Evolution & Genetic Drift
Evolution and Genetic Drift
The variety of human attributes evident in society comes as a result of the variety of alleles that direct the expression of human genotypes. This expression results in very different phenotypic traits that form the basis of human individuality. Based upon these traits, a person may be more or less likely to adapt well to their environment. When viewed over a long enough time period, the frequency of allele distribution results in more or less advantageous phenotypes. Those phenotypes that are less adaptive to the surroundings make it harder for that individual to survive. This is the basis of natural selection, where desirable traits are selected for based upon the advantages that the phenotype confers. This is also the reason for changing allele frequencies, as those gene variants that are less helpful to the organism become (over time) less common in the population. "These ever-present and interacting forces of... genetic drift and...natural selection work to differing degrees to shape populations." (Lewis 242).
Although there are only two alleles for a particular gene in any given individual (one on each matching chromosome), there are usually many possible alleles for a trait within a population. When allele frequencies aren't changing, the population is said to be in a state of Hardy-Weinberg equilibrium. This is often not the case, however, as various positive characteristics allow for that allele frequency to grow, and numbers of deleterious alleles to decline (and sometimes vice versa). There are many reasons for changing allele frequencies within a population. These include nonrandom mating (where one chooses a spouse based upon some nonrandom process), migration and genetic drift, among others.
Underpinning evolution and natural selection is the concept of gene flow. When various alleles move through the population based upon migration patterns and mating, the allele...
Biology Unit A punnett square is a two by two square which is used to predict the possible phenotypes of offspring, and its ratio. (Krough) b) The male and female gametes contain only one set of alleles. (Krough) c) The genes of the parents go on the outside of the boxes. (Krough) d) The possible gene outcome from the parental genes goes inside the boxes. (Krough) e) The punnett square always contains only 4 boxes
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