Gene Flow: The movement of alleles into and out of a gene pool. Migration of an organism into different areas can cause the allelic frequencies of that population to increase. Most populations are not isolated, which is contrary to the Hardy-Weinberg Theorem. (H-W assumes the population isolated from others) 3. Mutations: These changes in the genome of an organism are an important source of natural selection. (H-W assumes no net mutation) 4. Nonrandom mating: Inbreeding is a popular form of nonrandom mating. Individuals will mate more frequently with close individuals than more distant ones. Assertive mating, is another form of non-random mating.
Here the individuals will mate with partners that closely resemble themselves in certain characteristics. Assertive mating decreases heterozygous *distorted mating increases heterozygous *allele frequency does not change (H-W assumes random mating) 5. Natural Selection: Populations vary in the types of individuals and their reproductive success. Those individuals who leave more offspring behind than others, pass on more of their alleles and have a better success rate in dominating the population. (H-W assumes no natural selection) Genetic Drift occurs in 1)Bottlenecks-large population goes through a catastrophe and a few thousand survive egg.
Modern Humans 2)Founder Events-move out of home population origin into a new environment -*in small populations, allele frequencies happen by chance It decreases genetic variation and heterozygous Founder Events and Disease -in Newfoundland, RAVE occurs when muscular walls of human heart thicken; the spread of this disease comes from an ancestor that carried the gene for this disease Gene Flow occurs in faster organisms in behavior and movement (egg. A hummingbird vs.. Turtle) (2. H-W assumes population is isolated) -gain and loss of alleles- make 2 pop. Dissimilar Directional Selection-changes the average value of a trait egg. In giraffe necks, there as a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks. Egg.
Artificial selection in agriculture is usually Directional Selection such as farmers select turkey with larger breasts b/c it’s more valuable Stabilizing Selection- reduces the amount of variation in a trait egg. Short height and tall height of sunflowers is balanced with an average height in order to gain the right amount of sunlight Disruptive Selection- increases the amount of variation in a trait egg. If population of rabbits occurred in an environment that had areas of black rocks as well as areas of white rocks, the rabbits with black fur would be able to hide from predators amongst the black rocks, and the rabbits with white fur likewise amongst the white rocks.
The rabbits with grey fur, however, would stand out in all areas of the habitat, and would thereby suffer greater predation Red blood cell shape -Homozygous Blood Type in dominant and recessive dies of malaria -Heterozygous Blood type lives to reproduce Heterozygous Advantage -sickle cell anemia-recessive allele with deleterious impacts Sexual recombination goes not change allele frequencies in a population Neutral Selection-Not all genetic variation has implications for survival or reproductive success – some are selectively neutral -DNA variation may be neutral now… But be (disc)advantageous later Mutation is the only mechanism that makes new alleles (1 . H-W assumes no net mutation) Non- random mating ARREAR occurs in Northern Spain and is a Parkinson-related disease; in Spain, the Basque have imposed cultural isolation inbreeding causing 4. 0% Inbreeding in small isolated populations – mating between relatives more likely – deleterious effects due to increased homozygous Natural selection never expects environmental change Why would there be genetic variation between populations of the same species? Environmental differences and Historical legacy (inch. Genetic drift) Frequency- dependent selection-selective advantage of a trait is dependent on its frequency Spatial and temporal variability- seasonality – different traits are (disc)advantageous at different times; patchy environments within a population’s range Agent Definition Detect on Genetic Variation Mutation Change in DNA increases Gene Flow Change in allele frequencies as individuals Join a population and reproduce
Introduces new alleles to another population; increases and decreases Genetic Drift Random allele changes caused by chance events Reduces Natural Selection Different survival rates due to different genotypes One alleles dominates another or variation is preserved Non-random mating Choice of mates based on common phenotype and genotype Does not directly affect frequencies but imbalances genetic equilibrium Learning Objective Answers Describe and explain unconventionally processes. Microinstruction explains how individual traits in a population change over time The H- W principle says in order for a population to change, there are 5 assumptions in which they occur This is natural selection, migration, mating, mutations or genetic drift Natural Selection Of course, natural selection is the main mechanism for microinstruction. Alleles that produce favorable adaptations are more likely to be passed down to future generations because they allow those individuals to live long enough to reproduce. As a result, unfavorable adaptations are eventually bred out of the population and those alleles are removed from the gene pool.
Over time, changes in allele frequency come more apparent when compared to previous generations. Gene Flow Migration is the movement of individuals into or out of a population. Just like the migration of birds from the north to the south in the winter, organisms will sometimes change their locations and therefore change the gene pool of that population. If a new individual moves into a population, that is called immigration. If an individual moves out of a population, that is called emigration. Immigration causes different alleles to be introduced into the population and those are now available to be passed down via breeding with other members of the population.
Emigration results in the loss of alleles from a population, which in turn would decrease the available genes in the gene pool. Mating Many species are not selective when it comes to mating. Asexual reproduction essentially clones the parent by copying its alleles without any sort of mating between individuals. Some species that use sexual reproduction will choose any available individual that is available as a partner with no regard for which characteristics they show. This keeps the alleles that are being passed down from generation to generation random. However, many animal species are selective when ending a mate. These individuals look for particular traits in a mate that will translate to an advantage for their offspring.
