serum and the antibodies. The degree of precipitation is a measure of the extent to which the tested serum proteins are congruent with the human serum proteins; correspondingly, this is interpreted as an indication of the similarity of the responsible genes and therefore a measure of the relationship between the organisms tested, i.e., their common origin. On a biochemical level, these proteins are homologous (having the same relation, position, or structure)-

Question 8

6. describe and explain how the recorded genetic changes in living organisms over many generations can be used as evidence of evolution.

Answer 8

o Anatomy. Species may share similar physical features because the feature was present in a common ancestor (homologous structures).
o Molecular biology. DNA and the genetic code reflect the shared ancestry of life. DNA comparisons can show how related species are.
o Biogeography. The global distribution of organisms and the unique features of island species reflect evolution and geological change.
o Fossils. Fossils document the existence of now-extinct past species that are related to present-day species.
o Direct observation. We can directly observe small-scale evolution in organisms with short lifecycles (e.g., pesticide-resistant insects).
To adapt to a certain environment, a species will genetically alter itself (and its appearance) to better be adapted to its environment. An example is the peppered moth population found in England at the time of the industrial revolution. Due to the fact that the surplus of factories was spewing out excessive amounts of pollution, the surrounding forests got covered in a layer of soot. This left the natural-coloured moths in a precarious position, as their light brown colour left them highly visible in the surrounding darkened forest, making them easy prey. Through genetic variation they adapted, splitting into a darkened moth and a light moth. This change was genetic. Because the light moths were even more of a target, they soon went extinct. But because the dark moths were more suited to the sooted environment, they were able to survive due to their more advantageous genetic traits. Evolution occurred.

Question 9

7. discuss the significance of vestigial organs as indicators of evolutionary trends

Answer 9

These ‘useless’ body-parts, otherwise known as vestigial organs, are remnants of lost functions that our ancestors possessed. They once represented a function that evolved out of a necessity for survival, but over time that function became non-existent. Since those useless body parts aren’t needed anymore, a lack of vestigial organs would imply that the organism developed further, evolution occurring because the new environment does no longer require the vestigial organs.

Question 10

8. describe and explain the biogeographical evidence of evolution.

Answer 10

The distribution of organisms around the world lends powerful support to the idea that modern forms evolved from ancestral populations. Biogeography is the study of the geographical distribution of species, both present-day and extinct. It stresses the role of dispersal of species, a point of origin across pre-existing barriers. Studies from the island populations indicate that flora and fauna of different islands are more closely related to adjacent continental species than to each other.

Question 11

9. use given data to draw a cladogram or interpret it.

Answer 11

A cladogram gives a hypothetical picture of the actual evolutionary history of the organisms. A cladogram indicates the relationships between organisms descended from a common ancestor. The temporal aspect of a phylogenetic tree, however, is missing from a cladogram.

1. Find the outgroup (the “odd one out”)
2. Proceed along the line, always trying to find one species that differs from the rest
3. Create branches that illustrate the differentiation of one species from the rest

Question 12

9. use given data to draw a phylogenetic tree or interpret it.

Answer 12

A Phylogenic tree gives an actual representation of the evolutionary history of the organisms.

1. Find the outgroup (the “odd one out”)
2. Proceed along the line, always trying to find one species that differs from the rest
3. Find the temporal order of the species
4. Create branches that illustrate the differentiation of one species from the rest

Question 13

10 describe the hierarchical classification and name the taxonomic categories. Moreover, explain the binominal nomenclature giving an example

Answer 13

In 1748, Swedish botanist and anatomist Carolus Linnaeus published “Systema naturae“, his taxonomic classification of all plants and animals known at the time. Linnaeus introduced scientific names for each species that consisted of two parts:
Example: Panthera (capitalized) pardus (both parts are italicized)
genus + specific epithet unique for each species
(= Gattung) + (= Artepitheton)
-> This two-part format of the scientific name is called binominal nomenclature.
In the Linnaean system, species and genera are grouped further into a hierarchical system of higher taxonomic categories.

