BIOL ch 15, 16 driving q

1. List and describe the conditions under which a theoretical population will be in Hardy-Weinberg equilibrium.

A population will be in hardy weinberg equilibrium when it follows the following assumptions: a Random mating : Individuals are mating randomly without any specific preferences. b Same allelic frequencies in male and female c absence of natural selection ; individuals of all different genotypes are equally viable and fertile. d absence of mutation: mutation will lead to change in alleles and contribute to an increase proportion of mutant alleles. e absence of migration : frequency of alleles may changes if a population migrates. f large size of population: This ensures that change in allele frequency does not change by chance

1. List and describe the mechanisms that can reproductively isolate species and prevent them from interbreeding.

A species consists of group of individuals with similar basic characters which can interbreed under natural conditions and produce fertile offsprings. The formation of new species from the existing species is called speciation. For speciation reproductive isolation is must as it helps in accumulation of variations leading to speciation. Reproductive isolation prevents gene flow between sister-populations and thus the population splits into two independent species The various mechanisms that reproductively isolate species and lead to speciation include geographical barriers, ecological barriers, genetic drift, DNA changes in the germ cells etc. Geographical barriers(glaciers, oceans or mountain ranges) restrict gene flow between sub-populations and make them reproductively isolated. The migration of individuals to new area which is reproductively isolated from original range also leads to speciation. These populations become different from each other due to genetic drift and natural selection which operate differently in these different geographical areas. Within the same geographical area the population may become reproductively isolated and lead to speciation due to ecological barriers ( having different habitats) or due to ethological barriers ( having different breeding behaviours) . A sudden, large and inheritable change in the genetic material (DNA) can also lead to speciation. It may involve change in the nucleotide pairs of a gene or change in the chromosomes of germ cells of an individual. These species may be morphologicaly similar but reproductively isolated.

3. Compare and contrast adaptive and nonadaptive mechanisms of evolution.

Adaptive evolution is driven by natural selection. It occurs when an organisms adapts to certain environmental condition. This adaptation provides survival advantage to that organism and it in turn becomes natural selected because the advantage. It can lead to speciation. Example: Giraffes whose neck were long could eat food that short neck individuals could not. This trait got naturally selected and long necked giraffe became the predominant population. Non adaptive evolution is driven by genetic drift, gene flow and mutation. Genetic drift can lead to speciation and also reduce ability of a population to survive selection pressure. This type of evolution is more affected by population migration. When some individuals separate from their parent population and migrate to inhabit a new place.

2. Propose how genetic diversity can be increased in populations and why that is beneficial.

Genetic diversity is the total genetic characterstics of a particular species population. It can be increase by events like: 1) Mutations 2) out breeding i.e. random mating 3) random fertilization of gametes 4) recombination between homologous chromosomes during meiosis (gamete formation) Genetic diversity is beneficial as it allows species to survive sudden changes in environmental conditions or certain natural events. Example If a species encounters a deadly disease which can wipe off its entire population, then a highly genetic diverse species has more chances of containing genes to resist the disease and carry forward the population. Also genetic diversity allows the suppression of genetic disease. In poorly diverse small population, there are high chances of inbreeding. Inbreeding can lead to unmasking of genetic defects. Example Huntington disease in afrikaner population. Due to inbreeding, huntington disease is higly prevalent in the population.

1. Compare and contrast the mechanisms of genetic drift.

Genetic drift is the change in allelic or genotype frequency of a population because of reduced population size. Different mechanisms of genetic drift are founder effect and genetic bottleneck. Both types lead to a decrease in genetic variation. Founder effect is seen when a small group of individuals becomes isolated/ separated from their larger populations. This small group is known as founder population. The population which it establishes has a different gene pool from the population it was originated. This variation from the parent population arises because of sampling difference. If a larger proportion of individuals were separated, then it was more likely to resemble the parent population. Example : The frequency of huntington disease gene is very high in afrikaner population in south africa. This is because the founder population of afrikaner happened to carry that gene in unusually high frequency. On the other hand, Genetic bottleneck is seen, when due to certain evolutionary events a populations gets reduced in size.Some natural disasters can lead to killing of large number of individuals of a population In the resultant population. some genes may have more occurance then others and some other may be totally deleted off the population. This leads to change in genotype frequency. Genetic bottleneck is a random/ chance event.

2. Explain speciation and how it might benefit or harm a population.

Speciation leads to the formation of evolved species which are better adapted to the environment but sometimes speciation can lead to loss of gene pool.

1. Illustrate and discuss the concept of intermediate, or transitional, fossils, using Tiktaalik as an example. Explain why transitional or intermediate fossils like that of Tiktaalik are so important for the study of evolution.

Transition fossil: Fossils of an organism that shows an intermediate state between the ancestral form And that old the descendant form of a species is referred as the transitional special. In easy words: Older formofthespecies ? middle form ? descendant form lleform -> descenod The middle form or the fossil has both the features of the ancestor and the descendant. One example of such case is the Tiktaalik which is first discovered in Canada in 2004. This 'fish' was the first to explore the terrestrial living. They were an intermediate of a fish and an amphibians. It has features like that of the fish- gills and fins which is the characteristics of a fish. But it also had a flat head Like that of a crocodile and they also had ribs. What made it more different from the fish is how it's neck was placed. Fishes don't have a functional neck but a Tiktaalik head was not connected to a shoulder which made the neck functional which is not the same for the fish. Fishes do not have a functional neck. They lived in the water, they could have pribapro survived in the shoreline as it's frint fins made it difficult for Tiktaalik to walk in the land. So they lived mostly in the shallows. These help in understanding the divergence in the evolution. Also, this Fossils shows the evolutionary relationship between organisms. And it helps in a way to prove that Darwinian theory is right.