Genetics and Evolution - Biology

Before any truly accurate scientific work on evolution and inheritance could be done, the academic community had to accept the notion that the Earth and its species change over time. If species were fixed, then genetic variation, natural selection, and evolution could not be plausible. Once the scientific community acknowledged the changes in organisms, they were able to proceed into studies to determine why and how such changes occur.

Structures that are similar as a result of convergent evolution are referred to as analogous structures, such as the wings of beetles and birds. These animals do not share a common ancestor, and developed the trait for wings independent of one another. Homologous structures arise when two organisms share a trait due to linkage with a common ancestor. For example, legs of a dog and the legs of a cat are considered homologous.

Phylogeny refers to the evolutionary history of a lineage, and can be used to identify common ancestors. Taxonomy is the naming and classification of organisms. Binomial nomenclature is the scientific name for an organism containing its genus and species.

Darwin's finches were distinct from one another due to the size and shape of their beaks. Darwin noted that these distinct beaks allowed the different birds to eat specific food groups. The varying food groups allowed the animals to coexist in the same habitat, without resorting to competing for natural food resources. Each species had evolved to occupy a unique ecological niche in order to survive with minimal competition for resources.

Evolution is a theory that accounts for the changing and transformation of organisms throughout history. For evolution to take place, mutations must occur and change the genetic identity of a population. Essentially, evolution is evidenced by changes in genetic diversity and allele frequency. Each of the answer choices contributes towards the theory of evolution.

Natural selection was coined by Darwin, whose work helped with the theory, and describes the tendency for traits that aid in survival to become more prevalent in a population. Vestigial structures are organs in modern organisms that serve no purpose in increasing biological fitness, but may have been useful to ancestral species in history. Common ancestor organisms are different species that share genetic information with modern species, suggesting that genetic changes in the historic species may have produced the modern species. The fossil record provides genetic material and physical evidence of historic species to use for comparison with modern organisms.

When parts of an animal serve different functions but have similar placement and bone structure (such as a wolf forearm and a whale flipper) and are derived from a common ancestor, these two structures are homologous. Convergent evolution is a process during which two non-related organisms develop analogous structures that serve the same function but have different structures. The bottleneck effect refers to the decrease in genetic diversity that occurs when a population goes through sudden decline and then expands again. Mendel's laws of inheritance refer to the rules by which different traits, or alleles, are passed on from one generation to the next as discrete units of inheritance called genes.

The correct answer is that mitochondrial DNA is found in the mitochondria, where it takes the form of a plasmid, or ring-shaped structure characteristic of bacterial DNA. (This provides evidence in favor of the endosymbiotic theory.) Furthermore, in humans and in many other organisms, mitochondrial DNA is passed down solely through the maternal line. Note that the answer choice "It is found in a plasmid in the nucleus" is inherently non-sensical; plasmids are characteristic of prokaryotes, which do not have nuclei, as they do not have membrane-bound organelles.

All of these are true. There is lots of evidence supporting the endosymbiotic theory. The mitochondrial genes, in addition to the genes in the nucleus, are also needed to make a functional mitochondrion. These genes are contained in a singular circular chromosome, the same way bacterial genes are organized. Also, when translating their mRNA, they use the same ribosome structure as prokaryotes (70s). The mitochondria are not replicated the same way as other organelles or structures; they undergo binary fission.

Homologies are physical similarities resulting form common ancestry. This is the reason that related species share similar features. Therefore, homologous structures are anatomical similarities in organisms due to a shared ancestry. On the other hand, analogous structures are the result of convergent evolution. Convergent evolution is defined as the evolution of similar anatomical features in independent evolutionary lineages. In response to a changing environment, natural selection favored animals with similar traits or features that evolved independently as a result of adaptation to environmental alterations.