Question 14

Hierarchical classification

Answer 14

Hierarchical classification:

• Species (e.g., Homo Sapiens)
• Genus (e.g., Homo)
• Family (e.g., Hominidae)
• Order (e.g., Primates)
• Class (e.g., Mammals)
• Phylum (e.g., Vertebrates )
• Kingdom (e.g., Animals)
• Domain (e.g., Eukarya)

Question 15

10. describe and explain how different species have evolved from a single ancestral species/ a specific trait could have developed according to Lamarck’s theory of evolution

Answer 15

Lamarck: Lamarck believed that organisms are not passively altered by their environment. Instead, a change in the environment causes changes in the needs of organisms living in that environment, which in turn causes changes in their behaviour. Altered behaviour leads to greater or lesser use of a given structure or organ: continued use would cause the structure to increase in size and become more highly developed over several generations, whereas disuse would cause it to shrink or even disappear. Lamarck claimed that such acquired characteristics were heritable. (Today, our understanding of genetics tells us that traits acquired by use during an individual´s life is not inherited!) The result is the continuous, gradual change of all organisms, as they became adapted to their environments; the physiological needs of organisms, created by their interactions with the environment, drive Lamarckian evolution. Lamarck also thought that evolution happens because organisms have an innate drive to become more complex (inneres Bedürfnis, Vervollkommnungstrieb).

Question 16

10. describe and explain how different species have evolved from a single ancestral species/ a specific trait could have developed according to Darwin’s theory of evolution (fundamental ideas if his “theory of evolution by natural selection”)

Answer 16

Darwin:
Natural selection can provide the means for species change over time because natural selection will always favour the most adaptive phenotypes (therefore genotypes) at the time. More favourable phenotypes will have greater reproductive success and will become proportionally more abundant in the population. Over time, favourable phenotypes will predominate, and the unfavourable phenotypes will become exceedingly rare

Question 17

10. describe and explain how different species have evolved from a single ancestral species/ a specific trait could have developed according to the synthetic/modern theory of evolution (aspects that go beyond Darwin’s theory of evolution).

Answer 17

• Variation amongst ancestors of … due to mutations and recombination e.i. some had… and others …
• Individuals with …. had better chances to survive/were better adapted to the environment -> catch more prey/get more food -> “survival of the fittest”
• individuals with …. survive for a long period of time -> “natural selection” -> produce more offspring -> pass on their gene pool shifts -> in the course of generations, individuals will have ….
  Aspects that go beyond Darwin: mutations, recombination, genes OR gene pool

Question 18

11. explain what is meant by fitness and explain how evolution, through adaptation, equips species for survival.

Answer 18

Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it. So, if brown beetles consistently leave more offspring than green beetles because of their color, you will say that the brown beetles had a higher fitness relative to the green beetles. Of course, fitness is a relative thing. A genotype’s fitness depends on the environment in which the organism lives. The fittest genotype during an ice age, for example, is probably not the fittest genotype once the ice age is over. Fitness is a handy concept because it lumps everything that matters to natural selection (survival, mate-finding, reproduction) into one idea. The fittest individual is not necessarily the strongest, fastest, or biggest. A genotype’s fitness includes its ability to survive, find a mate, produce offspring — and ultimately leave its genes in the next generation. Key messages:
• There is a fit between organisms and their environments, though not always a perfect fit.
• Traits that confer an advantage may persist in the population and are called adaptations.
• Inherited characteristics affect the likelihood of an organism’s survival and reproduction.
• Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing.
• Evolution does not consist of progress in any particular direction.
• Fitness is reproductive success - the number of viable offspring produced by an individual in comparison to other individuals in a population/species.

Question 19

12. Describe and explain the biological species concept. Furthermore, describe the limitations of its definition.

Answer 19

A species is a group of actually or potentially interbreeding natural populations that is reproductively isolated from other such groups. Members of a biological species can interbreed in nature and produce viable, fertile offspring.
Question: Are donkeys and horses’ species according to Ernst Mayr´s definition?
Background information:
• mule (Maultier) = horse mare (Stute) + donkey stallion (Hengst)
• hinny (Maulesel) = horse stallion + donkey mare
Answer: Bastards are obviously viable (they exist!), but sterile
-> donkey and horse are different species!!!
Note: Limitations of the biological species concept are:
• it cannot be applied to fossils
• it cannot be applied to asexual organisms such as prokaryotes
• it is difficult to apply the biological species concept to the many sexual organisms about which little is known regarding their ability to mate with different kinds of other organisms
For such reasons, alternative species concepts are useful in certain situations. One of those alternatives is the morphological species concept.

Question 20

13. explain the concept of the gene pool.

