Biology: please give me an idea on my paper topic !!!?

Question

an invertebrate structure or group of structure in a single species or group of species, the funchtion of the structure(s) and the importance of teh structure to the evolution of the species and survivalof the individual.......>< please help me choosing a topic. Thanks a lot

Answer 1

better choose second one since u can explain more. try adding this:
Basic processes
Evolution consists of two basic types of processes: those that introduce new genetic variation into a populus, and those that affect the frequencies of existing genes.[10] Random copying errors in genetic material (mutations), migration between populations (gene flow), and the reshuffling of genes during sexual reproduction (genetic recombination) create variation in organisms. In some organisms, like bacteria and plants, variation is also produced through horizontal gene transfer (the transfer of genetic material between organisms that are not directly related) and the mixing of genetic material by hybridization (interbreeding between species).

Genetic drift and natural selection act on this variation by increasing or decreasing the frequency of traits: genetic drift does so randomly, while natural selection does so based on whether a trait is beneficial, or conducive to reproduction.

The variation in a population's apparent traits, or phenotypes, is primarily the result of the specific genetic makeup, or genotypes, encoded on DNA molecules called chromosomes. A specific location on a chromosome is known as a locus; a variant of a DNA sequence at a given locus is an allele. The modern evolutionary synthesis defines evolution as the change in the relative frequencies of alleles in a population. The variation between different DNA codings (alleles) at various loci is thus considered responsible for evolutionary change.

Genetic variation is often the result of a new mutation in a single individual; in subsequent generations, the frequency of that variant may fluctuate in the population, becoming more or less prevalent relative to other alleles at the site. All evolutionary forces act by driving this change in allele frequency in one direction or another. Variation disappears when an allele reaches the point of fixation—when it either reaches a frequency of zero and disappears from the population, or reaches a frequency of one and replaces the ancestral allele entirely.

Most sites in the complete DNA sequence, or genome, of a species are identical in all individuals in the population. Consequently, relatively small genotypic changes can lead to dramatic phenotypic ones. Sites with more than one allele are called polymorphic, or segregating, sites. Polymorphism leads to distinct groups of traits arising within the same species, such as different hair colors or sexes. Interactions between a genotype and the environment may also affect the phenotype, as reflected in developmental and phenotypic plasticity.

Genetic variation arises due to random mutations that occur at a certain rate in the genomes of all organisms. Mutations are permanent, transmissible changes to the genetic material (usually DNA or RNA) of a cell, and can be caused by: "copying errors" in the genetic material during cell division; by exposure to radiation, chemicals, or viruses. In multicellular organisms, mutations can be subdivided into germline mutations that occur in the gametes and thus can be passed on to progeny, and somatic mutations that can lead to the malfunction or death of a cell and can cause cancer.

Mutations that are not affected by natural selection are called neutral mutations. Their frequency in the population is governed by mutation rate, genetic drift and selective pressure on linked alleles. It is understood that most of a species' genome, in the absence of selection, undergoes a steady accumulation of neutral mutations.

Individual genes can be affected by point mutations, also known as SNPs, in which a single base pair is altered. The substitution of a single base pair may or may not affect the function of the gene, while deletions and insertions of base pairs usually results in a non-functional gene.[14]

Mobile elements, transposons, make up a major fraction of the genomes of plants and animals and appear to have played a significant role in the evolution of genomes. These mobile insertional elements can jump within a genome and alter existing genes and gene networks to produce evolutionary change and diversity.[15]

On the other hand, gene duplications, which may occur via a number of mechanisms, are believed to be one major source of raw material for evolving new genes as tens to hundreds of genes are duplicated in animal genomes every million years.[16] Most genes belong to larger "families" of genes derived from a common ancestral gene (two genes from a species that are in the same family are dubbed "paralogs"). Another mechanism causing gene duplication is intergenic recombination, particularly "exon shuffling", i.e., an aberrant recombination that joins the "upstream" part of one gene with the "downstream" part of another.[17] Genome duplications and chromosome duplications also appear to have served a significant role in evolution. Genome duplication has been the driving force in the Teleostei genome evolution, where up to four genome duplications are thought to have happened, resulting in species with more than 250 chromosomes.