Analogous structures are anatomical structures that have similar functions, but arose independently. Due to environmental stresses and natural selection, organisms of different species evolved and adapted independently, resulting in the existence of body parts with similar functions. This refers to convergent evolution. An example of analogous structures are the wings of several different animals. A moth, hummingbird, and a bat are only extremely distantly evolutionarily related, yet they all have wings of some sort, which serve the common purpose of transportation through air. Homologous structures are body parts that are anatomically similar and may share similar anatomical forms, but are not the result of convergent evolution, rather they are the result of divergent evolution. These commonalities within organisms show descent from a common ancestor. An example of homologous structures are the "arms" of three different mammals, a human, a bat, and a whale. Each "arm" has very similar anatomical organization of bones, but is used for very different functions.

A vestigial trait is an attribute that has lost its function but has been retained through evolution. Examples include the formation of goose bumps in humans and pelvic remnants in boas and pythons. A change in the DNA sequence (genome) of a cell is a mutation. A trait that makes an organism better suited for a habitat is an adaption. Structures that arise in organisms that share a common ancestor, but perform different structures are called homologous structures. An example of a homologous structure is the "arm" of a mammal. Mammals have very similar bone and muscle organization in their arms (whales, humans, bats), but the function of each is much different (swimming, grabbing, flying).

It is believed that all organisms are descended from a common ancestor. Evidence of this includes morphological similarities, vestigial characteristics, and observations made within the fossil record. Recently, phylogenetic trees and cladograms are made using DNA sequence analysis to determine the similarity in the genomes of organisms.

Homologous structures show the existence of a shared ancestry through the observation of structural similarities between different species; however, while a human's hand and a cat's paw are structurally similar, they have very different functions.

By definition, vestigial structures are structures that are thought to have had a biological function a long time ago but have since lost that function due to evolutionary changes. The human appendix is considered to be an example of a vestigial structure.

When a mutation in a gene prevents it from being read, it may be advantageous if the compound produced by the encoded enzyme can be readily obtained from outside sources, saving energy needed to produce the compound on one's own.

A well-known example of this is the GLO gene for vitamin C production. In fruit-eating animals like bats, guinea pigs, and humans, the gene is still present but has a broken promoter, rendering it nonfunctional.

An atavistic trait is a rare appearance of an ancestral structure in an evolved organism. Since dolphins evolved from four-legged mammals, a dolphin born with a pair of hind flippers shows is an atavism, an evolutionary throwback.

Ear wiggling is a an example of a vestigial trait. A rhino's horn in relation to a ram's horn represents an analogous vs. homologous structure. Facial recognition in crows is believed to be a product of coevolution.

The biological fitness of an organism is dependent on its ability to survive and reproduce in a given environment. If different traits or alleles increase the fitness of an organism, those alleles will consequently increase in the gene pool, and that trait will increase in the population. This is how natural selection affects a population.

There is inherent trade-off in biological fitness. A trait that increases ability to survive, but makes an individual sterile, decreases fitness because the organism cannot produce offspring to carry on the trait. Similarly, if a trait increases the ability to reproduce, but makes it harder to the organism to survive, it may die before being able to produce offspring. Both survival and reproduction are essential to defining the fitness of an organism.

Biological fitness in the evolutionary sense is only related to fitness in terms to reproduction. Because the primary goal of all organisms is to reproduce, or to pass their DNA onto offspring, fitness is defined as the ability to reproduce and create viable offspring.

"Favorable" traits, such as intelligence, size, or strength, may increase the ability of an individual to survive and reproduce, thus increasing biological fitness, but cannot be used to directly define the fitness of the individual.

All of the examples given provide an evolutionary advantage. A white rabbit in a snow covered environment has camouflage, which protects it from its predators. The same is true with the black moth living in a in a soot-covered industrial area. A cheeta that can run fastest has the greatest chance of catching prey and feeding himself/herself and his/her offspring. The same is true for a bird that can crack nuts in an area where nuts are the main source of food.

The term "fitness" in evolutionary biology means the ability of an organism to pass on its genetic material to its offspring. Biological or "Darwinian" fitness is being able to live long enough to reproduce and keep the population or species alive. Most students confuse biological fitness with physical fitness because that is the context most often associated with the word.