Answer 20

Population: localized group of individuals of the same species that are capable of interbreeding and producing fertile offspring
Gene pool: the total sum of all genes presents in a sexually reproducing population
Allele frequency: the proportion of a particular allele of a gene in a population, relative to other alleles of the same gene

Question 21

14. name/define/apply the Hardy-Weinberg law

Answer 21

The Hardy Weinberg law is a mathematical model that can be used to show how the alle frequency in a gene pool determines the frequency of the phenotypes, as well as that the frequencies remain unchanged over various generations, if the conditions of an ideal population are met.
Formula: p^2+2pq+q^2=1
Application:
genotype frequency example: Population of peppered moths of 100 animals; gene pool of 200 alleles, with 120 of them being dark and 80 being bright.
The frequency of allele A in the gene pool is named p, in this case is 120/200=0,6 or 60%. The frequency of allele a is named q and is 80/200=0,4 or 40%. As these are all the alleles that occur in this example, the sum must be 1. The frequencies of the genotypes are a result of the probability allele combinations known from genetic crosses
- the frequency of AA equals q^2, here 0,36
- The frequency of Aa / aA is 2pq, here 0,48
- The frequency off aa equals q^2, here 0,16
-> With the allele frequencies chosen in this example, only 16% of moths will have the lighter wing color, whereas 84% will be dark.

Question 22

compare ideal and real populations

Answer 22

Ideal populations: This only applies if the following conditions are met:

• There are no disadvantages in selection for certain genotypes
• There are no mutations
• No preference of particular genotypes in reproduction
• Complete genetic mixing occurs in the population (panmixia)
• There are no random effects; the population must be large enough so that frequencies reflect probability values
• No immigration or emigration takes place
• > IF these conditions are met the population is ideal, such conditions do not exist in reality. This means that in reality frequencies do not change. A population is therefore permanently changing; evolution is happening. Conversely, all factors that can change the frequencies of alleles can be identified.

Question 23

15. explain how natural selection, genetic drift, gene flow, and mutation alter allele frequencies in a gene pool.

Answer 23

• Natural selection: Differential survival and reproductive success of individuals carrying different genotypes
• Genetic drift: Chance fluctuations in allele frequencies from one generation to the next
• Gene flow: Immigration/emigration of individuals -> transfer of alleles between populations
• Mutation, recombination: random change of genotypes

Question 24

16. Name/describe/explain different types of selective pressure

Answer 24

Selection pressures are external agents which affect an organism’s ability to survive in a given environment

• Selection pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait)
• Selection pressures may not remain constant, leading to changes in what constitutes a beneficial adaptation
• Directional selection is most often associated with evolution (change in the gene pool over time). It changes the characteristics of a population by favouring individuals that vary in one direction from the mean of the population. If directional selection operates over many generations then an evolutionary trend results in the population.
• Disruptive selection changes the characteristics of a population by favouring individuals that vary in both directions from the mean of the population. It may lead to evolution if one (or both) of the phenotype extremes is then subjected to new (different) selection pressures.
• Stabilizing selection preserves the characteristics of a population by favouring average individuals. It reduces variation but does not change the position of the population´s mean.

Question 25

17. Name/explain/discuss a selective advantage in a given example.

Answer 25

The extremely cold and long winter of 1946/47 in central Europe led to a decrease in insect population. A consequence of this was a lack of food for moles. Genetically determined smaller moles had a selective advantage. They managed with less food. Larger specimen was rather prone to starvation. Investigations showed that the proportion of larger animals had declined after that winter

Question 26

18. Identify/name the adaptation in a given example and explain how it enables the organism to be adapted.

Answer 26

In this example the organism in question is an Herbivore (a dinosaur that eats plants). Originally the Herbivore would eat a tree as normal, as both would be the same height. Over time, to stop it being prey to the dinosaur, the tree will raise its crown higher. Because the Dinosaur would then not be able to reach up, it would not be able to get food from the tree. So, in response to it, the dinosaur would also evolve. Through natural selection and many generations, the dinosaur would begin to increase the size of its neck and to strengthen it in order to get to the raised crown. Eventually the dinosaur would be able to get to the crown, so the genetic adaptation would suffice, and the dinosaur would no longer grow.

Question 27

19. describe and explain the role of natural selection in selectively changing genetic variation in a population. Explain stabilizing, directional, and disruptive selection.

Answer 27

A population has variation among its individuals (due to mutation and recombination!). In a particular environment, certain traits are more advantageous than others. The individuals with the advantageous traits are able to survive better and produce more offspring (=> higher reproductive success) => their fitness is greater! In subsequent generations, there are relatively more individuals with the inherited advantageous traits. In this way, the gene pool of the population changes from one generation to the next => the population evolves! Selection is the evolutionary force responsible for adaptation to the environment. (a) Directional selection: shifts the overall makeup of the population by favouring variants at one extreme of the distribution; in this case, darker mice are favoured because they live among dark rocks, and a darker fur color conceals them from predators (b) Disruptive selection: favours variants at both ends of the distribution; these mice have colonized a patchy habitat made up of light and dark rocks, with the result that mice of an intermediate color are at a disadvantage (c) Stabilizing selection: removes extreme variants from the population and preserves intermediate types; if the environment consists of rocks of an intermediate color, both light and dark mice will be selected against

Question 28

20. explain the genetic and evolutionary consequences of the founder effect and the bottleneck effect.