Large chromosomal rearrangements do not necessarily change gene function, but do generally result in reproductive isolation, and, by definition, speciation; in sexual organisms, species are usually defined by the ability to interbreed). An example of this mechanism is the fusion of two chromosomes in the Homo genus that produced human chromosome 2; this fusion did not occur in the chimpanzee lineage, resulting in two separate chromosomes in extant chimpanzees
Horizontal gene transfer (HGT) is any process in which an organism transfers genetic material to another organism that is not its offspring. This mechanism allows for the transfer of genetic material between unrelated organisms and is a form of gene flow.

Many mechanisms for horizontal gene transfer have been observed, such as antigenic shift, reassortment, and hybridization. Viruses can transfer genes between species via transduction. Bacteria can incorporate genes from other dead bacteria or plasmids via transformation, exchange genes with living bacteria via conjugation, and have plasmids "set up residence separate from the host's genome".[18] Hybridization is highly significant in plant speciation,[19] and one out of ten species of birds are known to hybridize.[20] There are also examples of hybridization in mammals and insects;[21] however, this most often results in sterile offspring.

Horizontal gene transfer has been shown to result in the spread of antibiotic resistance across bacterial populations.[22] Furthermore, findings indicate that HGT has been a major mechanism for prokaryotic and eukaryotic evolution.[23][24]

Horizontal gene transfer complicates the inference of the phylogeny of life, as the original metaphor of a tree of life no longer fits. Rather, since genetic information is passed to other organisms and other species in addition to being passed from parent to offspring, "biologists [should] use the metaphor of a mosaic to describe the different histories combined in individual genomes and use [the] metaphor of a net to visualize the rich exchange and cooperative effects of HGT among microbes".[25]

Natural selection comes from differences in survival and reproduction. Differential mortality is the survival rate of individuals to their reproductive age. Differential fertility is the total genetic contribution to the next generation. Note that, whereas mutations and genetic drift are random, natural selection is not, as it preferentially selects for different mutations based on differential fitnesses. For example, rolling dice is random, but always picking the higher number on two rolled dice is not random. The central role of natural selection in evolutionary theory has given rise to a strong connection between that field and the study of ecology.

Natural selection can be subdivided into two categories: ecological selection occurs when organisms that survive and reproduce increase the frequency of their genes in the gene pool over those that do not survive; and sexual selection occurs when organisms which are more attractive to the opposite sex because of their features reproduce more and thus increase the frequency of those features in the gene pool.

Natural selection operates on mutations in a number of different ways. Arguably the most common form of selection is stabilizing selection, which decreases the frequency of harmful mutations; "living fossils" may be a result of this. Other forms of natural selection include directional selection, which increases the frequency of a beneficial mutation, and artificial selection, the purposeful breeding of a species.

Through the process of natural selection, organisms become better adapted to their environments. Adaptation is any evolutionary process that increases the fitness of the individual, or sometimes the trait that confers increased fitness, e.g., a stronger prehensile tail or greater visual acuity. Note that adaptation is context-sensitive; a trait that increases fitness in one environment may decrease it in another.

Most biologists believe that adaptation occurs through the accumulation of many mutations of small effect. However, macromutation is an alternative process for adaptation that involves a single, very large-scale mutation.


In asexual organisms, variants in genes on the same chromosome will always be inherited together—they are linked, by virtue of being on the same DNA molecule. However, sexual organisms, in the production of gametes, shuffle linked alleles on homologous chromosomes inherited from the parents via meiotic recombination. This shuffling allows independent assortment of alleles (mutations) in genes to be propagated in the population independently. This allows bad mutations to be purged and beneficial mutations to be retained more efficiently than in asexual populations.

However, the meitoic recombination rate is not very high - on the order of one crossover (recombination event between homologous chromosomes) per chromosome arm per generation. Therefore, linked alleles are not perfectly shuffled away from each other, but tend to be inherited together. This tendency may be measured by comparing the co-occurrence of two alleles, usually quantified as linkage disequilibrium (LD). A set of alleles that are often co-propagated is called a haplotype. Strong haplotype blocks can be a product of strong positive selection.

Recombination is mildly mutagenic, which is one of the proposed reasons why it occurs with limited frequency. Recombination also breaks up gene combinations that have been successful in previous generations, and hence should be opposed by selection. However, recombination could be favoured by negative frequency-dependent selection (this is when rare variants increase in frequency) because it leads to more individuals with new and rare gene combinations being produced.