Since this mating is no longer random, many undesirable alleles are bred out tot the population over several generations. T makes the gene pool shrink and fewer traits available for the next generation, causing microinstruction. Mutations Mutations change alleles by changing the actual DNA of the organism. There are several types of mutations that can occur and have varying degrees of change that accompany them. Alleles may not necessarily change if the change in DNA is small, eke a point mutation, but could be lethal to organisms if it has a profound change, like a frame shift mutation. This change in DNA, if it occurs in the gametes can be passed down to the next generation. This either creates new alleles or removes existing traits from the population.
However, cells are equipped with a system of checkpoints to make sure mutations do not occur and are corrected if they do. Mutations within populations that actually change the gene pool are rare. Genetic Drift The smaller a population, the more likely it is to see significant microinstruction related differences over generations. One of these changes that often happens randomly is called genetic drift. These changes are caused by the environment and other factors in every day life. The survival and reproduction of individuals could be affected and in turn change the frequency of some alleles seen in future generations of the population. Genetic drift is not the same as mutations.
While some environmental factors can mutate the DNA, genetic drift has more to do with behaviors, such as breeding times or geographic obstacles for smaller organisms. Identify, given a scenario, which form(s) of natural selection is/are at work. Answer: Describe how an organism’s phenotype represents a compromise or “trade-off’ between the adaptive value of multiple traits. Population: group of organisms of one species Microinstruction: small-scale changes, I. E. Within the kind, occurring over a short period of time that results in the formation of new species. Gene pool-all alleles of all the genes in a certain population Allele Frequency- frequency of a particular allele in the population. Mom alleles will be more common than others, thus more individuals will express this trait Genetic equilibrium: a gene pool is not changing n frequency because the evolutionary forces acting upon the allele are equal Loci/ locus chromosomal position of a gene as determined by its linear order relative to the e otherness on that chromosome Fixation-when the frequency of a gene is stable in a population. When a new type of gene is introduced into the genome it can be beneficial enough that its possessors are more reproductively successful, thus driving the gene to fixation. Explain how a single point-source mutation in DNA has a wide range of possible evolutionary consequences. Answer: No change occurs in phenotype. Small change occurs in phenotype. Big change occurs in phenotype. Sickle cell anemia is a genetic disease with severe symptoms, including pain and anemia.
The disease is caused by a mutated version of the gene that helps make hemoglobin -? a protein that carries oxygen in red blood cells. People with two copies of the sickle cell gene have the disease. People who carry only one copy of the sickle cell gene do not have the disease, but may pass the gene on to their children. The mutations that cause sickle cell anemia have been extensively studied and demonstrate how the effects of mutations can be traced from the DNA level up to the level of the whole organism. Consider someone carrying only one copy of the gene. She does not nave the disease, but the gene that seen carries still a detects her, her cells, and her proteins: 1. There are effects at the DNA level 2.
There are effects at the protein level Normal hemoglobin (left) and hemoglobin in sickles red blood cells (right) look different; the mutation in the DNA slightly changes the shape of the hemoglobin molecule, allowing it to clump together. 3. There are effects at the cellular level When red blood cells carrying mutant hemoglobin are deprived of oxygen, they become “sickle-shaped” instead of the usual round shape (see picture). This shape an sometimes interrupt blood flow. 4. There are negative effects at the whole organism level Under conditions such as high elevation and intense exercise, a carrier of the sickle cell allele may occasionally show symptoms such as pain and fatigue. 5.
There are positive effects at the whole organism level Carriers of the sickle cell allele are resistant to malaria, because the parasites that cause this disease are killed inside sickle-shaped blood cells. This is a chain of causation. What happens at the DNA level propagates up to the level of the complete organism. This example illustrates how a single mutation can have a large effect, in his case, both a positive and a negative one. But in many cases, evolutionary change is based on the accumulation of many mutations, each having a small effect. Whether the mutations are large or small, however, the same chain of causation applies: changes at the DNA level propagate up to the phenotype.
Describe how organism mobility and gamete mobility influence rates of gene flow between populations. Answer: occurs in faster organisms in behavior and movement. Many organisms are divided into separate populations that have restricted contact with each other, possibly leading to reproductive isolation. Gene flow between populations limits this genetic divergence, serving to inhibit the development of separate species out of the two separated populations. Essential mechanism of gene flow is movement of individuals (or their gametes) between populations. For example, gene flow can occur in plant species when pollen is carried by bees or blown by the wind from one population of flowering plants to another.
Because each individual can have different alleles, when only a subset of individuals reproduce, allele frequencies change from generation to generation, and some alleles may be lost. A change in allele frequency due to random chance is known as genetic drift, whereas a change due to differences in reproductive fitness is known as natural selection. Gene flow between isolated populations slows down their genetic drift from each other and reduces the power of natural selection to promote divergence between them. Describe various mechanisms by which natural selection does not lead to the elimination of genetic variation. Answer: mutation, gene flow, disruptive selection, Calculate frequencies of alleles or genotypes given information on the number of individuals with specific genotypes.