Answer 28

Bottleneck: A sudden change in the environment such as a fire or flood, may drastically reduce the size of a population. In effect, the survivors have passed through a restrictive “bottleneck”, and their gene pool may no longer be reflective of the original population’s gene pool; this is called the bottleneck effect. By chance, certain alleles may be overrepresented among the survivors, others may be underrepresented, and some may be eliminated altogether. Examples include most endangered species, such as the cheetah. Founder: When a few individuals migrate away, or become isolated from a larger population, this smaller group may establish a new population whose gene pool is not reflective of the source population; this is called the founder effect. For example, the founder effect can occur when a few members of a population colonize a new location. These founders pass through an “isolation bottleneck” and represent a distinct gene pool with different allele frequencies from those of the parent population. The colonizing population may evolve differently from that of the parent population, particularly since the environmental conditions for the isolated population may be different.

Question 29

21. explain allopatric speciation in terms of migration, isolation, and adaptation leading to reproductive (genetic) isolation of gene pools.

Answer 29

In allopatric speciation, a new species form while geographically isolated from its parent population. As the isolated population evolves by different mutations, natural selection and genetic drift, reproductive isolation from the ancestral species may arise as a by-product of the genetic change. Such reproductive barriers prevent interbreeding with the parent population, even if the populations come back into contact. Note that the allopatric speciation can also occur without geologic remodelling, such as when individuals colonize a remote area, and their descendants become geographically isolated from the parent’s population (e.g., speciation n the Galapagos Island following colonization by mainland organisms).

Question 30

22. describe and explain mechanisms of reproductive isolation.

Answer 30

Reproductive isolation: the existence of isolation barriers that impeared members of two species from interbreeding and producing viable, fertile offspring). Such barriers block gene flow between the species and limit the formation of hybrids. Reproductive barriers are classified as Prezygotic barriers, impeding mating between species of hinder the fertilization of ova if members of different species attempt to mate. Examples include: Habitat isolation (Two species (e.g., garter snake) occupy different habitats in the same area (Snake 1 lives in the water, snake two is terrestrial), rarely come into contact with one another despite no obvious physical barriers. ) Temporal isolation (Species that breed during different times of the day / different seasons or years cannot mix their gametes.) Behavioural isolation (Courtship rituals of some species designed to attract males of the same species are reproductive barriers, even between closely related species.) Mechanical isolation (Mating is attempted, but morphological differences prevent its successful completion (e.g., Snails being blocked by their shells from aligning their genital openings)) Gametic isolation (Sperm of one species may not be able to fertilize the eggs of another species. For instance, sperm may not be able to survive in the reproductive trace of females of the other species, or biochemical mechanisms may prevent the sperm from penetrating the membrane surrounding the other species eggs.) IF a sperm cell from one species does overcome prezygotic barriers and fertilizes an ovum from another species, postzygotic barriers often prevent the hybrid zygote from developing into a viable, fertile adult. Examples are Reduced hybrid viability (The genes of different parent species may interact in ways that impair the hybrids development or survival in its environment.) Reduced hybrid fertility (If the chromosomes of two parents’ species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since the infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species. (e.g., donkey + horse -> mule)) Hybrid breakdown (Some first-generation hybrids are viable and fertile, but when they mate with one another or with either parent species, offspring of the next generation are feeble and sterile.)

Question 31

23. describe and explain sympatric speciation.

Answer 31

In sympatric speciation, speciation occurs in populations that live in the same geographical area. Sympatric speciation can occur if gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection. Sympatric speciation requires the emergence of a reproductive barrier that isolates a subset of a population without geographical separation from the parent population. A common mechanism, especially in plants, is allopolyploid: hybridisation between closely related species coupled with errors during cell division that lead to fertile polyploid individuals. Sympatric speciation can also result when a subset of a population becomes reproductively isolated because pf a switch to a habitat, food source, or other resource not used by the parent population. In animals, speciation can also result from sexual selection in a polymorphic (?having any varieties) population.

Question 32

24. describe and explain coevolution and adaptive radiation.

Answer 32

Coevolution is the complementary evolution of associated organisms, which interact with an obvious ecological relationship (e.g., the predator and its prey, the flower, and the pollinator). Adaptive radiation refers to the adaptation (via genetic mutation) of an organism which enables it to successfully spread, or radiate, into other environments. Adaptive radiation leads to speciation and is only used to describe living organisms. Adaptive radiation can be opportunistic or forced through changes to natural habitats (is found in all animals today, as no species resembles its ancestor).