When alleles cannot be separated by recombination (for example in mammalian Y chromosomes), there is an observable reduction in effective population size, known as the Hill-Robertson effect, and the successive establishment of bad mutations, known as Muller's ratchet.

Gene flow, also called migration, is the exchange of genetic variation between populations, when geography and culture are not obstacles. Ernst Mayr thought that gene flow is likely to be homogenising, and therefore counteracting selective adaptation. Obstacles to gene flow result in reproductive isolation, a necessary condition for speciation.

The free movement of alleles through a population may also be impeded by population structure, the size and geographical distribution of a population. For example, most real-world populations are not actually fully interbreeding; geographic proximity has a strong influence on the movement of alleles within the population. Population structure has profound effects on possible mechanisms of evolution.

The effect of genetic drift depends strongly on the size of the population: drift is important in small mating populations, where chance fluctuations from generation to generation can be large. The relative importance of natural selection and genetic drift in determining the fate of new mutations also depends on the population size and the strength of selection. Natural selection is predominant in large populations, while genetic drift is in small populations. Finally, the time for an allele to become fixed in the population by genetic drift (that is, for all individuals in the population to carry that allele) depends on population size—smaller populations require a shorter time for fixation.

An example of the effect of population structure is the founder effect, in which a population temporarily has very few individuals as a result of a migration or population bottleneck, and therefore loses much genetic variation. In this case, a single, rare allele may suddenly increase very rapidly in frequency within a specific population if it happened to be prevalent in a small number of "founder" individuals. The frequency of the allele in the resulting population can be much higher than otherwise expected, especially for deleterious, disease-causing alleles. Since population size has a profound effect on the relative strengths of genetic drift and natural selection, changes in population size can alter the dynamics of these processes considerably.

Speciation is the process by which new biological species arise. This may take place by various mechanisms. Allopatric speciation occurs in populations that become isolated geographically, such as by habitat fragmentation or migration.[26] Sympatric speciation occurs when new species emerge in the same geographic area.[27][28] Ernst Mayr's peripatric speciation is a type of speciation that exists in between the extremes of allopatry and sympatry. Peripatric speciation is a critical underpinning of the theory of punctuated equilibrium. An example of rapid sympatric speciation can be clearly observed in the triangle of U, where new species of Brassica sp. have been made by the fusing of separate genomes from related plants.

One common misconception about evolution is the idea that if humans evolved from monkeys, monkeys should no longer exist. This misunderstands speciation, which frequently involves a subset of a population cladogenetically splitting off before speciating, rather than an entire species simply turning into a new one. Cladogenesis is particularly common when two subsets of a population are isolated from each other. Additionally, biologists have never claimed that humans evolved from monkeys—only that humans and monkeys share a common ancestor, as do all organisms.[29]

Extinction is the disappearance of species (i.e., gene pools). The moment of extinction is generally defined as occurring at the death of the last individual of that species. Extinction is not an unusual event on a geological time scale—species regularly appear through speciation, and disappear through extinction. The Permian-Triassic extinction event was the Earth's most severe extinction event, rendering extinct 90% of all marine species and 70% of all terrestrial vertebrate species. In the Cretaceous-Tertiary extinction event, many forms of life perished (including approximately 50% of all genera), the most commonly mentioned among them being the non-avian dinosaurs. The Holocene extinction event is a current mass extinction, involving the rapid extinction of tens or hundreds of thousands of species each year. Scientists consider human activities to be the primary cause of the ongoing extinction event, as well as the related influence of climate change.[30]

[edit] Cooperation
Generally mathematical models incorporating mutation and natural selection have been used to model adaptation and evolution. Recent trends now incorporate "game theory" as more applicable to generating reliable models.[31] This work and others studies have focused attention on cooperation as a fundamental property needed for evolution to construct new levels of organization. Selfish replicators sacrificing their own reproductive potential to cooperate seems paradoxical in a competitive world. However a number of mechanisms have demonstrated the capacity to generate cooperation, and even altruism, such as kin selection, direct reciprocity, indirect reciprocity, network reciprocity, and group selection. The ubiquity of cooperation in the natural world and studies from the last twenty years reveal cooperation as a significant principle in constructive evolution.

Answer 2

Surely, choose the function of the structure and the importance of the structure to the evolution of the species and the survival of the individual. It's more interesting as it talks about evolution and survival.