Question 33

25. explain how a new species evolves (including annidation).

Answer 33

Adaptation to different ecological niches or specialization for an ecological niche (= Total requirements made by the species on its environment; the demands are determined by the impact of environmental factors and by the usage of vital resources) is called annidation -> there is no competition between the species. An example are Darwin’s finches. Each of the 13 finch species occupies its own ecological niche and is specialized for it, e.g., cactus finches were adapted to feed on nectar and flesh of cacti; the warbler finch being adapted to use their pointed beaks to pick insects off the bark of trees. IF two species are sympatric (live in the same geographical area) and therefore compete for similar food resources, there is further specialization (contrast production) to avoid competition.

Question 34

26. name/identify/distinguish between homologous and analogous structures.

Answer 34

- Homologous structures are such structures that do not show exact similarity in their appearance and function but are linked with their common ancestor. - Analogous structures are such structures that are similar in their function and appearance but do not have any links between their ancestors. 1. name the criteria of homology and explain the role of homology in identifying evolutionary relationships 1. Criterion of position: Structures are homologous if they are always found in the same place within the complex arrangement of other structures. 2. Criterion of specific quality: Complex structures are homologous (independent from their position inside the organism) if they correspond in many specific details. 3. Criterion of continuity: Structurally different organs are homologous if they can be connected by an intermediate form and gradual transitions can be recognized.

Question 35

27. explain how analogous structures (analogies) may arise as a result of convergence.

Answer 35

A convergence (resulting from convergent evolution) is a process that occurs when two systematically separate species become similar owing to independent evolution rather than to having a common ancestor. The Existence of analogous structures in different species suggests the occurrence of convergent evolution. If unknown species all share the same habitat, they will adapt to that environment. If you compare the general body form of ichthyosaurs, penguins and dolphins, all species that took up the aquatic lifestyle, one can see that their body has adapted be more aquatic. Note that the flipper shape in mammals, birds, and reptiles is a result of convergence, but its origin from the pentadactyl limb is an example of homology

Question 36

28. describe how the change of a specific environmental factor could have resulted in the extinction or decline of a population and describe the role of extinction in evolution

Answer 36

A general deterioration of the environment caused by climate change or some major cosmic, geological, or biological event, is deemed the principal cause of extinctions. This environmental factor changes, causing the mass eradication or extinction of an effected species, who’s natural environment has changed so much that it can no longer survive. When a species disappears, biologists say that the species has become extinct. By making room for new species, extinction helps drive the evolution of life. Over long periods of time, the number of species becoming extinct can remain fairly constant, meaning that an average number of species go extinct each year, century, or millennium. • describe examples of evolution (including speciation). Include important features of the species divergence/separation. • Speciation is the evolutionary process by which new species arise (from a parent species). It occurs when two populations diverge genetically so much from each other that the individuals of the different populations can no longer interbreed and produce viable fertile offspring. • An example of speciation is the Galápagos finch. Different species of these birds live on different islands in the Galápagos archipelago, located in the Pacific Ocean off South America. The finches are isolated from one another by the ocean. • Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population Anagenesis does not always lead to the formation of a new species from an ancestral species.[2] When speciation does occur as different lineages branch off and cease to interbreed, a core group may continue to be defined as the original species. The evolution of this group, without extinction or species selection, is anagenesis.[3] • Extinction (see above)

Question 37

29. name and describe the causes of genetic variation.

Answer 37

Caused by mutation (which can create entirely new alleles in a population Random fertilization Recombination between homologous chromosomes during meiosis (which reshuffles alleles within and organism’s offspring

Question 38

30. compare sexual and asexual reproduction.

Answer 38

Asexual reproduction involves one parent and produces offspring that are genetically identical to each other and to the parent. Examples of asexual reproduction are observed in bacteria, most fungi, and some vertebrates like lizards. Sexual reproduction involves two parents and produces offspring that are genetically unique. Examples include higher organisms like humans and other mammals, and plants.

Question 39

Describe examples of evolution (including speciation). Include important features of the species divergence / separation

Answer 39

An example of speciation is the Galápagos finch. Different species of these birds live on different islands in the Galápagos archipelago, located in the Pacific Ocean off South America. The finches are isolated from one another by the ocean. Peppered Moth This light-colored moth became darker after the Industrial Revolution due to the pollution of the time. This mutation allowed dark peppered moths to blend into their sooty surroundings and avoid being eaten by predators. Soon most peppered moths were black instead of light — but notably, the lighter color returned to the population when pollution declined.